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Project Gutenberg's The Standard Electrical Dictionary, by T. O'Conor Slone

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Title: The Standard Electrical Dictionary
       A Popular Dictionary of Words and Terms Used in the Practice
              of Electrical Engineering

Author: T. O'Conor Slone

Release Date: September 5, 2008 [EBook #26535]

Language: English

Character set encoding: ISO-8859-1


Produced by Don Kostuch


[Transcriber's Notes]

Obvious spelling errors have been corrected. I have not reconciled the
variety of spellings of names and other words. Obvious factual errors,
typographical errors, discoveries made after 1892, and contemporary
(2008) theories and use of words are noted in the text within square
brackets. I have not researched and checked every assertion by the

This book was published 5 years before discovery of the electron. See
the labored and completely inaccurate explanations of aurora and
"energy, atomic". The author and his contemporaries were like fifteenth
century sailors. They had a good idea of their latitude and direction
(Ampere, Kirkoff, Maxwell, Gauss, Faraday, Edison, …), but only the
vaguest notion of their longitude (nuclear structure, electrons, ions).
Altitude (special relativity, quantum theory) was not even imagined.

Some relevant dates:
Franklin's Kite--1752
Faraday's Law of Induction--1831
Maxwell's Equations--1861
Edison's Phonograph--1877
Edison's light bulb--1879
Edison's first DC power station--1882
Michelson-Morley experiment disproving ether--1887
Hertz demonstrates radio waves--1888
Westinghouse first AC power station--1891
This book--1892
Discovery of the electron--1897
Marconi radio signals cross the English Channel--1897
First Vacuum Tube--1904
Special Relativity, photo-electric effect explained with photons--1905
General Relativity: space-time dilation and curvature--1915
Confirmation of general relativity's prediction of the deflection
  of starlight by the Sun--1919
Discovery of the proton--1920
Quantum theory--1926
Discovery of neutron--1932
First transistor--1947
Soviet satellite Luna measures solar wind--1959
Edward M. Purcell explains magnetism with special relativity--1963

Purcell's explanation of magnetism as a result of Lorentz contraction of
space along the direction of a current is a welcome relief from the
convoluted descriptions in this book.

Mathematical notation is rendered using "programming" notation.
^       Power--Exponential; A^3 means "A cubed"
*       Multiply
/       Divide
+       Add
-       Subtract
( )     Precedence--Perform before enclosing expression
2E6   Scientific Notation (2,000,000)

4.452 X 10^12 X t

is rendered as

A / ( 4.452E12 *  t  )

Where the rendering of a mathematical expression is in doubt, an image
of the original text is included.

Here are some definitions absent from the text.

Foucault currents.
  Eddy currents.

  To thicken, as by evaporation.


  Order Sapotace[ae] of trees and shrubs, including the star apple, the
  Lucuma, or natural marmalade tree, the gutta-percha tree (Isonandra),
  and the India mahwa, as well as the sapodilla, or sapota, after which
  the order is named.

Don Kostuch, MS, Electrical Engineering.
[End Transcriber's notes.]


Third Edition. Illustrated. $1.00.
It is very useful to that class of readers to whom Algebra is a
comparatively unknown quantity, and will meet its wants
admirably.--Electrical World.

Illustrated. $1. 00.
We especially recommend it to those who would like to acquire a popular
idea of the subject.--Electric Age.

Fully Illustrated. $1.00.





Copyright 1892


The purpose of this work is to present the public with a concise and
practical book of reference, which it is believed will be appreciated in
this age of electricity. The science has expanded so much that the
limits of what may be termed strictly a dictionary of the present day
would a few years ago have sufficed for an encyclopedia. It follows that
an encyclopedia of electricity would be a work of great size. Yet a
dictionary with adequate definitions, and kept within the closest limits
by the statement of synonyms, and by the consigning of all the
innumerable cross-references to a concise index will be far more than a
mere dictionary in the ordinary sense of the term.

Duplication of matter is to be avoided. This makes many definitions
appear short. Yet, by the assistance of the reader's own general
knowledge, and by referring to the very complete index, almost any
subject can be found treated in all its aspects. There are exceptions to
this statement. So much has been done in the way of mechanical detail,
so many inventions in telegraphy and other branches have sprung into
prominence only to disappear again, or to be modified out of
recognition, that to embody descriptions of many ingenious and
complicated apparatus has been absolutely impossible for want of space.

A word as to the use of the book and the system of its construction may
be given here. Each title or subject is defined once in the text. Where
a title is synonymous with one or more others the definition is only
given under one title, and the others appear at the foot of the article
as synonyms. It may be that the reader is seeking the definition of one
of these synonyms. If so a reference to the index shows him at once what
page contains the information sought for. The use of an index in a work,
necessarily of an encyclopedic form, will be appreciated by all users of
this book.


Where a title embraces several words, all orders of the words will be
cited in the index. To make the operation of finding references easy
this rule has been carried out very fully.

It is customary to regard electricity as a growing science. It is
unquestionably such, but the multiplication of terms and words is now
not nearly so rapid as it has been, and the time for the compiling of a
work of this character seems most propitious. It is hoped that the
public will indulgently appreciate the labor it has entailed on all
concerned in its production.


adj. Adjective.
v. Verb.
q.v. "Which see.'
/ A mark of division, as A/B, meaning "A divided by B."
./. The same as above.

[Transcriber's note: / will be substituted for this divide symbol.]
= A mark of equality, meaning "is equal to."
X A mark of multiplication, meaning "multiplied by."

[Transcriber's note: * will be substituted for this multiply symbol.]

Fractional exponents indicate the roots expressed by their denominators
and the powers expressed by their numerators. Thus, A^1/2 means the
"square root of A;" A^1/3 means the "cube root of A;" B^3/2 means the
"square root of the cube or third power of B."

The use of powers of ten, as 10^10, 10^11, as multipliers, will be found
explained at length in the definition "Ten, Powers of."


Abbreviation for anode, employed in text relating to
electro-therapeutics. It is sometimes written An.

In a system of plane co-ordinates (see Co-ordinates) the
distance of any point from the axis of ordinates measured parallel to
the axis of abscissas.

In the cut the abscissa of the point a is the line or distance a c.


Absolute. adj.
In quantities it may be defined as referring to fixed units of quantity,
and it is opposed to "relative," which merely refers to the relation of
several things to each other. Thus the relative resistance of one wire
may be n times that of another; its absolute resistance might be 5 ohms,
when the absolute resistance of the second wire would be 5/n ohms. A
galvanometer gives absolute readings if it is graduated to read directly
amperes or volts; if not so graduated, it may by "calibration" q. v. be
made to do practically the same thing.


Absolute Measurement.
Measurement based upon the centimeter, gram, and second. (See
Centimeter-Gram-Second System.)

Absolute Temperature.
Temperature reckoned from absolute zero (see "Zero, Absolute"). It is
obtained by adding for the centigrade scale 273, and for the Fahrenheit
scale 459, to the degree readings of the regular scale.

Absorption, Electric.
A property of the static charge. When a Leyden jar is being charged it
dilates a little and the capacity increases, so that it can take a
little more charge for a given potential difference existing between its
two coatings. This phenomenon occurs with other static condensers,
varying in degree with the dielectric. With shellac, paraffin, sulphur
and resin, for instance, the absorption is very slight; with
gutta-percha, stearine, and glass, the absorption is relatively great.
The term is due to Faraday. Iceland spar seems almost or quite destitute
of electric absorption.

A. C. C.
Symbol of or abbreviation for "anodic closure contraction" q. v.

The rate of change of velocity. If of increase of velocity it is
positive; if of decrease, it is negative. It can only be brought about
by the exercise of force and is used as the measure of or as determining
the unit of force. It is equal to velocity (L/T) imparted, divided by
time (T); its dimensions therefore are L/(T^2). The c. g. s. unit of
acceleration is one centimeter in one second.

[Transcriber's note: The unit of acceleration is "centimeters per second
per second."]

(a) A term sometimes applied to the secondary or storage battery. (See
Battery, Secondary.)
(b) See Accumulator, Electrostatic
(c) See Accumulator, Water Dropping.
(d) See Wheel, Barlow's

Accumulator, Electrostatic.
Two conducting surfaces oppositely placed, and separated by a
dielectric and arranged for the opposite charging of the two surfaces,
constitute an accumulator, sometimes termed a condenser. As this
arrangement introduces the element of a bound and of a binding charge,
the electrostatic capacity of such is greater than that of either or of
both of its component surfaces. The thinner the dielectric which
separates the conducting surfaces, and the larger the surfaces the
greater is the capacity; or the less will be the potential difference
which a given charge will establish between its two coatings. The nature
of the dielectric also determines its capacity. (See Capacity, Specific



Accumulator, Water Dropping.
This is also known as Sir William Thomson's Water-Gravity Electric
Machine. It is an apparatus for converting the potential energy of
falling water drops, due to gravity, into electric energy. Referring to
the illustration, G represents a bifurcated water pipe whose two faucets
are adjusted to permit a series of drops to fall from each. C and F are
two metallic tubes connected by a conductor; E and D are the same. Two
Leyden jars, A and B, have their inner coatings represented by strong
sulphuric acid, connected each to its own pair of cylinders, B to D and
E, and A to F and C. The outer coatings are connected to earth, as is
also the water supply. One of the jars, say A, is charged interiorily
with positive electricity. This charge, C and F, share with it, being in
electric contact therewith. Just before the drops break off from the jet
leading into C, they are inductively charged with negative electricity,
the positive going to earth. Thus a series of negatively excited drops
fall into the metal tube D, with its interior funnel or drop arrester,
charging it, the Leyden jar B, and the tube E with negative electricity.
This excitation causes the other stream of drops to work in the converse
way, raising the positive potential of F and C and A, thus causing the
left-hand drops to acquire a higher potential. This again raises the
potential of the right-hand drops, so that a constant accumulating
action is kept up. The outer coatings of the Leyden jars are connected
to earth to make it possible to raise the potential of their inner
coatings. In each case the drops are drawn by gravity into contact with
objects similarly excited in opposition to the electric repulsion. This
overcoming of the electric repulsion is the work done by gravity, and
which results in the development of electric energy.


A hydrometer or areometer used to determine the specific gravity of
acid. They are employed in running storage batteries, to determine when
the charging is completed. (See Areometer.)

Aclinic Line.
A terrestrial element; the locus on the earth's surface of no
inclination of the magnetic needle; the magnetic equator. (See Magnetic

Acoustic Telegraphy.
The system of sound-reading in telegraphy, universally used in the Morse
system. The direct stroke of the armature of the electro-magnet and its
"back stroke" disclose to the ear the long and short strokes, dots and
lines, and long and short spaces as produced by the dispatcher of the
message. In the Morse system a special magnet and armature is used to
produce the sound called the "sounder;" in other systems, e. g.,
Steinheil's and Bright's apparatus, bells are used. (See Alphabets,

A Hughes audiometer or sonometer applied to determining the quality of a
person's hearing (See Hughes' Induction Balance,--Audiometer). The
central coil by means of a tuning fork and microphone with battery
receives a rapidly varying current tending to induce currents in the
other two coils. Telephones are put in circuit with the latter and pick
up sound from them. The telephones are applied to the ears of the person
whose hearing is to be tested. By sliding the outer coils back and forth
the intensity of induction and consequent loudness of the sounds in the
telephones is varied. The position when the sounds grow so faint as to
be no longer audible, gives the degree of delicacy of the person's
hearing. By using a single telephone the same apparatus affords a means
of testing the relative capacity of the right and left ears.


Actinic Rays.
The rays of light at the violet end of the spectrum; also the invisible
rays beyond such end, or the ether waves of short periods which most
strongly induce chemical change.

The power possessed by ether waves of inducing chemical change, either
of decomposition or of combination. The violet and ultra-violet end of
the spectrum of white light, generally speaking, represent the most
highly actinic rays.

Actinometer, Electric.
Properly an apparatus for measuring the intensity of light by its action
upon the resistance of selenium. A current produced by fixed
electro-motive force passing through the selenium affects a galvanometer
more or less according to the intensity of the light. It is more
properly an electric photometer. The term has also been applied to a
combination of a thermo-electric pile and galvanometer, the light
falling on the pile affecting the motions of the galvanometer.

Action, Local.
(a) The wasteful oxydation of the zinc in a galvanic battery due to
local impurities and variations in the composition of the zinc. These
act to constitute local galvanic couples which cause the zinc to
dissolve or oxydize, without any useful result. Amalgamation of the zinc
prevents local action. Chemically pure zinc is also exempt from local
action, and can be used in an acid battery without amalgamation. (See

(b) The same term has been employed to indicate the eddy or foucault
currents in dynamo electric machines. (Sec Current, Foucault.)

The rate of doing work; the work done per second by any expenditure of
energy. The activity of a horse-power is 550 foot lbs. per second, or
746 volt-coulombs per second. The practical electric unit is the
volt-ampere, often called the watt. (Sec Energy, Electric.)

A screw coupling to engage with a different sized screw on each end; one
of the uses is to connect incandescent lamps to gas-fixtures.

A. D. C.
Abbreviation for Anodic Duration Contraction, q. v.; a term in

Adherence, Electro-magnetic.
The adherence between surfaces of iron due to elcctro-magnetic
attraction. It has been applied to the driving-wheels of an engine and
rail, whose grip is increased by such action. In one method a deep
groove was cut around the wheel which was wound with a magnetizing coil.
Thus one rim becomes a north and the other a south pole, and the rail
completing the circuit acts as the armature. Such an arrangement
prevents a wheel from sliding. Electro-magnetic adherence has also been
employed to drive friction gear wheels. In one arrangement the two
wheels are surrounded by a magnetizing coil, under whose induction each
attracts the other, developing high adherence between their peripheries.




Admiralty Rule of Heating.
The British Admiralty specifications for the permissible heating of
dynamos. It holds that at the end of a run of six hours no part of the
dynamo under trial shall show a rise of temperature greater than 11º C.
(20º F.) above the temperature of the air surrounding it. This is
thought to be a very stringent and unnecessarily high requirement.

Aerial Conductor.
An electric conductor carried from housetops, poles, or otherwise so as
to be suspended in the air, as distinguished from an underground or
submarine conductor.

The attraction of atoms and in some cases perhaps of molecules for each
other by the force of chemical attraction. When the affinity is allowed
to act or is carried out, a chemical change, as distinguished from a
physical or mechanical change, ensues. Thus if sulphur and iron are each
finely powdered and are mixed the change and mixture are mechanical. If
slightly heated the sulphur will melt, which is a physical change. If
heated to redness the iron will combine with the sulphur forming a new
substance, ferric sulphide, of new properties, and especially
characterized by unvarying and invariable ratios of sulphur to iron.
Such change is a chemical one, is due to chemical affinity, is due to a
combination of the atoms, and the product is a chemical compound.


Agir Motor.
The Anderson and Girdlestone motor. The term "agir" is made up from the
first portions of each name.

Agonic Line.
The locus of points on the earth's surface where the magnetic needle
points to the true north; an imaginary line determined by connecting
points on the earth's surface where the needle lies in the true
geographical meridian. Such a line at present, starting from the north
pole goes through the west of Hudson's Bay, leaves the east coast of
America near Philadelphia, passes along the eastern West Indies, cuts
off the eastern projection of Brazil and goes through the South Atlantic
to the south pole. Thence it passes through the west of Australia, the
Indian Ocean, Arabia, the Caspian sea, Russia and the White sea to the
North Pole. It crosses the equator at 70° W. and 55° E. approximately.
(See Magnetic Elements.)


[Transcriber's note: The file Earth_Declination_1590_1990.gif provided
by the U.S. Geological Survey ( is an animation of
the declination of the entire earth.]

Air is a dielectric whose specific inductive capacity at atmosphere
pressure is taken as 1. It is practically of exactly the same
composition in all places and hence can be taken as a standard. When dry
it has high resistance, between that of caoutchouc and dry paper.
Dampness increases its conductivity.

It is a mixture of oxygen and nitrogen, with a little carbonic acid gas
and other impurities. Its essential composition is:

Oxygen:     (by weight) 23.14     (by volume) 21   
Nitrogen:               76.86                 79

The specific inductive capacity varies for different pressures thus:

Approximate   (.001 mm., .0004 inch)   0.94 (Ayrton) 
              ( 5 mm. , .2 inches )    0.9985 (Ayrton)
                                       0.99941 (Boltzman.)

The specific gravity of air under standard conditions 15.5° C (60° F.)
and 760 mm. barometric pressure (30 inches) is taken as unity as a
standard for gases.

[Transcriber's note: Argon accounts for 0.9340%. It was discovered in
1894, two years after this book.]

(a) In the Thomson-Houston dynamo an air-blast is used to blow away the
arc-producing spark liable to form between the brushes and commutator.
It is the invention of Prof. Elihu Thomson. The air is supplied by a
positive action rotary blower connected to the main shaft, and driven
thereby. The wearing of the commutator by destructive sparking is thus

A drum H H is rotated, being mounted on the axis X of the dynamo. As it
rotates the three vanes are thrown out against the irregular shaped
periphery of the outer case T T. The arrow shows the direction of
rotation. The air is thus sent out by the apertures a a. O is the

(b) The air-blast has also been used by Prof. Thomson in experiments
with high frequency currents of high potential. By directing a blast of
air against a spark discharge between ball terminals of an alternating
current, the nature of the current was changed and it became capable of
producing most extraordinary effects by induction.



Air Condenser.
A static condenser whose dielectric is air. The capacity of an air
condenser in farads is equal to
  A / ( 4.452E12 * t )
in which A is the area of one sheet or sum of the areas of one set of
connected sheets in square inches and t is the thickness of the layer of
air separating them.

A convenient construction given by Ayrton consists in a pile of glass
plates P separated by little bits of glass F of known thickness, three
for each piece. Tin-foil T is pasted on both sides of each piece of
glass and the two coatings are connected. The tin-foil on each second
plate is smaller in area than that on the others. The plates are
connected in two sets, each set comprising every second plate. For A in
the formula the area of the set of smaller sheets of tin-foil is taken.
By this construction it will be seen that the glass does not act as the
dielectric, but only as a plane surface for attachment of the tin-foil.
Posts E E keep all in position. One set of sheets connects with the
binding post A, the other with B.

The capacity of any condenser with a dielectric of specific inductive
capacity i is given by the formula:
     ( i *A^1 ) / ( 4.452E12 * t1 )

The air condenser is used for determining the value of i for different



Air Gaps.
In a dynamo or motor the space intervening between the poles of the
field magnet and the armature. They should be of as small thickness, and
of as extended area as possible. Their effect is to increase the
magnetic reluctance of the circuit, thereby exacting the expenditure of
more energy upon the field. They also, by crowding back the potential
difference of the two limbs, increase the leakage of lines of force from
limb to limb of the magnet.

Air Line Wire.
In telegraphy the portion of the line wire which is strung on poles and
carried through the air.

Air Pump, Heated.
It has been proposed to heat portions of a mercurial air pump to secure
more perfect vacua, or to hasten the action. Heating expands the air and
thus produces the above effects.


Air Pump, Mercurial.
An air pump operated by mercury. The mercury acts virtually as the
piston, and the actuating force is the weight of the column of mercury,
which must exceed thirty inches in height. There are many types.
Mercurial air pumps are largely used for exhausting incandescent lamp
chambers. (See Geissler Air Pump,--Sprengel Air Pump.)

Air Pumps, Short Fall.
A mercurial air pump in which the fall of mercury or the height of the
active column is comparatively small. It is effected by using several
columns, one acting after the other. A height of ten inches for each
column suffices in some forms. Enough columns must be used in succession
to make up an aggregate height exceeding 30 inches.



Alarm, Burglar.
A system of circuits with alarm bell extending over a house or
apartments designed to give notice of the opening of a window or door.
As adjuncts to the system the treads of the stairs are sometimes
arranged to ring the bell, by completing a circuit when trod on. Door
mats are also arranged to close circuits in like manner.


For doors and windows switches are provided which are open as long as
the door or window is closed, but which, on being released by opening
the door or windows, automatically close the circuit. The circuit
includes an alarm bell and battery, and the latter begins to ring and
continues until stopped, either by the closing of the door or by a
switch being turned. The connections are sometimes so contrived that the
reclosing of the door or window will not stop the bell from ringing.

The cuts show various switches for attachment to doors and windows. It
will be seen that they normally keep the circuit closed, and that it is
only open when pressure, as from a closed door, is brought upon them. In
the case of a door a usual place for them is upon the jamb on the hinge
side, where they are set into the wood, with the striking pin
projecting, so that as the door is closed the pin is pressed in, thus
breaking the circuit.

Sometimes the connections are arranged so as to switch on the electric
lights if the house is entered. Special annunciators showing where the
house has been entered are a part of the system. A clock which turns the
alarm on and off at predetermined hours is also sometimes used.

The circuits may be carried to a central station or police station. One
form of burglar alarm device is the Yale lock switch. This is a contact
attached to a Yale lock which will be closed if the wrong key is used,
completing a circuit and ringing a bell.


Alarm, Electric.
An appliance for calling attention, generally by
ringing a bell. It is used to notify of water-level in boilers or tanks,
of entrance of a house, or of other things as desired. It is evident
that any number of alarms could be contrived.


Alarm, Fire and Heat.
An alarm for giving notice of the existence of a conflagration. Such are
sometimes operated by a compound bar thermostat (see Thermostat), which
on a given elevation of temperature closes a circuit and rings an
electric bell. Sometimes the expansion of a column of mercury when
heated is used. This, by coming in contact with one or two platinum
points, completes a circuit, and rings the bell.

The identical apparatus may be used in living rooms, greenhouses.
factories and elsewhere, to give an alarm when the temperature rises or
falls beyond predetermined limits.

Alarm, Overflow.
An alarm to indicate an overflow of water has been suggested on the
lines of a contact completed by water, or of the elements of a battery
which would be made active by water. Thus two sheets of metal might be
separated by bibulous paper charged with salt. If these sheets were
terminals of a circuit including a bell and battery, when water reached
them the circuit would be closed and the bell would ring. It was also
proposed to use one copper and one zinc sheet so as to constitute a
battery in itself, to be thrown into action by moisture. These contacts
or inactive batteries could be distributed where water from an overflow
would be most likely to reach them.

Alarm, Water Level.
An alarm operated by a change of water level in a tank or boiler. By a
float a contact is made as it rises with the water. Another float may be
arranged to fall and close a contact as the level falls. The closing of
the contacts rings an electric bell to notify the attendant in charge.

Alcohol, Electrical Rectification of.
A current of electricity passed through impure alcohol between zinc
electrodes is found to improve its quality. This it does by decomposing
the water present. The nascent hydrogen combines with the aldehydes,
converting them into alcohols while the oxygen combines with the zinc

The placing in or occupying of the same straight line. The bearings of a
shaft in dynamos, engines, and other machinery have to be in accurate

The power of existing in several modifications possessed by some
substances, notably by chemical elements. Instances of the allotropic
state are found in carbon which exists as charcoal, as graphite
(plumbago or black lead), and as the diamond. All three are the same
elemental substance, although differing in every physical and electrical


A mixture, produced almost universally by fusion, of two or more metals.
Sometimes alloys seem to be chemical compounds, as shown by their having
generally a melting point lower than the average of those of their
constituents. An alloy of a metal with mercury is termed an amalgam. An
important application in electricity is the use of fusible alloys for
fire alarms or for safety fuses. German silver is also of importance for
resistance coils, and palladium alloys are used for unmagnetizable
watches. An alloy of wrought iron with manganese is almost
unmagnetizable, and has been proposed for use in ship building to avoid
errors of the compass.

Alloys or what are practically such can be deposited by electrolysis in
the electro- plater's bath. We give the composition of some alloys
interesting to the electrician.

  Solder:   Lead   1 part   Tin   2 parts
             "      "       "    1  "
             "      "       "    2  "

German Silver: Copper, 2 parts; Nickel, 1 part;
               Zinc, 1 part (used for resistances).

Platinum, Silver Alloys: Platinum, 1 part;
                         silver, 2 parts (used for resistances.)

Palladium alloys for watch springs. (See Palladium.)

Alphabet, Telegraphic.
The combinations of sounds, of dots and dashes marked on paper, of
right-hand and left-hand deflections of a needle, of bells of different
notes, or of other symbols by which a fixed combination is expressed for
each character of the alphabet, for numerals, and for punctuation. While
the code is designed for telegraphic uses it can be used not only for
the conveyance of signals and messages by the electrical telegraphs, but
also by any semaphoric or visual system, as by flashes of light,
movements of a flag or even of the arms of the person signalling.

In the English and continental needle telegraphy in which the message is
transmitted by the movements of an index normally vertical, but
oscillating to one side or the other under the influence of the current,
the latter being controlled by the transmitter of the message, the left
hand swings of the needle are interpreted as dots, the right hand as

This system enables one alphabet to be translated into the other, or
virtually one alphabet answers for both Morse and needle transmitters.

There are two principal telegraphic alphabets, the American Morse and
the International codes. They are very similar, their essential
distinction being that spaces are used in the American code, while they
are excluded from the International code.

In the American Morse system the message is now universally received by
sound. (See Sounder--Sound Reading.)


The two codes or telegraphic alphabets are given here.

     Parenthesis,             - . - - . -
  Understand,              ... - .
  I don't understand,      ..-- ....--..
  Wait,                    .-. . .
  Erase,                   ...   ...   ...
  Call signal,             -.-.-.-
  End of message,          .-.-.-.
  Cleared out all right,   .-..-..-.
  A  .-    L  .-..  W  .--
  B  -...  M  --    X  -..-
  C  -.-.  N  -.    Y  -.--
  D  -..   O  ---   Z  --..
  E  .     P  .--.
  F  ..-.  Q  --.-  Ch ----
  G  --.   R  .-.   Ä  .-.-
  H  ....  S  ...   Ö  ---.
  I  ..    T  -     Ü  ..--
  J  .---  U  ..-   É  ..-..
  K  -.-   V  ...-  Ñ  --.--

  1  .----  4  ....-  8  ---..
  2  ..---  5  .....  9  ----.
  3  ...--  6  -....  0  -----
            7  --...

[Transcriber's note: The original image of the dot/dash pattern is somewhat
ambiguous. Since there may be differences from contemporary specifications,
the original image is included.]




  Period (.)         ...   ...
  Comma (,)          .-.-.-
  Query(?)           ..--..
  Exclamation (!)    --..--
  Apostrophe (')     .----.
  Hyphen (-)         -....-
  Fresh paragraph,   .-.-..
  Inverted commas,   -..-.

  A  .-       L  ----(Continuous)  W  .--
  B  -...     M  --                X  .-..
  C  ..s.     N  -.                Y  ..s..
  D  -..      O  .s.               Z  ….
  E  .        P  .....
  F  .-.      Q  ..-.              Ch ----
  G  --.      R  .s..              Ä  .-.-
  H  ....     S  ...               Ö  ---.
  I  ..       T  -                 Ü  ..--
  J  - . - .  U  ..-               É  ..-..
  K  -.-      V  ...-              Ñ  --.--

  1  .--.    4  ....-     8  -....
  2  ..-..   5  ---       9  -..-
  3  ...-.   6  ... ...   0  -----(Continuous)
             7  --..

[Transcriber's Note: The "s" in the American Code indicates a "space". I
leave the following to the reader's imagination. See the original

Comma (,)
Semicolon (;)
Colon (:)
Colon Dash (:~)
Period (.)
Interrogation (?)
Exclamation (!)
Dash (-)
Hyphen (-)
Pound Sterling (£)
Shilling Mark ( )

[Image of page 21: THE AMERICAN ALPHABET.]


[Transcriber's Note: I leave these to the reader's imagination. See the
following original image.]

Dollars ($)
Decimal Point (.)
Cents (c)
Paragraph ()
Pence (d.)
Fractional Mark (--)
Capitalized Letter
Italics or Underline
Colon followed by Quotation :"
Parenthesis (   )
Brackets [   ]
Quotation Marks " "
Quotation within a Quotation " ' ' "

[Image of page 22: THE AMERICAN ALPHABET.]

The principal differences in the two codes are the use of spaces in the
American code, such being excluded from the International code. This
affects the letters C, R, Y, & Z.

The following diagram, due to Commandant Perian, enables the letter
corresponding to an International code sign to be rapidly found with the
exception of R.

             <- dot       start         dash   ->
               /                           \
              E                             T
         /          \                /             \
       I              A             N                M
    /    \          /    \        /    \         /      \
   S      U        R      W       D      K       G       O
 /  \    / \     / \    /  \    /  \     /  \    /  \    /  \
H   V   F   U   L   A   P   J   B   X   C   Y   Z    Q  Ô   CH

Fig. 10. Diagram for translating the Morse Alphabet.

In order to find what letter corresponds to a given sign, starting from
the top of the diagram, each line is traced down to a bifurcation,
taking the right hand line of each bifurcation for a dash, and the left
hand line for a dot, and stopping when the dots and dashes are used up.
Thus, for example,

the signal -.- -   leads us to the letter d,

the signal - - - - to the letter j and so on.


Alternating. adj.
Term descriptive of a current changing periodically in
direction. (See Current, Alternating.)


Alternating Current Arc.
The arc produced by the alternating current. It presents several
peculiarities. With an insufficient number of alternations per second it
goes out. As the carbons wear away equally it is adopted for such lamps
as the Jablochkoff candle, (see Candle, Jablochkoff). As no crater is
formed the light is disseminated equally both up and down. For this
reason to get full downward illumination a reflector is recommended.

Alternating Current System.
A system of electric distribution employing the alternating current. For
transmission in the open air or in conduits a high potential circuit is
used, from 1,000 to 10,000 volts being maintained at the central
station. Two leads unconnected at the end lead from the station. Where
current is desired a converter or transformer (see Converter) is placed,
whose primary is connected to the two leads bridging the interval
between them. From the secondary the house leads are taken with an
initial potential in some cases of 50 volts. The converters are thus all
placed in parallel. By law or insurance rules the converters are
generally kept outside of buildings. Where no secondary current is taken
from the converters very little primary current passes them on account
of their counter-electromotive force. As more secondary current is taken
the primary increases and this accommodation of one to the other is one
of the interesting and valuable features. Street lamps are sometimes
connected in series. Each lamp in such case is in parallel with a small
coil with iron core. While the lamp is intact little current passes
through the coil. If the lamp is broken, then the converter impedes the
current by its spurious resistance, q. v., just enough to represent and
replace the resistance of the extinguished and broken lamp filament.
(See Meter, Alternating Current; Motor, Alternating Current.)

The change in direction of a current. The number of such changes is
expressed as number of alternations; thus a current may have a frequency
of 500 or 20,000 alternations per second.

[Transcriber's note: One alternation per second is now called one hertz.]

Alternation, Complete.
A double alternation; a change from one direction
to the other and back again to the original phase. A symbol derived from
its graphic representation by a sine curve is used to indicate it. The
symbol is  ~


Alternative Path.
A second path for a current appearing as a disruptive
discharge. Where two paths are offered the discharge, as it is of
alternating or oscillatory type, selects the path of least
self-induction. Thus a thick bar of copper, with no air gap, may be
abandoned by the current in favor of a small iron wire with an air gap,
but which has less self-induction.

The lightning arresters, q. v., for the protection of telegraph offices
are sometimes based on these principles. A path of very high resistance
but of small self-induction is offered between the line and the earth.
This the lightning discharge selects in preference to the instruments
with their iron cores, as the latter are of very high self-induction.

A dynamo electric generator supplying an alternating current. (See
Dynamo, Alternating Current.)

Synonym--Alternating current generator or dynamo.

Alternator, Constant Current.
An alternating current dynamo supplying a current of unvarying virtual
amperage. Alternators of this type are constructed with an armature of
high self-induction. Sometimes fine winding contained in deep peripheral
notches in the core-discs is employed to magnify the self-induction.
Such generators are employed for series lighting, especially

A metal; one of the elements; symbol: Al.
Atomic weight: 27.4. Equivalent: 9.13. Valency: 3.
Specific gravity: 2.6. It is a conductor of electricity.
Relative resistance annealed, (Silver = 1)  1.935
Specific resistance at 0ºC (32°F.)    2.912 microhms

Resistance of a wire at 0ºC  (32°F.)
a) 1 foot long, weighing 1 grain,     0.1074 ohms.
b) 1 foot long, 1/1000 inch thick,   17.53     "
c) 1 meter long, weighing 1 gram,     0.0749   "
d) 1 meter long, 1 millimeter thick   0.03710  "
Resistance of a 1-inch cube at 0ºC (32°F.) 1.147 microhms
Electro-chemical equivalent.    .0958 (hydrogen == .0105)


(a) A combination or alloy in which one of the constituents is mercury.
Usually the term is applied to an alloy of a single metal with mercury.
Some metals readily form amalgams; such metals are: Gold, zinc, silver,
lead and others; some, such as platinum and iron, form amalgams only
under exceptional circumstances.

(b) The word is also applied to compositions for application to the
cushions of frictional electric machine in which cases it is often a
misnomer. True amalgams used for this purpose are made as follows:

(a) Tin, 1 part;  Zinc, 1 part;  Mercury, 2 parts (Kienmayer).
(b) Tin, 2 parts; Zinc, 3 parts.
(c) Tin, 3 parts; Zinc, 5 parts; Mercury, 4 parts.
(d) Zinc, 1 part: Mercury, 4 parts; Mercury, 9 parts.  [sic]

The tin, if such is used, (formula a, b and c) is first melted, the zinc
is added in successive portions. The mercury, which must be heated, is
slowly poured into the melted alloy after removal of the latter from the
fire, and the mixture, while making, is constantly stirred. It is kept
stirred or rubbed in a mortar until cold. Sometimes it is poured into
water and kept in constant agitation until cold. It is thus obtained in
a granular condition, and is pounded in a mortar until reduced to
powder. It must be dried and kept in tightly stopped bottles and is
applied to the cushions after they have been greased. It is to be
noticed that it is said that alloy (d) requires no pulverization beyond
constant rubbing in a mortar as it cools. Sometimes the amalgam is
shaken about in a wooden tray with chalk while cooling. The action of
amalgams is not very clearly understood. Some claim that there is a
chemical action, others that they simply act as conductors, others that
they are more highly negative to the glass than the leather of the

Graphite or sulphide of tin (mosaic gold) are sometimes used to coat the
cushions; it is these that are sometimes incorrectly called amalgams.

The application of mercury to a metal with which it forms an amalgam, or
with which it amalgamates. Battery zincs are amalgamated in two ways. In
the immersion method, the plate is dipped into an acid solution of
mercuric chloride or nitrate. The latter is best. In the direct
application method the plate is first wet all over with dilute acid and
a little mercury is dropped upon it and is rubbed over the surface with
a rag or, what is better, with a piece of galvanized iron. A very little
mercury answers the purpose. The whole surface of the plate should be
left as bright as silver. (See Action, Local.)

Amber is a fossil resin, supposed to be a product of the extinct Pinites
Succinifer and other coniferous trees. Most of it is gathered on the
shores of the Baltic between Koenigsberg and Memel. It is also found in
small pieces at Gay Head, Mass., and in New Jersey green sand. It is
found among the prehistoric remains of the Swiss Lake dwellers. When
rubbed with a cloth it becomes excited with negative electricity. The
Greek word for it is electron, which gave the name electricity to the
modern science. Thales of Miletus, 600 B. C., and Theophrastus, about
300 B. C., both mention its electric properties or power of attracting
small objects when rubbed.


The commercial name for an ampere-meter, an instrument designed
to show by direct reading the number of amperes of current which are
passing through a circuit.

A great variety of ammeters have been invented, based on different
principles. The definitions following this one give some idea of the
lines of construction followed.

Synonym--Ampere meter.

Ammeter, Ayrton's.
A direct reading instrument for measuring current intensity.

A solenoid receives the current. In the axis of the solenoid an iron
tube is suspended by a long spiral spring that passes down within it,
and the upper end of which spring is fastened to the glass top of the
instrument. The tube is provided with proper guides so as to maintain a
vertical position, and is free to rotate. Its upper end carries an

The whole operates as a magnifying device. A slight longitudinal
displacement of the tube causes it to rotate through a considerable
angle by the action of the spring. By properly proportioning the parts,
the angle of displacement of the index is directly proportional to the
current between 15º and 270º angular displacement.

The same instrument is wound for use as a volt-meter.

Its principal fault is its restricted range.

Ammeter, Commutator.
A commutator ammeter is one whose windings consist of separate strands,
each of any desired number of turns, and provided with a commutating
attachment for throwing them into series or into parallel as desired.
The essential condition is that all the wires shall be of equal
resistance and of equal number of turns. Such an instrument can be used
for heavy or light currents. Two sets of graduations are marked on its
scale if it is a calibrated instrument. (See Calibration.) Commutator
volt-meters are constructed on the same principle.

Ammeter, Cunynghame's.
A modification of the Siemens' electro-dynamometer. (See
Electro-dynamometer, Siemens'.) An electro-magnet with very massive core
is excited by the current. As the core is of small reluctance the
strength of the magnet is nearly proportional to the current strength.
Between the poles of the magnet a soft iron armature or induced magnet
is pivoted. It carries a pointer so adjusted that when the axis of the
soft iron magnet is at an angle of about 30º with the line joining the
poles of the electro-magnet the pointer will indicate zero.

The soft iron armature is so massive that the magnetism induced in it is
proportional to the strength of the electro-magnet. Hence the couple
exerted by the electro-magnet on the pivoted armature will be
proportional to the square of the current.

The armature is retained in place by a spiral spring lying in line with
its axis of rotation. The instrument is operated as a zero reading
instrument. The current is passed through it. The needle is deflected;
it is brought back to zero by turning a milled head which twists the
spring. The current will be proportional to the square root of the angle
of displacement of the milled head. A scale with index is provided,
giving directly the square roots of the angle over which the pointer is

The same instrument is wound for use as a volt-meter.


Ammeter, Eccentric Iron Disc.
This ammeter comprises a cylindrical electro-magnet excited by the
current to be measured. A disc of iron free to rotate is suspended on
pivots below it. A piece is cut off the disc at one part of its
periphery so as to give more metal to one side than to the other. In its
zero position this portion of the disc swings towards the magnet. As the
latter is more and more excited the other or more projecting portion of
the disc turns towards it, being attracted like an armature, and moves
against the force of gravity, the disc rotating. An index attached to
the disc swings over the face of a graduated scale. The disc is so
counterpoised that in its natural position the index points to zero.

Ammeter, Electro-magnetic.
An ammeter depending for its working upon the action of an
electro-magnet, which is excited by the current to be measured.

Ammeter, Gravity.
An ammeter whose hand or index is drawn into the zero position by
gravity, and whose displacement therefrom is produced by the action of
the current to be measured.


Ammeter, Magnetic Vane.
A fixed plate of soft iron is placed within a coil. Facing it is a
second disc free to move or swing on an axis. When the field is excited
the two repel each other because like polarity is induced in each, and
the motion of the movable disc indicates the strength of the current.
The same instrument is wound for high resistance and constitutes a
Magnetic Vane Voltmeter.


Ammeter, Magnifying Spring.
A solenoid ammeter in which a spiral spring is used to convert the
longitudinal motion of the armature or movable core into a rotary motion
(see Ammeter, Ayrton's) and magnify the apparent range of motion.

Ammeter, Permanent Magnet.
An ammeter with a magnetic field produced by a permanent magnet.

Ammeter, Solenoid.
An ammeter in which the attraction, when a current is passing through
it, exerted by a hollow coil of wire upon an iron bar or tube in line
with its axis, is utilized to indicate the strength of current. The bar
is drawn into the coil to different extents proportional to the
attraction. As an example see Ammeter, Ayrton's, and cut of Gravity

Ammeter, Spring.
An ammeter in which the part moved by the current is controlled or
brought to the zero position by a spring.

Ammeter, Steel Yard.
A solenoid ammeter in which the solenoid core is suspended vertically
from the short end of a steel yard fitted with a sliding weight. The
current passes through the solenoid coil and attracts or draws downwards
the coil. A sliding weight is moved in and out on the long steel-yard
arm which is graduated for amperes. In use the weight is slid out until
the arm is in equipose; the divisions give the amperes.



Ammunition Hoist, Electric.
An apparatus for use on ships for hoisting ammunition to the guns by an
electric elevator. The characteristic feature of it is that a constant
motion of the switch or handle is required to keep it in action. If the
operator is shot so as to be incapacitated from taking charge of the
switch, the hoist stops until another is assigned to it.

Current intensity expressed in amperes, as an amperage of ten amperes.

The practical unit of electric current strength. It is the measure of
the current produced by an electro-motive force of one volt through a
resistance of one ohm. In electric quantity it is the rate of one
coulomb per second. It is one-tenth the absolute C. G. S. unit of
current strength. Its best analogy is derived from water. Assuming the
electric current to be represented by a current of water, the pressure,
head, or descent producing such current would be the electro-motive
force. The current might be measured in gallons (or other unit) passed
per second. In the analogy these gallons would be coulombs. But it might
be measured by reference to a standard stream, as for instance, the
stream which would pass through a hole an inch square under a given
head, say six inches of water. This unit is the miner's inch, and is the
exact analogy of the ampere. A current of water may flow at the rate of
so many miner's inches, just as a current of electricity may flow at the
rate of so many amperes. In neither case it will be noted is there any
reference to time. "An ampere per second" is a redundant expression, and
means no more than "an ampere"; an "ampere-second," on the other hand,
is a coulomb. The number of coulombs passed per second gives the amperes
of current.

For value of ampere, see Coulomb.

[Transcriber's note: The SI definition of an ampere: A current in two
straight parallel conductors of infinite length and negligible
cross-section, 1 metre apart in vacuum, would produce a force equal to
2E-7 newton per metre of length.]



Ampere, Arc.
A conductor bent into the arc of a circle, and employed in measuring the
electric current by the electric balance.

The currents assumed to be the cause of magnetism. (See Magnetism,
Ampere's Theory of.)

The product of amperes of current by the length, in feet, of a conductor
passing such current. It may be in empiric calculations of dynamo or
motor construction, but is little used. One ampere-foot is a current of
one ampere passing through one foot length of a conductor, or one-tenth
ampere through ten feet, and so on.

The quantity of electricity passed by a current of one ampere in one
hour. It is used by electric power and lighting companies as the unit of
energy supplied by them, because they maintain a constant potential
difference in their leads, so that only the amperes and hours need
measuring or recording to give the energy, viz. : volt-ampere-hours.
The same unit is applied to batteries to indicate their potential
energy, because they also are assumed to be of constant voltage or
electro-motive force.

The product of amperes of current by the length, in meters, of a
conductor carrying such current. One ampere-meter is a current of one
ampere passing through one meter of a conductor.

The term must not be confused with the identically spelled Ampere-meter,
a synonym for Ammeter.

The quantity of electricity passed by a current of one ampere in one
minute; sixty coulombs.

Ampere Ring.
A conductor forming a ring or circle used in electric balances for
measuring currents. (See Balance, Ampere.)

The quantity of electricity passed by a current of one ampere in one
second; the coulomb, q. v.

Amperes, Lost.
In a shunt or compound-wound dynamo, part of the total amperes of
current produced in the armature coils go through the shunt, and hence,
do not appear in the outer circuit. S. P. Thompson has proposed the term
"lost amperes" for this portion of the current.

Ampere's Memoria Technica.
An expression of the effect of a current on a magnetic needle. If we
imagine the observer in the line of the current and facing the magnetic
needle, the current entering by his feet and leaving by his head, the
north pole is deflected to his left.


The amperes of current supplied to a magnet coil multiplied by the
number of turns the current makes in the coil. If the coil is wound two
or three in parallel, the virtual turns by which the amperes are
multiplied are one-half or one-third the actual turns of wire.

Synonym--Ampere Windings.

Ampere-turns, Primary.
The ampere-turns in the primary coil of an induction coil or

Ampere-turns, Secondary.
The ampere-turns in the secondary coil of an induction coil or

Amplitude of Waves.
Waves are distinguished by length and amplitude. The latter, in the case
of transverse waves, such as those of water and of the ether, correspond
with and measure the height from lowest to highest point, or from valley
to summit of the waves in question. In the case of longitudinal waves,
such as those of the air, due to sounding bodies, the ratio of degree of
rarefaction to degree of condensation existing in the system is the
amplitude. The latter can be graphically represented by a sinuous line,
such as would represent the section of a transverse wave. Ether waves
are produced by heated bodies and by electro-magnetic impulses, as in
the discharge of the Leyden jar.

The amplitude of a wave, other things being equal, is the measure of its
intensity. Thus, the louder a sound the greater is the amplitude of the
system of waves to which it is due. The same applies to ether waves,
whether they are perceived in the electro-magnetic, light, or
heat-giving modification. As the amplitude of ether waves cannot be
accurately known, amplitude is a relative term and is not stated
generally in any absolute unit.

Analogous Pole.
One of the elements of a pyro-electric crystalline substance, such as
tourmaline. When heated, such bodies acquire electrical properties. If
of such crystalline form that they are differently modified at the ends
of their crystalline axis, by hemihedral modifications, the ends may be
differently affected. One end may show positive electricity when the
temperature is rising, and negative when falling. Such end is then
called the analogous pole. The opposite end presents, in such cases, the
opposite phenomena; becoming negative when the temperature is rising,
and becoming positive when it is falling; such end is called the
antilogous pole.

The determination of the elements of a case. It may be chemical, and
consist in finding what a substance consists of; it may be mathematical,
and consist in determining the unknown quantities in a problem; or it
may belong to other branches of science. The term has a very extended
application. Where the constituents are only determined in kind it is
called qualitative analysis; where their quantity or percentage is
ascertained it is called quantitative analysis.


Analysis, Electric.
Chemical analysis by electrolytic methods. (See Electrolytic  Analysis.)

Analyzer, Electric.
An apparatus used in investigations on electric ether waves. It consists
of a series of parallel metallic wires. When the electric waves have
been polarized, the analyzer will only permit them to go through it
intact, when the plane of vibration of the waves is parallel to its

(a) Bodies which do not become electrified by friction; a term
introduced by Gilbert, now little used, as all bodies develop
electricity under proper conditions by contact action; the reverse of

(b) Also a conductor of electricity, the reverse of a dielectric, q. v.
(See Conductor.)

It will be seen that Gilbert's anelectrics were, after all, the same as
the modern anelectrics, i.e., conductors.

A term used in medical electricity or electro-therapeutics to indicate
the deceased functional activity induced in a nerve by the proximity of
the anode of an active electric circuit completed through the nerve. The
converse of Kathelectrotonus.

Angle of Declination.
The angle of error of the magnetic needle or compass, measuring the
extent of its deviation from the meridian in any locality. It is the
angle between the plane of the magnetic axis of a magnetic needle free
to take its natural position, and the geographical meridian, the needle
being counterpoised if necessary, so as to hold an absolutely horizontal
position. The deviation is expressed as being east or west, referring
always to the north pole. (See Magnetic Elements.)

Synonym--Variation of the Compass.

[Transcriber's note:  See Agonic Line.]

Angle of the Polar Span.
In a dynamo or motor the angle subtended by the portion of a pole piece
facing the armature, such angle being referred to the centre of the
cross-section of the armature as its centre.


Angular Velocity.
The velocity of a body moving in a circular path, measured with
reference to the angle it passes over in one second multiplied by the
radius and divided by the time. A unit angle is taken (57°.29578 =
57° 17' 44".8 nearly) such that it is subtended by a portion of the
circumference equal in length to the radius. Hence, the circumference,
which is 360°, is equal to 2*PI*unit angle, PI being equal to 3.1416--.
"Unit angular velocity" is such as would in a circle of radius = 1
represent a path = 1, traversed in unit time = 1 second. If the radius
is r and the angle passed over is theta, the distance is proportional to
r*theta; if this distance is traversed in t seconds the angular velocity
is theta / t. The angular velocity, if it is multiplied by r, theta
expressing a distance, will give the linear velocity. The dimensions of
angular velocity are an angle (= arc / radius) / a Time = (L/L)/T =

The velocity expressed by the rate of an arc of a circle of unit radius,
which arc subtends an angle of 57° 17' 44".8, such arc being traversed
in unit time, is unit angular velocity.

Animal Electricity.
Electricity, notably of high tension, generated in the animal system, in
the Torpedo, Gymnotus and Silurus. The shocks given by these fish are
sometimes very severe. The gymnotus, or electric eel, was elaborately
investigated by Faraday. It has the power of voluntarily effecting this
discharge. There is undoubtedly some electricity in all animals. The
contact of the spinal column of a recently killed frog with the lumbar
muscles produces contraction, showing electric excitement. Currents can
be obtained from nerve and muscle, or from muscle sides and muscle cut
transversely, in each case one thing representing positive and the other
negative elements of a couple.

Angle of Inclination or Dip.
The angle which the magnetic axis of a magnet, which magnet is free to
move in the vertical plane of the magnetic meridian, makes with a
horizontal line intersecting such axis. To observe it a special
instrument, the dipping compass, inclination compass, dipping needle, or
dipping circle, as it is called, is used. (See Elements, Magnetic,
--Dipping Needle,--Compass, Inclination.)

Angle of Lag.
The angle expressing the displacement of the magnetic axis of the
armature core of a dynamo in the direction of its rotation. (See Lag.)
Lag is due to the motion of the armature core.

Angle of Lead.
The angle expressing the displacement in the direction of rotation of
the armature of a dynamo which has to be given the brushes to compensate
for the lag. (See Lag.) This is positive lead. In a motor the brushes
are set the other way, giving a negative angle of lead or angle of
negative lead.

The electro-negative element or radical of a molecule, such as oxygen,
chlorine or the radical sulphion. (See Ions.) It is the portion which
goes to the anode, q.v., in electrolytic decomposition.


Anisotropic. (adj.)
Unequal in physical properties, as in conduction and specific inductive
capacity, along various axes or directions. An anisotropic conductor is
one whose conductivity varies according to the direction of the current,
each axis of crystallization in a crystalline body marking a direction
of different conductivity. An anisotropic medium is one varying in like
manner with regard to its specific inductive capacity. In magnetism an
anisotropic substance is one having different susceptibilities to
magnetism in different directions. The term is applicable to other than
electric or magnetic subjects.


Annealing, Electric.
Annealing by the heat produced by the passage of the electric current
through the body to be annealed. The object is clamped or otherwise
brought into a circuit, and a current strong enough to heat it to
redness, or to the desired temperature is passed through it.

An apparatus for announcing a call from any place to another, as from a
living-room to an office in a hotel, or for announcing the entering of
any given room or window in a building protected by a burglar alarm.

A usual system comprises for each annunciator an electro-magnet. Its
armature is normally held away from its poles by a spring, and when in
that position a latch connected to the armature holds a little shutter.
When by a push-button or other device a current is sent through a
circuit which includes the electro-magnet the armature is attracted,
this releases the latch and the shutter drops. In dropping it displays a
number, letter or inscription which indicates the locality of the
push-button or other circuit-closing device. Often annunciators are
connected in circuit with a bell.



Annunciator Clock.
A clock operating an annunciator by making contact at determined times.

Annunciator Drop.
The little shutter which is dropped by some forms of annunciators, and
whose fall discloses a number, character or inscription, indicating
whence the call was sent.



Annunciator, Gravity Drop.
An annunciator whose operations release shutters which fall by gravity.

Annunciator, Needle.
A needle annunciator is one whose indications are given by the movements
of needles, of which there is usually a separate one for each place of

Annunciator, Swinging or Pendulum.
An annunciator which gives its indications by displacing from its
vertical position a pendulum or vertically suspended arm.


Anodal Diffusion.
A term in electro-therapeutics; the introduction of a medicine into the
animal system by using a sponge-anode saturated with the solution of the
drug in question. On passing a current the desired result is secured by
cataphoresis, q. v.

The positive terminal in a broken metallic or true conducting circuit;
the terminal connected to the carbon plate of a galvanic battery or to
its equivalent in case of any other generator. In general practice it is
restricted to the positive terminal in a decomposition or electrolytic
cell, such as the nickel anode in a nickel-plating bath or the anode of
platinum in a gas voltameter. It is the terminal out of or from which
the current is supposed to flow through the decomposition cell. In
electro-therapeutics the term is used simply to indicate the positive
terminal. In an electrolytic cell the electro-negative substance or
anion goes to the anode. Hence, it is the one dissolved, if either are
attacked. The nickel, copper or silver anodes of the electroplater
dissolve in use and keep up the strength of the bath. The platinum anode
in a gas voltameter is unattacked because the anion cannot act upon it

Anodic Closure Contraction.
A physiological change in a living subject produced by the closing of
the electric current; the muscular contraction which takes place beneath
the anode applied to the surface of the body when the circuit is closed,
the kathode being applied elsewhere; it is due, presumably, to direct
action on the motor nerve. It is a term in electro-therapeutics. It is
the converse of anodic opening contraction, q. v. An abbreviation A. C.
C. is often used to designate it.

Anodic Duration Contraction.
A term in electro-therapeutics. On the opening or closing of an electric
circuit, the anode of which is placed over a muscle, a contraction is
observed (see Anodic Closure Contraction--Anodic Opening Contraction).
The above term is used to designate the duration of such contraction. An
abbreviation A. D. C. is often used to designate it.

Anodic Opening Contraction.
The converse of Anodic Closure Contraction, q. v.; it is the contraction
of living muscle beneath or near the anode where the circuit, including
such anode and the body in its course, is closed; a physiological
phenomenon observed in electro-therapeutics to which branch of science
the term belongs. An abbreviation A. O. C. is often used to designate

Anodic Reactions.
A term in electro-therapeutics; the diagnosis of disease by the actions
of the tissue near the anode of a circuit.

Anti-Induction Conductor.
A conductor constructed to avoid induction effects in the conducting
element. Many kinds have been made. A tubular metal shield or envelope
which may be grounded will protect an enclosed conductor to some extent.
Or the conductor may be a double wire twisted around itself, one branch
being used for the regular and the other for the return circuit, thus
constituting a closed metallic circuit. The inductive effects are due to
interrupted or varying currents in neighboring wires and circuits. Many
anti-induction conductors have been invented and patented.


Anti-magnetic Shield.
In general terms a hollow screen of soft iron designed to protect any
mass of steel behind or enclosed by it from magnetization by any magnet
near it, such as a dynamo field magnet. This it does by concentrating
the lines of force within its own mass, so that the space within it or
enclosed by it is comparatively free from lines of force. It is often
applied to watches, and is virtually an iron case in which they are

A metal, one of the elements, atomic weight, 122:
equivalent, 40.6 and 24.4; valency, 3 and 5;
specific gravity, 6.8.
It is a conductor of electricity.
Relative resistance, compressed (silver = 1), 23.60
Specific resistance,   35.50 microhms.
Resistance of a wire,
(a) 1 foot long, weighing 1 grain,       3.418 ohms.
(b) 1 foot long, 1/1000 inch thick,    213.6     "
(c) 1 meter long, weighing 1 gram,       2.384   "
(d) 1 meter long. 1 millimeter thick,    0.4521  "

Resistance of a 1-inch cube,   13.98 microhms.

Approximate percentage resistance per degree C.
(1.8º F. at 20º C. 88º F.)   0.389 per cent.

Elcctro-chemical equivalent (hydrogen = .0105)  .2560
(See Thermo-Electric Series.)

An intermittent contact, or "make and break" of the current is sometimes
produced by directly pressing a key down upon a metallic surface, the
two being terminals of the circuit. The surface or stud on which such
pressure is produced is called the anvil. The ordinary telegraph key,
which makes a contact by the pressure of the operator's fingers does it
by making a contact between a contact piece upon the front end of the
key and the anvil. In the induction coil the anvil is also found. Thus
in the cut representing the end of an induction coil and its circuit
breaker in which O and O' and P and P' represent the secondary circuit
terminal connections A is the core of soft iron wires, h is the anvil;
the hammer when resting upon it so as to be in contact closes the
circuit. When the current coming from the primary to the post i, passes
through the hammer and anvil h, and emerges by m, it magnetizes the
core; this attracts the hammer, which is made of or is armed with a mass
of iron. This breaks the circuit. The hammer falls at once on the anvil,
again making the circuit, and the action is repeated with great
rapidity. Hammer and anvil or key and anvil connections should be made
of platinum.



A. O. C.
Abbreviation for Anodic Opening Contraction, q. v.

Aperiodic. adj.
In an oscillating apparatus, or in the oscillating member of apparatus,
the fact of having no reference to time of vibration; dead-beat.

Synonym. Dead-beat.


Fig. 18. ARAGO'S DISC.

Arago's Disc.
An apparatus consisting of a disc of copper mounted horizontally, or on
a vertical spindle, and so arranged as to be susceptible of rapid
rotation. Immediately over it, and best with a pane of glass
intervening, a magnetic needle is mounted on a pivot directly over the
axis of the disc. If the disc is rotated the lines of force of the
magnet are cut by it, and consequently currents are produced in the
copper. These currents act upon the needle and cause it to rotate,
although quite disconnected. It is advisable for the needle to be strong
and close to the disc, which should rotate rapidly.

Arc v.
To form a voltaic arc.

Arc, Compound.
A voltaic arc springing across between more than two electrodes.

Arc, Metallic.
The voltaic arc produced between terminals or electrodes of metal. The
characteristics of such arc as contrasted with the more usual arc
between carbon electrodes are its greater length for the same
expenditure of energy, its flaming character and characteristic colors
due to the metals employed. It is sometimes, for the latter reason, used
in spectroscopic investigations.

Arc Micrometer.
A micrometer for measuring the distance between the electrodes of a
voltaic arc.

Arc, Simple.
A voltaic arc produced, as usual, between only two electrodes.


Arc, Voltaic.
The voltaic arc is the arc between two carbon electrodes slightly
separated, which is produced by a current of sufficient strength and
involving sufficient potential difference. The pencils of carbon are
made terminals in a circuit. They are first placed in contact and after
the current is established they are separated a little. The current now
seems to jump across the interval in what sometimes appears an arch of
light. At the same time the carbon ends become incandescent. As regards
the distance of separation with a strong current and high electro-motive
force, the arc may be several inches long.

The voltaic arc is the source of the most intense heat and brightest
light producible by man. The light is due principally to the
incandescence of the ends of the carbon pencils. These are differently
affected. The positive carbon wears away and becomes roughly cupped or
hollowed; the negative also wears away, but in some cases seems to have
additions made to it by carbon from the positive pole. All this is best
seen when the rods are slender compared to the length of the arc.

It is undoubtedly the transferred carbon dust which has much to do with
its formation. The conductivity of the intervening air is due partly,
perhaps, to this, but undoubtedly in great measure to the intense
heating to which it is subject. But the coefficient of resistance of the
intervening air is so much higher than that of any other part of the
circuit that an intense localization of resistance occurs with
corresponding localization of heating effect. This is the cause of the
intense light. Thus if the carbons are but 1/32 of an inch apart as in a
commercial lamp the resistance may be 1.5 ohms. The poor thermal
conductivity of the carbon favors the concentration of heat also. The
apparent resistance is too great to be accounted for by the ohmic
resistance of the interposed air. A kind of thermoelectric effect is
produced. The positive carbon has a temperature of about 4,000° C.
(7,232° F.), the negative from 3,000° C. (5,432° F.) to 3,500° C.
(6,322° F.). This difference of temperature produces a
counter-electro-motive force which acts to virtually increase the
resistance of the arc. The carbon ends of an arc can be projected with
the lantern. Globules are seen upon them due to melted silica from the
arc of the carbon.



An instrument for determining the specific gravity of a fluid. It
consists of an elongated body ballasted so as to float vertically and
provided with a mark or a scale. It floats deeper in a light than in a
heavy liquid. If it carries but one mark weights are added until that
mark is reached, when the weights required give the specific gravity. Or
the scale may give the reading directly based upon the depth to which it
sinks. Areometers are often made of glass, ballasted with shot or
mercury enclosed in their bottom bulb as shown. They are used in
regulating battery solutions, and in watching the charging and
discharging of storage batteries.



Areometer, Bead.
A tube of glass containing beads of different specific gravities. It has
apertures at top and bottom. When immersed in a liquid, the same fills
it, and the specific gravity within certain limits, depending on the
factors of the beads, is shown by the beads which float and those which
sink. It is used for storage batteries and other purposes where acids
and solutions have to be tested.

The method of ascertaining the weight and inferentially the thickness of
an electroplater's deposit of silver. It is done by weighing the article
before and after plating.

The four members of a Wheatstone bridge, q. v., are termed its arms.
Referring to the diagram of a bridge, P, Q, R, S, are the arms.


(a.) A mass or piece of iron or steel, or a collection of pieces of iron
designed to be acted on by a magnet. While nickel or cobalt might be
used, they rarely or never are except in experimental apparatus. The
armature of a permanent horse shoe magnet is simply a little bar of soft
iron. When the magnet is not in use it is kept in contact with the poles
with the idea of retaining its magnetism. It is then said to be used as
a keeper. A bar magnet does not generally have an armature. The armature
is also used to exhibit the attraction of the magnet.

Sometimes an armature is made of steel and is permanently magnetized.
Such an armature, termed a polarized armature, is repelled when its like
poles are opposed to like poles of the magnet and otherwise is attracted
with force due to the sums of the magnetism. If the magnet is
sufficiently powerful depolarization of the armature may ensue when like
poles are opposed to like poles. Polarized armatures are used in various
appliances, magneto generators, telegraphic instruments and others.

(b) In a dynamo or Motor the mass of laminated iron or of wire which
carries the coils of insulated wires which are caused to rotate in the
field of force of the field magnets in order to establish and maintain
potential difference with its accompanying current, or which rotates
under the effects of a current in a motor. (See Dynamo Electric

The work of the armature core is twofold. It acts as a portion of the
magnetic circuit, conducting the lines of force, and by virtue of its
high permeability or multiplying power concentrating a number of the
lines of force through its own substance. To enable it to act with
efficiency in this direction it should be made of iron of the highest
permeability, and should approach as closely as possible to the armature
cores consistent with leaving space for the wire winding. It next acts
as a support for the wires which are to be swept through the field of
force. Thus it acts both to establish a strong field and then acts as a
carrier for the wires which are to be cut by the wires in question. In
connection with this subject the different definitions under Armature,
Dynamo, Commutator, Induction and similar topics may be consulted.

(c) See Armature of Influence Machine.

(d) See Armature of Leyden Jar or Static Condenser.


Armature, Bar.
An armature in a dynamo or motor whose winding is made up of conductors
in the form of bars, round, rectangular and of other sections. This type
of armature conductor is objectionable as Foucault currents are produced
in it. It is found best to laminate or subdivide low resistance armature

[Transcriber's Note: Foucault currents are also called eddy currents.]

Armature, Bipolar.
An armature in which two poles are induced by the field. A bipolar field
magnet produces a bipolar armature.

Armature Bore.
The cylindrical space defined by the pole pieces of a dynamo or motor
within which the armature rotates.

Synonym--Armature Chamber.


Armature, Closed Coil.
An armature for a motor or dynamo, the ends of all of whose coils are
united, so as to be in one closed circuit all the way around.


Armature Coil, or Coils.
The insulated wire wound around the core of the armature of an electric
current generator or motor.

Armature Core.
The central mass of iron on which the insulated wire, to be rotated in
the field of an electric current generator or motor, is wound. (See
Dynamo-electric Machine and Motor, Electric.)

Armature, Cylinder.
An armature of the Gramme ring type, but longer in the axial direction,
so that its core resembles a long hollow cylinder, the wire being wound
inside and outside as in the Gramme ring. (See Gramme Ring.)

Armature, Disc.
(a) An armature of a dynamo electric machine or motor in which the coils
are wound so as to be flat and are carried on the face of a disc forming
the core or part of the core of the armature. S. P. Thompson treats it
as a modified drum armature extended radially, the outer periphery
corresponding to the back end of the drum. The poles of the field are
generally placed to face the side or sides of the disc.

(b) Another type of disc armature has its wire wound on bobbins arranged
around the periphery of a disc.

In disc armatures there is often no iron core, their thinness enabling
this to be dispensed with.




Armature, Discoidal Ring.
In a dynamo an armature of the shape of a ring of considerable radial
depth of section as compared to its axial depth. It is generally made of
iron ribbon or thin band wound to the proper size.

Synonym--Flat Ring Armature.


Armature, Drum.
An armature for a dynamo or motor, consisting of a cylinder of iron
preferably made up of discs insulated from each other by thin shellacked
paper, or simply by their oxidized surfaces, and wound with wire
parallel to the axis where it lies on the cylindrical periphery and
crossing the heads approximately parallel to the diameter. It operates
practically on the same principle as a Gramme Ring Armature. (See Gramme

Synonym--Cylindrical Armature.

Armature Factor.
The number of conductors on an armature, counted or enumerated all
around its external periphery.

Armature, Hinged.
An armature pivoted to the end of one of the legs of an electro-magnet
so as to be free to swing and bring its other end down upon the other


Armature, Hole.
An armature whose core is perforated to secure cooling.

Synonym--perforated Armature.

Armature, Intensity.
An armature wound for high electro-motive force. A term little used at
the present time.

Armature Interference.
A limit to the ampere turns permissible on a given armature is found in
the increase of cross magnetizing effect, q. v., the increased lead
necessitated, and the growth of the demagnetizing power. All such
perturbing effects are sometimes expressed as armature interference.


Armature, Load of.
The circumflux, q. v., of the armature, or the ampere turns of the same.
The maximum load which can be carried by an armature without sparking is
directly proportional to the radial depth of core and to the length of
the gap, and inversely proportional to the breadth of the polar span.

Armature, Multipolar.
An armature in which a number of poles greater than two is determined by
the field. A multipolar field is employed for its production.

Armature, Neutral.
An armature of a magnet or telegraph relay which is not polarized or

Synonym--Non-polarized Armature--Neutral Relay Armature.

Armature of Influence Machine.
Pieces of paper pasted on the stationary plate of an electric machine of
the Holtz type.

Armature of Leyden Jar or Static Condenser.
The inner and outer tin-foil coatings of a Leyden jar or other

Armature, Open Coil.
An armature of a dynamo or motor on which the coils are not joined in
one closed circuit, but have their ends or some of them separated, and
connected each to its own commutator bar or each set to their own bar.



Armature, Pivoted.
An armature for an electro-magnet mounted on a pivot, which is at right
angles to the yoke or parallel with the legs of the magnet, so as to be
free to rotate. When the magnet is excited the armature is drawn into
line or approximately so with its base or yoke. The system is used in
some telegraph apparatus.

Armature Pockets.
Spaces or recesses in armatures provided for the reception of the coils.

Armature, Polarized.
An armature made of steel or having a steel core to which permanent
magnetism has been imparted. Such are used in some forms of magneto
current generators, and in telegraphic instruments. (See Relay,

Armature, Pole.
An armature having coils wound on separate poles projecting radially all
around the periphery of its central hub or disc, or projecting
internally from a ring-like frame, their ends facing the field magnet.

Synonym--Radial Armature.

Armature, Quantity.
An armature of a dynamo or motor wound for current of large quantity.
The term is now but little used.

When an armature is running in an active dynamo a series of
reactions is established, the more important of which are:
I. A tendency to cross-magnetize the armature.
II. A tendency to spark at the brushes.
III. A tendency for the armature current to demagnetize on account of
the lead which has to be given to the brushes.
IV. Variations in the neutral points as more or less current is taken
from the machine.
V. Heating of armature, both core and conductors, and of pole pieces,
which heating is due to Foucault currents.

Armature, Revolving, Page's.
An early form of motor. The field is produced by a permanent magnet.
Above its poles is a soft iron armature wound with a coil of insulated
wire. A two-part commutator with contact springs conveys the current to
the coil. The whole is so arranged that the polarity of the armature, as
induced by the coil, through which a current is passed, is reversed as
its ends sweep by the poles of the magnet. Then it is repelled from the
poles and swings through 180° to have its polarity reversed and to go
through the next 180°, and so on. Thus it rotates at a very high rate of

In the cut showing the elevation A, B, is the armature;  f, g, the
springs or brushes; h, the commutator with its sections o, i. In the
section of the commutator W, W, designate the springs or brushes, A, the
vertical spindle carrying the armature and commutator, and S, S, the
commutator sections.



W, W, Brushes; A, Spindle; S, S, Armature Segments.

Armature, Ring.
An armature whose core is in the shape of a ring, as the Gramme Ring
Armature. (See Figs. 23 & 27.)


Armature, Rolling.
(a) An armature for a permanent horseshoe magnet consisting of a
straight cylinder of soft iron on which a heavy wheel is mounted. When
the legs of the magnet are inclined downward and the bar is laid across
them it rolls down to the poles, across their ends, and back up the
under side. It is merely a magnetic toy or illustrative experiment.

Synonym--Wheel Armature.

(b) Another form consists of little bars of iron with brass discs
attached to the ends. On placing two of these together and bringing the
poles of a magnet near them, as shown, they become magnetized with like
polarity by induction and repel each other, rolling away in opposite



Armature, Shuttle.
The original Siemens' armature, now discarded. The core was long and
narrow, and its cross section was nearly of the section of an H. The
grooves were wound full of wire, so that the whole formed almost a
perfect cylinder, long and narrow comparatively. (See Winding Shuttle.)

Synonym--Siemens' Old Armature--Girder Armature--H Armature.


Armature, Spherical.
An armature of a dynamo which is wound on a spherical core, so as to be
almost a sphere. It is employed in the Thomson-Houston dynamo, being
enclosed in a cavity nearly fitting it, formed by the pole pieces.

Armature, Stranded Conductor.
A substitute for bar-armatures in which stranded copper wire conductors
are substituted for the solid bar conductors, to avoid Foucault
currents. (See Armature, Bar.)


Armature, Unipolar.
An armature of a unipolar dynamo. (See Dynamo Unipolar.)

Armor of Cable.
The metal covering, often of heavy wire, surrounding a telegraph or
electric cable subjected to severe usage, as in submarine cables.

Synonym--Armature of Cable.

Arm, Rocker.
An arm extending from a rocker of a dynamo or motor, to which arm one of
the brushes is attached. (See Rocker.) Ordinarily there are two arms,
one for each brush.

Articulate Speech.
Speech involving the sounds of words. It is a definition which has
acquired importance in the Bell telephone litigations, one contention,
concerning the Bell telephone patent, holding that the patentee did not
intend his telephone to transmit articulations, but only sound and

Astatic. adj.
Having no magnetic directive tendency due to the earth's magnetism.
Examples are given under Astatic Needle; Circuit, Astatic; and
Galvanometer Astatic.



Astatic Needle.
A combination of two magnetic needles so adjusted as to
have as slight directive tendency as possible. Such a pair of needles
when poised or suspended will hardly tend to turn more to one point of
the compass than another. The combination is generally made up of two
needles arranged one above the other, with their poles in opposite
directions. This combination is usually called Nobili's pair. If of
equal strength and with parallel magnetic axes of equal length they
would be astatic. In practice this is very rarely the case. A resultant
axis is generally to be found which may even be at right angles to the
long axis of the magnets, causing them to point east and west. Such a
compound needle requires very little force to turn it one way or the
other. If one of the needles is placed within a coil of insulated wire a
feeble current will act almost as strongly to deflect the system as if
the other was absent, and the deflection will only be resisted by the
slight directive tendency of the pair of needles. This is the basis of
construction of the astatic galvanometer. Sometimes coils wound in
opposite directions and connected in series, or one following the other,
surround both needles, thus producing a still greater effect of

Other astatic needles are shown in the cuts below. [Figures 33 to 35.]



A line continuously approached by a curve, but which the curve, owing to
its construction or nature of curvature, can never touch, be tangent to,
or intersect.

(a) A term applied to the atmospheric pressure as a practical unit of
pressure equal to 15 lbs. to the square inch as generally taken. It is
really about 14.7 lbs. per square inch, or 1,033 grams per square

(b) Air, q. v.

Atmosphere Residual.
The atmosphere left in a vessel after exhaustion. The term may be
applied to any gas. In an incandescent lamp after flashing the residual
atmosphere consists of hydro-carbons.

Atmospheric Electricity.
The electricity of the atmosphere, rarely absent, but often changing in
amount and sign. Benjamin Franklin, in a memoir published in 1749,
indicated the method of drawing electricity from the clouds by pointed
conductors. In June, 1752, he flew a kite and by its moistened cord drew
an electric spark from the clouds, confirming his hypothesis that
lightning was identical with the disruptive discharge of electricity. To
observe electricity in fine weather a gold-leaf or other electroscope
may be connected to the end of a long pointed insulated conductor. The
electricity during thunderstorms can be shown by a similar arrangement,
or burning alcohol or tinder gives an ascending current of warm air that
acts as a conductor. Quite elaborate apparatus for observing and
recording it have been devised. Atmospheric electricity is usually
positive, but occasionally negative. When the sky is cloudless it is
always positive, increasing with the elevation and isolation of the
place. In houses, streets, and under trees no positive electricity can
be found. In the Isle of Arran, Scotland, a rise of 24 to 48 volts per
foot of increase in elevation was found by Sir William Thomson. At
sunrise the electrification of the air is feeble, it increases towards
noon and decreases again to reach a second maximum a few hours after
sunset. It increases with the barometric pressure generally. In cloudy
weather it is sometimes negative and the sign often changes several
times in the same day. In a thunderstorm the changes in sign and
potential are very rapid. The cause of atmospheric electricity is far
from clear. Tait attributes it to a contact effect between air and water
vapor, Solmeke to friction of water vesicles against ice particles in
the upper atmosphere, he first showing that the two may coexist. The
cause of the enormous increase of potential producing lightning is
attributed to the decreased capacity due to the change of water from
cloud vesicles to drops, thus diminishing the electrostatic capacity of
the water in question. (See Lightning.)


The ultimate particle or division of an elementary substance; the
smallest part that can exist in combination, and one which cannot exist
alone. An elementary substance is composed of molecules just as truly as
a compound one, but the atoms in the molecule of an elementary substance
are all precisely alike. Hence atoms are the units of chemistry, they
have to do with combinations, but the physical unit, the smallest
particle of matter that can have an independent existence, is the
molecule. The two are often confounded, especially by writers of a few
years ago, so that by "atom" the molecule is often meant. There is
nothing to be said of their size or mass. All such calculations refer to
the molecule, q. v., often spoken of and called the atom.

[Transcriber's note: Yet to be discovered: electron--1897 (5 years),
proton--1920 (28 years), neutron--1932 (30 years), quark--1961 (69 years).]

Atomic Attraction.
The attraction of atoms for each other, in virtue of which they combine
into molecules; chemical affinity, q. v., treats principally of this,
although molecular attraction also plays a part in it.

Atomic Heat.
The product of the atomic weight of a substance by its specific heat.
This product is approximately the same, 6.4; this approximation is so
close that it is of use in determining the valency and atomic weights of
substances. The atomic weight of a substance therefore represents the
approximate number of gram-calories required to raise one gram-atom, q.
v., of such substance through 1° C. (1.8° F.)

The quantivalence or valency of the atoms; the number of combination
bonds, or bonds of affinity, possessed by the atoms of any substance.
Thus two atoms of hydrogen combine with one atom of oxygen, and three of
oxygen with one of sulphur, forming saturated compounds. Therefore,
taking hydrogen as of single atomicity or a monad, oxygen is of double
atomicity or a dyad, and sulphur is of six-fold atomicity, or a hexad.
The elements are thus classified into seven orders of atomicities, thus:

  1, Monads or Univalent elements,   Hydrogen, etc.
 2, Dyads or Bivalent        "      Oxygen, etc.
 3, Triads or Trivalent      "      Nitrogen, etc.
 4, Tetrads or Quadrivalent  "      Lead, etc.
 5, Pentads or Quinquivalent "      Phosphorous, etc.
 6, Hexads or Sexivalent     "      Chromium, etc.
 7, Heptads or Septivalent   "      Chromium, etc.

The same element often possesses several atomicities. Barium is
generally a dyad, sometimes a tetrad; nitrogen acts as a monad, dyad,
triad, tetrad and pentad. The familiar electrolysis of water, giving two
volumes of hydrogen to one of oxygen, is one of the illustrations of the
theory indicating that two atoms of hydrogen are combined with one of


Atomic Weight.
The number expressing the relative weight of the atom of any substance,
that of hydrogen being generally taken as unity. This is the universal
system, although any other element might be taken as the basis of the
system. The whole theory of atomic weights is based on the
indivisibility of the atom and on the theory of atomicity, q. v. (See

[Transcriber's note: The standard is now the isotope carbon-12 as
exactly 12.]

The tendency to approach and adhere or cohere, shown by all forms of
matter. It includes gravitation, cohesion, adhesion, chemical affinity
and other forms, and is opposed by repulsion, and is sometimes overcome
by it, although it may be assumed to be always present. See the
different kinds of attractions under their titles: Atomic Attraction,
Electro-magnetic Attraction and Repulsion, Electro Static Attraction and
Repulsion, Electro-dynamic Attraction and Repulsion; Magnetic Attraction
and Repulsion; Molar Attraction.

An apparatus for obtaining a balance of induction from two coils acting
upon a third. The third is placed between the other two and is free to
move towards either. A scale is provided to show the extent of its
movement. A varying or interrupted current being passed through the two
outer coils, the preponderating current will produce the most induction
if the central coil is equidistant. It can always be moved to such a
point that there will be no inductive effect, one counteracting the
other. Thus its position measures the relative induction. A telephone is
in circuit with the intermediate coil and is used to determine when its
position is such that no current is induced in it. It is sometimes used
as a direct test of hearing. (See Hughes' Induction Balance.)


Aura, Electrical.
The blast of air produced at highly electrified points.

A luminous display seen in the northern heavens in the northern
hemisphere, where it is the Aurora Borealis, and seen in the southern
heavens in the southern hemisphere, where it is called Aurora Australis,
or indifferently for either, the Aurora Polaris. It takes the form of
pale luminous bands, rays and curtains varying in color. Near the poles
they are very numerous. A French commission observed 150 auroras in 200
days. Their height is variously estimated at from 90 to 460 miles; they
are most frequent at the equinoxes and least so at the solstices. There
is a secular variation also, they attain a maximum of occurrence every
11 years together with sun spots, with a minimum 5 or 6 years after the
maximum. There is also a period of 60 years, coincident with
disturbances in the earth's magnetism. Various attempts have been made
to account for them. They have a constant direction of arc with
reference to the magnetic meridian (q. v.) and act upon the magnetic
needle; in high latitudes they affect telegraph circuits violently.
There is a strong probability that they represent electric currents or
discharges. De la Rive considers them due to electric discharges between
the earth and atmosphere, which electricities are separated by the
action of the sun in equatorial regions. According to Balfour Stewart,
auroras and earth currents.(q. v.) may be regarded as secondary currents
due to small but rapid changes in the earth's magnetism. The subject is
very obscure. Stewart treats the earth as representing the magnetic core
of an induction coil, the lower air is the dielectric, and the upper
rarefied and therefore conducting atmosphere is the secondary coil. This
makes the aurora a phenomenon of induced currents. Then the sun may be
regarded as the instigator of the primary changes in the earth's lines
of force representing the primary of an induction coil.

[Transcriber's note: Solar wind, streams of electrons and protons,
interacting with the earth's magnetic field causes aurora. Neither
electrons (1897) nor protons (1920) were known in 1892. The Soviet
satellite Luna first measured the solar wind in 1959. Even today
increased understanding of solar and auroral phenomenon continues.]


Austral Pole.
The north pole of the magnet is thus called sometimes in France; the
austral pole of a magnet is the one which points towards the north polar
regions As unlike magnetic poles attract each other, it is but rational
to call the north-seeking pole of the magnet the south or Austral Pole.
In the same nomenclature the south pole of a magnet, or the
south-seeking pole, is called the Boreal Pole.

A. W. G.
Abbreviation for American Wire Gauge, q. v.

Axis, Electric.
The electric axis of a pyroelectric crystal, such as a tourmaline
crystal; the line connecting the points of greatest pyroelectric

Axis of Abscissa.
In a system of rectilinear, or right angle co-ordinates, the horizontal
axis. (See Co-ordinates.)

Synonym--Axis of X.

Axis of Ordinates.
In a system of rectilinear right angle co-ordinates, the vertical axis.
(See Co-ordinates.)

Synonym--Axis of Y.

The angle between the plane of the meridian and the plane of an azimuth
circle, q. v.

Azimuth Circle.
A great circle, whose plane passes through the zenith or point of the
heavens directly overhead; any great circle in whose plane the vertical
at the point of observation is included.

Each celestial body has or determines an azimuth circle.


(a) Abbreviation for Baumé, a hydrometer scale. (See Baumé.) Thus 10º B.
means "ten degrees Baumé."

(b) Symbol for the coefficient of induced magnetization, or the number
of lines per square centimeter induced in a magnetic circuit or in any
specified part of it.

B. A.
Abbreviation for British Association. It is prefixed to standards fixed
by the committee of the British Association for the Advancement of
Science. Thus the B. A. ohm means the British Association ohm, a measure
of resistance which is equal to the resistance of a column of mercury
104.9 centimeters long and one square millimeter area of cross-section.
(See Ohm.)

Back Induction.
A demagnetizing force produced in a dynamo armature when a lead is given
the brushes. The windings by such setting of the brushes are virtually
divided into two sets, one a direct magnetizing set, the other a cross
magnetizing set. The latter have a component due to the obliqueness of
the neutral line, which component is demagnetizing in its action.

Back Shock or Stroke of Lightning.
A lightning stroke received after the main discharge of the lightning,
and caused by a charge induced in neighboring surfaces by the main
discharge. The discharge affects the evenness of distribution of
surrounding surfaces so that a species of secondary discharge is
required to make even the distribution, or to supply charge where needed
to bind an opposite one. The effects are much lese severe as a rule than
those of the main charge, although the back stroke has caused death. The
back stroke is sometimes felt a considerable distance from the place of
the original lightning stroke.

Synonym--Return Stroke.

Back Stroke.
(a) In telegraphy the return stroke of the lever in a telegraph sounder,
striking the end of the regulating screw with a sound distinct from that
which it produces on the forward stroke as it approaches the magnet
poles. It is an important factor in receiving by ear or sound reading.

(b) See Back Shock or Stroke of Lightning.

(a) Wheatstone's Bridge, q. v., is sometimes termed the Electric

(b) A suspension or torsion balance is one which includes a filament or
pair of filaments to whose lower end or ends are attached a horizontal
indicator often called a needle, or a magnetic needle. (See Torsion

(c) See Induction Balance, Hughes'.

(d) For Thermic Balance, see Bolometer.

(e) See Balance, Ampere.


Balance, Ampere.
A class of electrical measuring instruments due to Sir William Thomson
may be grouped under this head.

The instrument is a true balance or scales such as used for weighing. It
is supported by a torsional wire support in place of knife edges. At
each end it carries a circle of wire through which the current to be
tested is passed. The torsional wire support enables the current to be
carried to these wire rings. Above and below each of these rings are two
similar rings, also connected so as to receive the current. They are so
connected that the current shall go through them in opposite senses.
When a current passes, therefore, one of these rings repels and one
attracts the balanced ring.

The extent of this action measures the intensity of the current. A
sliding weight moving along a graduated scale on the balance is used to
bring the balance beam into equilibrium when the current is passing. The
degree of displacement of this weight gives the strength of the current
in amperes.

These balances are made for different currents. Thus there is a
centi-ampere balance, deka-ampere balance and others, as well as an
ampere balance.

A gum used as an insulating material. It is the inspissated juice of a
sapotaceous tree, the bullet tree, Mimusops globosa, of tropical
America, from the Antilles to Guiana. It is intermediate in character
between caoutchouc and gutta percha. It is superior to gutta percha in
some respects, being very slightly acted on by light.


B. & S.. W. G.
Abbreviation for Brown & Sharpe Wire Gauge; the regular American Wire
Gauge. (See Wire Gauge, American.)

An absolute or fundamental unit of pressure, equal to one dyne per
square centimeter.

An apparatus for measuring the pressure exerted by the atmosphere. It
consists, in the mercurial form, of a glass tube, over 31 inches long,
closed at one end, filled with mercury and inverted, with its open end
immersed in a cistern of mercury. The column falls to a height
proportional to the pressure of the atmosphere from 30 to 31 inches at
the sea level. The "standard barometer" is a height of the mercury or of
the "barometric column" of 30 inches or 760 centimeters, measured from
the surface of the mercury in the cistern.

The column of mercury is termed the barometric column. Above it in the
tube is the Torricellian vacuum.

[Transcriber's note: More accurately, 29.92 inches of mercury or 14.696

Bars of Commutators.
The metal segments of a commutator of a dynamo or motor. They are made
of bars of copper, brass or bronze insulated from one another. (See

Synonyms--Segments, Commutator Segments, Commutator Bars.


(a) In electro-plating the solution used for depositing metal as
contained in a vat or tank; as a silver, copper, or nickel bath used for
plating articles with silver, copper, or nickel respectively.

(b) In electro-therapeutics a bath with suitable arrangements,
electrodes and connections for treating patients with electricity. It is
termed an electric bath or electro-therapeutic bath.

Bath, Bipolar Electric.
In electro-therapeutics a bath in which the electrodes are both immersed
in the water. The patient placed between them receives part of the
discharge. The electrodes are large copper plates, termed shovel

Bath, Electric Shower.
An electro-medical shower bath. The patient is placed on a metallic
stove or support connected to one of the electric terminals. Water
slightly alkaline is showered upon him. The other electrode is in
connection with the water. The rain of drops and streamlets is the
conductor of the current or discharge.

Bath, Multipolar Electric.
An electro-medical bath with a number of electrodes instead of two.

Bath, Stripping.
In electro-plating a solution used for dissolving and thus removing the
plating from any object. The stripping bath is of the same general type
as the plating bath for the same metal as the one to be dissolved. The
object to be "stripped" is made the anode of a plating circuit, and as
the current acts the old plating is attacked and dissolves, leaving the
body of the article bare. It is simply the operation of plating
reversed. The same term is applied to baths acting by simple solution.
Stripping baths are described under the different metals as Silver Bath,
Stripping--Gold Bath, Stripping.

Bath, Unipolar Electric.
An electro-medical bath, in which only one electrode connects with the
water of the bath. The second electrode is supported above the bath. The
patient touches this while in the water whenever electric action is




A strip of wood grooved longitudinally for holding wires in wiring
apartments for electric light or power. In use they are fastened to the
wall, grooves inward, or else grooves outward, with the wires lying in
the grooves and covered with the covering strip. For two wire work each
batten contains two grooves; for the three wire system it contains three


A combination of parts or elements for the production of electrical
action. The term is principally applied to voltaic batteries, but there
are also magnetic batteries, batteries of Leyden jars, and other
combinations, described in their places, which come under this category.

[Transcriber's note: A group of similar items such as questions,
machines, parts, guns, or electric cells.]

Battery, Acetic Acid.
A battery whose active solution or excitant is acetic acid or vinegar.
This acid has been used by Pulvermacher in his medical battery, as being
a substance found in every household in the form of vinegar. It is now
but little used.

Battery, Alum.
A battery using as excitant a solution of alum. This battery has had
some application for electric clocks, but only to a limited extent.


Battery, Aluminum.
A battery in which aluminum is the negative plate and aluminum sulphate
the excitant. It is mounted like the gravity battery. Its electro-motive
force is 0.2 volt.


Battery, Bagration.
A battery with zinc and carbon electrodes immersed in earth sprinkled
with sal ammoniac (ammonium chloride). The copper is preferably first
immersed in sal ammoniac solution and dried, until a green layer is
formed on its surface.

The battery is highly praised for its constancy by De la Rive, but may
be regarded as obsolete.

Battery, Balloon.
A form of gravity battery into whose centre a globular flask, B, is
inverted, which is filled before inversion with copper sulphate, of
which 2 lbs. are used, and water, so as to remain full. This acts as a
reservoir of copper sulphate, which it constantly supplies. The glass
jar is closed with a perforated wooden cover.

Battery, Banked.
(a) A battery arranged to feed a number of separate circuits.

(b) A battery connected in parallel or in multiple arc.

Battery, Bichromate.
A battery with amalgamated zinc and carbon plates, with an exciting
fluid composed of sulphuric acid, water, and potassium bichromate. For
formula of such solutions see Electropoion Fluid--Kookogey's
Solution--Poggendorff's Solution--Trouvé's Solution--Delaurier's
Solution, and others. (See Index.)

Battery, Bunsen.
A two fluid porous cell battery. The negative plate is carbon, the
positive plate, amalgamated zinc. The depolarizer is nitric acid or
electropoion fluid, q.v., in which the carbon is immersed. The last
named depolarizer or some equivalent chromic acid depolarizing mixture
is now universally used.  The excitant is a dilute solution of sulphuric
acid. Originally the carbon was made cylindrical in shape and surrounded
the porous cups, in which the zinc was placed. This disposition is now
generally reversed. The electro-motive force is 1.9 volts. The
depolarizing solution is placed in the compartment with the carbon. The
excitant surrounds the zinc.



Battery, Cadmium.
A battery in which cadmium is the negative plate, sulphate of cadmium
solution the excitant and depolarizer, and zinc the positive plate.
Electro-motive force, .31 volt or about one third of a Daniell cell. It
is mounted like a gravity battery.

Battery, Callan.
A modification of Grove's battery. Platinized lead is used for the
negative plate, and as a depolarizer a mixture of 4 parts concentrated
sulphuric acid, 2 parts of nitric acid, and 2 parts of a saturated
solution of potassium nitrate. (See Battery, Grove's.)

Battery, Camacho's.
A battery with carbon negative and amalgamated zinc positive electrodes.
The carbon is contained in a porous cup, packed with loose carbon.
Electropoion or other fluid of that type serves as excitant and
depolarizer, and is delivered as shown from cell to cell by syphons.


Battery, Carré's.
A Daniell battery for whose porous cup a vessel or species of sack made
of parchment paper is substituted. The battery has been used for
electric light, and has been run for 200 successive hours, by replacing
every 24 hours part of the zinc sulphate solution by water.


Battery, Cautery.
A battery used for heating a platinum wire or other conductor used for
cauterization in electro-therapeutics. The term is descriptive, not

Battery, Chloric Acid.
A battery of the Bunsen type in which an acidulated solution of
potassium chlorate is used as depolarizer.

Battery, Chloride of Lime.
A battery in which bleaching powder is the excitant. The zinc electrode
is immersed in a strong solution of salt, the carbon in a porous vessel
is surrounded with fragments of carbon and is packed with chloride of
lime (bleaching powder). There is no action on open circuit. It has to
be hermetically sealed on account of the odor. Its electro-motive force
is--initial, 1.65 volts; regular, 1.5 volts.

Synonym--Niaudet's Battery.

Battery, Chromic Acid.
Properly a battery in which chromic acid is used as a depolarizer. It
includes the bichromate battery. (See Battery, Bichromate.)

Battery, Closed Circuit.
A battery adapted by its construction to maintain a current on a closed
circuit for a long time without sensible polarization. The term is
merely one of degree, for any battery becomes exhausted sooner or later.
As examples the Grove, Bunsen or Daniell batteries may be cited.



Battery, Column.
The original Volta's pile. It consists of a series of compound circular
plates, the upper or lower half, A, copper; the other, Z, of zinc.
Between each pair of plates some flannel or cloth, u, u, is laid, which
is saturated with dilute acid. As shown in the cut, the parts are laid
up in two piles, connected at the top with a bar, c, c, and with vessels
of acidulated water, b, b, as electrodes. The great point in setting it
up is to be sure that no acid runs from one disc of flannel to the next
over the outside of the plates, as this would create a short circuit.
The plates are best compound, being made up of a zinc and a copper plate
soldered together. They may, however, be separate, and merely laid one
on the other. In such case great care must be taken to admit no acid
between them.

Volta's pile is no longer used, except occasionally. Trouvé's blotting
paper battery (see Battery, Trouvé's) is a relic of it, and the same is
to be said for Zamboni's dry pile.

It rapidly polarizes, the flannel retains but little acid, so that it is
soon spent, and it is very troublesome to set up. Great care must be
taken to have the cloth discs thoroughly saturated, and wrung out to
avoid short circuiting by squeezing out of the acid.

Battery, D'Arsonval's.
A battery of the Bunsen type, differing therefrom in the solutions. As
excitant in which the zinc electrode is immersed, the following solution
is used:

Water, 20 volumes;
Sulphuric Acid (purified by shaking with a little olive or similar oil),
1 volume;
hydrochloric acid, 1 volume.

As polarizer in which the carbon is immersed the following is used:

Nitric acid, 1 volume;
hydrochloric acid, 1 volume;
water acidulated with 1/20th sulphuric acid, 2 volumes.

Battery, de la Rue.
A battery with zinc positive and silver negative electrode; the
depolarizer is silver chloride; the excitant common salt or ammonium
chloride. The cut shows one of its forms of construction.

The right hand portion of the cut, Fig. 42, shows the zinc perforated at
C for the connection from the next silver plate. The next to it is the
negative electrode of silver around which a mass of silver chloride is
cast in cylindrical form. A is a parchment paper cylinder with two holes
near its top, through which the silver wire of the negative electrode is
threaded, as shown in B. A solution of 23 parts ammonium chloride in
1,000 parts of water is the approved excitant. Its electro-motive force
is 1.03 volts.

The jars are closed with paraffin.



Battery, Dry.
(a) A form of open circuit battery in which the solutions by a mass of
zinc oxychloride, gypsum, or by a gelatinous mass such as gelatinous
silica, or glue jelly, are made practically solid. Numbers of such have
been patented, and have met with considerable success.

(b) Zamboni's dry pile, q. v., is sometimes termed a dry battery.

Battery, Element of.
A term applied sometimes to a single plate, sometimes to the pair of
plates, positive and negative, of the single couple.

Battery, Faradic.
A term applied, not very correctly however, to apparatus for producing
medical faradic currents. It may be an induction coil with battery, or a
magneto-generator worked by hand.

Battery, Ferric Chloride.
A battery of the Bunsen type, in which a solution of perchloride of iron
(ferric chloride) is used for the depolarizing agent. A little bromine
is added with advantage. The depolarizing agent recuperates on standing,
by oxidation from the oxygen of the air.

Battery, Fuller's.
A battery of the Bunsen type. The zinc plate is short and conical, and
rests in the porous jar into which some mercury is poured. An insulated
copper wire connects with the zinc. A plate of carbon is in the outer
jar. The solutions are used as in the Bunsen battery.

Synonym--Mercury Bichromate Battery.

Battery, Gas.
(a) A battery whose action depends on the oxidation of hydrogen as its
generating factor. It was invented by Grove. Plates of platinum are
immersed in cups of dilute acid, arranged as if they were plates of zinc
and carbon, in an ordinary battery. Each plate is surrounded by a glass
tube sealed at the top. The plates are filled with acid to the tops.
Through the top the connection is made. A current from another battery
is then passed through it, decomposing the water and surrounding the
upper part of one set of plates with an atmosphere of oxygen and of the
other with hydrogen. Considerable quantities of these gasses are also
occluded by the plates. On now connecting the terminals of the battery,
it gives a current in the reverse direction of that of the charging

This battery, which is experimental only, is interesting as being the
first of the storage batteries.

(b) Upward's Chlorine Battery and any battery of that type (see Battery,
Upward's,) is sometimes termed a gas battery.


Battery Gauge.
A pocket or portable galvanometer for use in testing batteries and

Battery, Gravity.
A battery of the Daniell type, in which the porous cup is suppressed and
the separation of the fluids is secured by their difference in specific
gravity. A great many forms have been devised, varying only in details.
The copper plate, which is sometimes disc shaped, but in any case of
inconsiderable height, rests at the bottom of the jar. Near the top the
zinc plate, also flat or of slight depth, is supported. As exciting
liquid a strong solution of copper sulphate lies at the bottom of the
jar. This is overlaid by a solution of zinc sulphate, or sodium
sulphate, which must be of considerably less specific gravity than that
of the copper sulphate solution. In charging the jar one-tenth of a
saturated solution of zinc sulphate mixed with water is sometimes used
as the upper fluid. This may be first added so as to half fill the jar.
The strong solution of copper sulphate may then be added with a syphon
or syringe underneath the other so as to raise it up. From time to time
copper sulphate in crystals are dropped into the jar. They sink to the
bottom and maintain the copper sulphate solution in a state of


If the battery is left on open circuit the liquids diffuse, and metallic
copper precipitates upon the zincs. This impairs its efficiency and
creates local action. As long as the battery is kept at work on closed
circuit work but little deposition, comparatively speaking, occurs.

From time to time, in any case, the zinc plates are removed and scraped,
so as to remove the copper which inevitably forms on their surface. Care
must be taken that the zinc sulphate solution, which is constantly
increasing in strength, does not get so strong as to become of as high
specific gravity as the copper sulphate solution. From time to time some
of the upper solution is therefore removed with a syphon or syringe and
replaced with water. An areometer is useful in running this battery.


Battery, Grenet.
A plunge battery with zinc positive and carbon negative electrodes.
Electropoion or other chromic acid or bichromate solution is used as
depolarizer and excitant. The zinc plate alone is plunged into and
withdrawn from the solution.



Battery, Grove's.
A two fluid galvanic battery. A porous cup has within it a riband of
platinum, which is the negative plate; amalgamated zinc in the outer jar
is the positive plate. Dilute sulphuric acid (10 per cent. solution) is
placed in the outer jar, and strong nitric acid (40° B.) as a
depolarizer in the porous cups. Its E. M. F. is 1.96 volts.

It is objectionable, as it gives off corrosive nitrous fumes. These are
produced by the oxidation of the nascent hydrogen by the nitric acid, by
the following reaction:

3 H + H N O3 = 2 H2 O + N O. There are other reactions, one of which
results in the formation of ammonia by the reduction of the nitric acid
radical by the hydrogen. Ammonium can be detected in the spent liquids.


Battery, Hydrochloric Acid.
A battery in which hydrochloric acid is used as the excitant. Many
attempts have been made to use this acid in batteries, but the volatile
nature of the acid causes the production of so much odor with corrosive
fumes that it has never come into use.

Battery, Lead Chloride.
A battery of the lead sulphate type in which lead chloride is the
depolarizer. It has had no extended use.

Battery, Lead Sulphate.
A battery similar to Marié Davy's battery or the gravity battery, but
using lead sulphate as depolarizer and excitant. Lead, copper or tin is
the material of the negative plate. Becquerel used the lead sulphate as
a solid cylindrical mass surrounding a lead rod 1/5 to 1/4 inch in
diameter. One part of common salt may be mixed with 5 parts of the lead
sulphate. The electro-motive force is about 0.5 volt. The resistance is
very high.

Battery, Leclanché.
An open circuit battery with porous cup. In the outer jar is a zinc rod;
a carbon plate is placed in the porous cup. The latter is packed with a
mixture of clean powdered manganese binoxide as depolarizer, and
graphite in equal volumes. A strong solution of ammonium chloride (sal
ammoniac) is placed in the outer jar. It is only used on open circuit
work. Its electromotive force is 1.48 volts, when not polarized.

The reaction is supposed to be about the following:

2 N H4 Cl + 2 Mn O2 + Zn = Zn Cl2 + 2 N H3 + H2 0 + M2 O3

The battery rapidly weakens on open circuit, but quickly recuperates.
There is another form of this battery, termed the agglomerate battery.
(See Battery, Leclanché Agglomerate.)


Battery, Leclanché Agglomerate.
A form of the Leclanché in which the porous jar is suppressed. Cakes
made of a mixture of carbon, 52 parts; manganese binoxide, 40 parts; gum
lac, 5 parts; potassium bisulphate, 3 parts, compressed at 300
atmospheres, at a temperature of 100° C. (212° F.), are fastened by
India rubber bands or otherwise against the carbon plate. These
constitute the depolarizer. Various shapes are given the carbon and
depolarizing agglomerates.

Battery, Local.
A battery supplying a local circuit (see Circuit. Local). The current is
governed by the relay situated on the main line and operated by its

Battery, Main.
The battery used in operating the main line. It is usually applied to
telegraphy. Its function is then to supply current for working relays,
which in turn actuate the local circuits.

Main and local circuits and batteries are also used in the automatic
block system of railroad signalling.


Battery, Marié Davy's.
A two fluid porous cup battery with carbon negative plate, zinc positive
plate, and mercury sulphate, a nearly insoluble salt, as depolarizer and
excitant. Mercurous or mercuric sulphates have been used in it. Its
electromotive force is 1.5 volts. The local action and waste, owing to
the slight solubility of the mercury compounds, is very slight. If used
on close circuit it becomes polarized. It is also subject under extreme
circumstances to reversal of polarity, zinc becoming deposited upon the
carbon, and there forming a positive electrode.

In using the cells in series the level of liquid in all must be the
same, otherwise the cell in which it is lowest will become polarized and

Modifications of this battery on the lines of the gravity battery have
been constructed.

Synonym--Sulphate of Mercury Battery.

Battery, Maynooth's.
A battery of the Bunsen type, with cast iron negative plate. The iron
takes the passive form and is not attacked.

Battery, Medical.
A term applied very indiscriminately to medical current generators, and
to medical induction coils, or to any source of electricity, static or
current, for medical application.


Battery, Meidinger's.
A variety of Daniell cell of the gravity type. The plates are
cylindrical. The zinc plate lies against the upper walls of the vessel.
The copper plate of smaller diameter rests on the bottom. A large tube,
with an aperture in its bottom, is supported in the centre and is
charged with copper sulphate crystals. The cup is filled with a dilute
solution of Epsom salts (magnesium sulphate) or with dilute sulphuric

Battery Mud.
A deposit of mud-like character which forms in gravity batteries and
which consists of metallic copper precipitated by the zinc. It indicates
wasteful action.

Battery, Multiple-connected.
A battery connected in parallel, all the positive plates being connected
to one electrode, and all the negative to another.

Battery, Nitric Acid.
A battery in which nitric acid is used as the excitant. Owing to its
cost and volatility this acid has been but little used in batteries,
other than as a depolarizer. In Grove's battery (see Battery, Grove's)
it has been thus used.

Battery of Dynamos.
A number of dynamos may be arranged to supply the same circuit. They are
then sometimes termed as above, a Dynamo Battery. They may be arranged
in series or in parallel or otherwise combined.

Battery of Leyden Jars.
To produce the quantity effect of a single large Leyden jar with a
number of small ones they are often connected in parallel and termed a
battery. In such case the inner coatings are all connected by regular
bar conductors, and the outside coatings are also all in connection.
They are conveniently placed in a box or deep tray whose inner surface
is lined with tinfoil, with an outside connection for grounding, etc.
The cascade, q. v., arrangement is not so generally termed a battery.

Battery, Open Circuit.
A battery adapted for use in open circuit work. Its main requirement is
that it shall not run down, or exhaust itself when left on open circuit.
The Leclanché battery is very extensively used for this work. Its action
is typical of that of most open circuit batteries. It is without any
action on open circuit. It is very quickly exhausted on closed circuit,
but recuperates or depolarizes quite soon when on open circuit. It is
always in condition for a momentary connection, but useless for steady

Battery, Oxide of Copper.
A battery with zinc positive and iron negative electrodes. The excitant
is a 30 or 40 per cent. solution of sodium or potassium hydrate (caustic
soda or caustic potash). The depolarizer is copper oxide. In action the
copper is gradually reduced to the metallic state. The iron element is
often the containing vessel. The battery is practically inactive on open

Its electro-motive force varies from .75 to .90 volt. To prevent the
formation of sodium or potassium carbonate the cell should be closed, or
else the liquid should be covered with mineral oil.

Synonyms--Lalande & Chaperon Battery--Lalande-Edison Battery.


Battery, Peroxide of Lead.
A battery in which peroxide of lead (lead binoxide) is the depolarizer.
It is a sort of predecessor of the present secondary battery.

Battery, Platinized Carbon.
A modification of Smee's battery, in which platinized carbon is used for
the negative plates. Before polarization the E. M. F. is equal to that
of Smee's battery. Polarization reduces its electro-motive force

Battery, Plunge.
A battery whose plates are mounted so as to be immersed in the battery
cups or cells, when the battery is to be used, and withdrawn and
supported out of the cups when not in use. The object is to prevent
wasting of the plates by standing in the solution. It is a construction
generally used with sulphuric acid--chromic acid solution and
amalgamated zinc and carbon plates.

Battery, Pneumatic.
A battery arranged to have air blown through the solution to assist
diffusion and depolarization. It is a construction applied to chromic
acid or bichromate batteries.

Battery, Primary.
A battery in which the current is supplied by the solution of one of the
plates by the solution. The term distinguishes it from a secondary or
storage battery.

Battery, Pulvermacher's Electro-Medical.
In this battery, the electrodes were zinc and copper wires wound upon
small pieces of wood. Dilute vinegar was used as the excitant, because
it could be found in every household. Formerly the battery had great
success. It is now little used.

Battery, Sal Ammoniac.
Batteries in which a solution of ammonium chloride is the excitant; they
are very extensively used on open circuit work. (See Battery,

The crystals formed in these batteries have been analyzed and found to
consist of ammonium zinc chloride, 3 Zn Cl2, 8 N H3, 4 H20.

Battery, Salt, or Sea Salt.
Batteries in which a solution of sodium chloride or common salt is the
excitant, have been largely used, especially for telegraphic purposes.
The Swiss telegraphs use a carbon-zinc combination with salt and water
as the excitant. The batteries are sometimes mounted as plunge
batteries. They are exhausted by short circuiting after some hours, but
recuperate on standing. The zinc is not amalgamated.


Battery, Sand.
A battery whose cells are charged with sand saturated with dilute acid.
It prevents spilling of acid. It is now practically obsolete.


Battery, Secondary.
A voltaic battery whose positive and negative electrodes are formed or
deposited by a current from a separate source of electricity by
electrolysis. On disconnection the battery is ready to yield a current,
in the reverse direction of that of the charging current. The usual type
has lead plates on one of which lead binoxide and on the other of which
spongy lead is formed. The lead binoxide seems to be the negative
element, and it also acts as the depolarizer. The spongy lead is the
positive electrode. The solution is dilute sulphuric acid of specific
gravity 1.17. The action consists first in the oxidation of the spongy
lead. The hydrogen set free by the reaction, and which by electrolytic
transfer goes to the other plate, reduces the lead binoxide to
protoxide. The sulphuric acid then attacks the oxides and converts the
oxides into sulphates.

The charging process consists in sending a current in the reverse
direction through the battery. If there are several cells they are
arranged in series, so that each one receives the same intensity of
current. An electrolytic decomposition takes place, the lead sulphate on
one plate is reduced to metallic lead, and that on the other plate is
oxidized to lead binoxide. It is then ready for use.


The plates in a lead plate battery are of very large area per cell, and
are placed close together. Sometimes, as in Planté's battery, large flat
plates are laid together with a separating insulator between them, and
are then rolled into a spiral. Sometimes, the most usual arrangement,
the plates are in sets, the positive and negative ones alternating, and
each cell containing a number of plates.

To secure a good quantity of active material, the plates are sometimes
perforated, and the perforations are filled with oxide of lead. This
gives a good depth of material for the charging current to act on, and
avoids the necessity for a tedious "forming," q. v.

The electro-motive force of such a battery per cell is 2 volts. Its
resistance may only be one or two-hundredths of an ohm. An intense
current of many amperes can be supplied by it, but to avoid injuring the
cell a current far less than the maximum is taken from it.

To charge it, a slightly greater electro-motive force, the excess being
termed spurious voltage, is required.



Battery, Secondary, Plante's.
Plante's secondary battery is one of the earlier forms of storage
battery, but has had much success. Two lead plates, large in area and
close together but not touching, are "formed," by exposure to an
electrolyzing current of electricity in one direction, while they are
immersed in dilute sulphuric acid. This converts the surface of one
plate into binoxide. The cell is then allowed to discharge itself almost
completely, when the charging current is again turned on. This process
is repeated over and over again, until the surfaces of the plates are
considerably attacked, one plate, however, being maintained in a state
of oxidation. After a few days of this operation a period of rest is
allowed between the reversals, which sets up a local action on the
oxidized plate, between the metallic lead of the plate, and its coating
of binoxide. This causes the lead to be attacked, under the influence of
the local couple, and sulphate of lead is formed, which, ultimately, by
the charging current is converted into peroxide. These operations
produce an exceedingly good battery. The process described is termed

The plates separated by strips of insulating material are generally
wound into a double spiral.

Battery, Siemens' and Halske's.
A Daniell battery of peculiar shape. The copper, C, is at the bottom of
the glass jar, A. The inner jar, K, has the form of a bell, and supports
a mass of paper pulp, which is dampened with sulphuric acid. The zinc,
Z, rests on top of the mass of pulp. The battery is very durable, but of
high resistance.

Battery, Sir William Thomson's.
A form of Daniell battery, of the gravity type. The receptacles are
shallow wooden trays lined with lead. A thin plate of copper rests on
the bottom. The zinc plate is of gridiron shape, and rests on wooden
blocks which support it in a horizontal position above the copper. One
tray is placed on top of the other, the upper tray resting on the
corners of the zinc plate which rise above the level of the top of the
flat vessel. Thus connection is assured without wires or binding posts.
It is charged like a gravity battery. The density of the zinc sulphate
solution should be between 1.10 and 1.30. The circuit must be kept
closed to prevent deposition of metallic copper on the zinc. The entire
disposition of the battery is designed to reduce resistance.

Battery, Skrivanow.
A pocket battery of the De la Rue type, with a solution of 75 parts
caustic potash in 100 parts of water as the excitant. The silver
chloride is contained in a parchment paper receptacle. Its
electro-motive force is 1.45 to 1.5 volts.

Battery, Smee's.
A single fluid combination, with zinc positive plate, and a plate of
silver, coated with platinum black, for the negative plate. The finely
divided platinum affords a surface from which the hydrogen bubbles
instantly detach themselves, thus preventing polarization. The liquid is
a mixture of one part sulphuric acid to seven parts of water. For the
negative plate silver-plated copper, coated with platinum black, is
used. Electromotive force, .47 volt.




Battery, Spiral.
A battery whose plates of thin zinc and copper are wound into a spiral
so as to be very close, but not touching. Dilute sulphuric acid is the
excitant. It is now practically obsolete.

Synonyms--Calorimeter--Hare's Deflagrator.

Battery, Split.
A battery of a number of voltaic cells, connected in series, with their
central portion grounded or connected to earth. This gives the ends of
opposite potentials from the earth, and of difference therefrom equal to
the product of one-half of the number of cells employed, multiplied by
their individual voltage.

Battery Solutions, Chromic Acid.
A number of formulae have been proposed for these solutions. (See
Electropoion Fluid--Kookogey's Solution--Poggendorff's Solution--
Trouvé's Solution--Delaurier's Solution--Chutaux's Solution--Dronier's
Salt--Tissandier's Solution.)

Battery, Trough.
A battery whose elements are contained in a trough, which is divided by
cross-partitions so as to represent cups. A favorite wood for the trough
is teak, which is divided by glass or slate partitions. Marine glue or
other form of cement is used to make the joints tight. For porous cup
divisions plates of porous porcelain or pottery are placed across,
alternating with the impervious slate partitions.

Battery, Trouvé's Blotting Paper.
A battery of the Daniell type in which the solutions are retained by
blotting paper. A considerable thickness of blotting paper lies between
the two plates. The upper half of the thickness of the blotting paper is
saturated with a solution of zinc sulphate, on which the zinc plate

The lower half of the paper is saturated with copper sulphate solution,
and this rests upon the copper plate.



Battery, Tyer's.
A modification, as regards the positive element, of Smee's battery, q.
v. The bottom of the battery jar contains a quantity of mercury in which
pieces of zinc are thrown, and this constitutes the positive element.

A ball of zinc at the end of an insulated copper wire affords the
connection with the zinc and mercury. Its great advantage is that the
smallest scraps of zinc can be used in it, by being dropped into the
mercury. The negative plate is platinized silver; the exciting liquid,
dilute sulphuric acid.





Battery, Upward's.
A primary voltaic cell, the invention of A. Renée Upward. Referring to
the cuts, the positive plate. Z, is of cast zinc; it is immersed in
water, in a porous cup, B. Outside of the porous cup and contained in
the battery jar are two carbon plates, C, C, connected together. The
rest of the space between the porous cup and battery jar is packed with
crushed carbon, and the top is cemented. Chlorine gas is led by a pipe,
D, into the outer cell. It diffuses through the fine carbon, dissolves
in the water, and so finds its way to the zinc, which it attacks,
directly combining therewith, and forming zinc chloride (Zn + 2 Cl = Zn
Cl 2). Such of the chlorine as is not absorbed finds its way by an outlet
tube, E, to the next cell. Arrangements are provided for generating
chlorine gas as required. The high specific gravity of the gas is
utilized in regulating its distribution through the cells. The
electro-motive force of the cell is 2.1 volts. A cell 11.5 by 5.5 inches
and 12.5 inches deep has a resistance of 0.2 ohm.

An overflow pipe, F, with faucet, T, is supplied to withdraw the
solution of zinc chloride as it accumulates.


Battery, Varley's.
A Daniell battery of the Siemens' and Halske's type (see Battery,
Siemens' and Halske's), in which zinc oxide is substituted for the paper
pulp of the other battery. It has been very little used.

Battery, Volta's.
The original acid battery. It has a negative electrode of copper, a
positive electrode of zinc; the excitant is sulphuric acid diluted with
sixteen times its volume of water. It rapidly polarizes, and is very
little used.

Battery, Voltaic or Galvanic.
An apparatus for converting chemical energy directly into electric
energy. This is as broad a definition as can well be given. The general
conception of a battery includes the action of electrolysis, a solution
in the battery acting upon one of two conducting electrodes immersed in
such fluid, which dissolves one of them only, or one more than the
other. The best way to obtain a fundamental idea of a battery is to
start with the simplest. Dilute sulphuric acid dissolves neither pure
zinc nor copper. But it has a far stronger affinity for the first named
metal. If now we immerse in dilute acid two plates, one of pure zinc,
and one of copper, no action will be discernible. But if the plates are
brought in contact with each other a stream of bubbles of hydrogen gas
will escape from the surface of the copper and the zinc will dissolve.
By applying proper tests and deductions it will be found that the copper
and zinc are being constantly charged with opposite electricities, and
that these are constantly recombining. This recombination produces what
is known as an electric current.

To constitute a battery the zinc and copper plates must be connected
outside of the solution. This connection need not be immediate. Any
conductor which touches both plates will bring about the action, and the
current will pass through it.

The easiest way to picture the action of a battery is to accept the
doctrine of contact action. In the battery the molecules of water are
pulled apart. The hydrogen molecules go to the copper, the oxygen
molecules go to the zinc, each one, leaving its contact with the other,
comes off charged with opposite electricity. This charges the plates,
and the continuous supply of charge and its continuous discharge
establishes the current.

The accumulation of hydrogen acts to stop the action by polarization.
Its own affinity for oxygen acts against or in opposition to the
affinity of the zinc for the same element, and so cuts down the action.
A depolarizer of some kind is used in acid batteries for this reason. As
such depolarizer has only to act upon one plate, in most batteries it is
usual to surround such plate only, as far as it is possible, with the
depolarizer. The solution which dissolves the zinc is termed the
excitant or exciting solution.

To this concrete notion of a voltaic battery the different modifications
described here may be referred. Zinc, it will be seen, forms the almost
universally used dissolved plate; carbon or copper forms the most usual
undissolved plate; sulphuric acid in one form or another is the most
usual excitant.

The solution in a voltaic battery is electrolyzed (see Electrolysis).
Hence the solutions must be electrolytes. The sulphuric acid and other
ingredients play a secondary role as imparting to the battery fluids
this characteristic.

It is not necessary to have electrodes of different substances, the same
metal maybe used for both if they are immersed in different solutions
which act differentially upon them, or which act with more energy on one
than on the other. Such are only of theoretical interest.


Battery, Water.
A voltaic battery, whose exciting fluid is water. They are used for
charging quadrant electrometer needles and similar purposes. They
polarize very quickly and are of high resistance. Hence very small
plates in large number can be used without impairing their advantage.

Rowland's water battery dispenses with cups and uses capillarity
instead. The zinc and platinum or copper plates of a couple are placed
very close together, while the couples are more distant. On dipping into
water each couple picks up and retains by capillarity a little water
between its plates, which forms the exciting fluid. Many hundred couples
can be mounted on a board, and the whole is charged by dipping into
water and at once removing therefrom. It then develops its full
potential difference.




Battery, Wollaston.
The original plunge battery is attributed to Wollaston. He also invented
the battery known by his name, having the disposition shown in the cut,
of zinc Z, surrounded by a thin sheet of copper C; o, o', o", are the
terminals and B, B, the battery jars. Dilute sulphuric acid is used for
exciting fluid.

B. A. U.
Abbreviation for British Association unit, referring generally to the B.
A. unit of resistance.

B. A. Unit of Resistance.
The original ohm used under that name previous to 1884. The Paris
committee of that year recommended as a practical unit what is known as
the legal ohm. (See Ohm, Legal.)
  1  Legal Ohm                 =  1.0112      B. A. Units of Resistance.
  1  B. A. Unit of Resistance  =   .9889      Legal Ohms.
  1  B. A. Unit of Resistance  =   .98651E9   C. G. S. units.

B. E. adj.
British Engineering, a qualification of a set of units, the B. E. units,
having for base the foot and pound. The term is but little used.

Beaumé Hydrometer.
A hydrometer graduated on the following principle:

The zero point corresponds to the specific gravity of water for liquids
heavier than water. A solution of 15 parts of salt in 85 parts of water
corresponds in specific gravity to 15° B., and between that and zero
fifteen equal degrees are laid out. The degrees are carried down below
this point.

The zero points for liquids lighter than water correspond to the
specific gravity of a solution of 10 parts of salt in 90 parts of water.
The specific gravity of water is taken as 10° B. This gives ten degrees
which are continued up the scale.

Becquerel's Laws of Thermoelectricity.
These are stated under the heads, Law of Intermediate Metals and Law of
Successive Temperatures, q. v.

Bed Piece.
In a dynamo or motor the frame carrying it, including often the
standards in which the armature shaft is journaled, and often the yoke
or even entire field magnet core.

Bell, Automatic Electric.
A bell which rings as long as the circuit is closed, having a circuit
breaker operated by its own motion. (See Bell, Electric.)

Synonyms--Trembling Bell--Vibrating Bell.

Bell, Call.
A bell operated by electricity, designed to call attention, as to a
telephone or telegraphic receiver. (See Bell, Electric.)


Bell Call.
A calling device for attracting the attention of any one, consisting of
some type of electric bell.

Bell, Circular.
A gong-shaped bell, whose clapper and general mechanism is within its
cavity or behind it.

Bell, Differentially Wound.
An electric bell, whose magnet is wound differentially so as to prevent


Bell, Electric.
A bell rung by electricity. Generally it is worked by a current exciting
an electro-magnet, attracting or releasing an armature which is attached
to the vibrating or pivoted tongue of the bell. It may be worked by a
distant switch or press-button, q. v., ringing once for each movement of
the distant switch, etc., or it may be of the vibrating bell type as
shown in the cut. When the current is turned on in this case it attracts
the armature. As this moves towards the poles of the magnet it breaks
the circuit by drawing the contact spring, q. v., away from the contact
point, q. v. This opens the circuit, to whose continuity the contact of
these two parts is essential. The hammer, however, by its momentum
strikes the bell and at once springs back. This again makes the contact
and the hammer is reattracted. This action continues as long as the
circuit is closed at any distant point to which it may be carried. The
ordinary vibrating bell is a typical automatic circuit breaker, q. v.,
this type keeping up the ringing as long as the circuit is closed. Other
bells have no electric contact and simply ring once every time the
circuit is closed. Others worked by an alternating current ring once for
each change of direction of current.


Bell, Electro-mechanical.
A bell which has its striking train operated by a spring or descending
weight, and which train is thrown into action by the release of a detent
or equivalent action by the closing of an electric circuit. It rings for
any given time after being started.

Bell, Indicating.
A bell which by drop-shutter or other indicator connected in circuit
with it, indicates its number or other designation of its call.

Bell, Magneto.
An electric bell operated by the alternating current from a magneto
generator. It has a polarized armature and no circuit breaker. The
armature is attracted first in one direction and then in the other, as
the current alternates and reverses the polarity of the electro-magnet.

Bell, Relay.
A bell operated by a relay circuit.

In polarized relay the adjustment of the tongue to lie normally against
one or the other contact. (See Relay, Polarized.)



Bifilar Winding.
The method followed in winding resistance coils to prevent them from
creating fields of force. The wire is doubled, and the doubled wire
starting with the bend or bight is wound into a coil. The current going
in opposite senses in the two lays of the winding produces no field of

Binary Compound.
A chemical compound whose molecule contains only two elements, such as
water (H2 0), lead oxide (Pb 0), and many others.

In a dynamo or motor armature the wire wound around the coils to secure
them in place and prevent their disturbance by centrifugal action.




Binding Posts or Screws.
Arrangements for receiving the loose end of a wire of an electric
circuit, and securing such end by a screw. Several constructions are
used, as shown here. Sometimes the wire is passed through a hole, and a
screw tapped in at right angles to the hole is screwed down upon the
wire. Sometimes the wire is clamped between two shoulders, one on the
screw, the other on the post. The screw is often a flat-headed thumb
screw or has a milled edge. Sometimes the screw has a slot and is turned
by a screw-driver.

Several openings are often provided in the same post for different

The case containing a mariner's compass on shipboard. It is enclosed
completely; it has a glass side or window through which the compass can
be seen, and is provided with one or two lamps arranged to light the
card, while showing as little light as possible outside.


Bioscopy, Electric.
The diagnosis of life and death by the action of the animal system when
subjected to an electric current or electrification.

A metal, one of the elements, atomic weight, 210 ; equivalent, 70;
valency, 3; specific gravity, 9.9. It is a conductor of electricity.
Relative Resistance, compressed, (silver = 1)   87.23
Specific Resistance,   131.2 microhms
Resistance of a wire
  (a) 1 foot long,  weighing 1 grain,     18.44   ohms
  (b) 1 foot long,  1/1000 inch thick,   789.3  "
  (c) 1 meter long, weighing 1 gram,      12.88   "
  (d) 1 meter long, 1 millimeter thick,    1.670   "
Resistance of a 1-inch cube   51.65   microhms
Electro chemical equivalent,   .7350  (Hydrogen = .0105)
(See Thermo-electric Series.)



A pair of telephones arranged with a curved connecting arm or spring, so
that they can be simultaneously applied to both ears. They are
self-retaining, staying in position without the use of the hands.


Blasting, Electric.
The ignition of blasting charges of powder or high explosives by the
electric spark, or by the ignition to incandescence (red or white heat)
of a thin wire immersed in or surrounded by powder. Special influence or
frictional electric machines or induction coils are used to produce
sparks, if that method of ignition is employed. For the incandescent
wire a hand magneto is very generally employed. (See Fuse, Electric.)

The cuts, Figs. 62 and 63, show one form of incandescent wire fuse. The
large wires are secured to the capsule, so that no strand can come upon
the small wire within the cavity.

The cut, Fig. 64, shows a frictional electric machine for igniting spark

Bleaching, Electric.
Bleaching by agents produced or made available by the direct action of
electricity. Thus if a current under proper conditions is sent through a
solution of common salt (sodium chloride), the electrodes being close
together, the salt is decomposed, chlorine going to one pole and sodium
hydrate to the other. The two substances react upon each other and
combine, forming sodium hypochlorite, which bleaches the tissue immersed
in its solution.

Block System.
A system of signalling on railroads. The essence of the system consists
in having signal posts or stations all along the road at distances
depending on the traffic. The space between each two signal posts is
termed a block. From the signal posts the trains in day time are
signalled by wooden arms termed semaphores, and at night by lanterns.
The arms may be moved by hand or by automatic mechanism depending in
part on electricity for carrying out its functions. Thus in the
Westinghouse system the semaphores are moved by pneumatic cylinders and
pistons, whose air valves are opened and shut by the action of solenoid
magnets, q. v. The current of these magnets is short circuited by
passing trains, so as to let the valves close as the train passes the
signal post. The block system causes the semaphore to be set at "danger"
or "caution," as the train enters the next block. Then the following
train is not allowed to enter the block until the safety signal is
shown. The Westinghouse system provides for two semaphores on a post,
one indicating "danger" as long as the train is on the next block; the
other indicating "caution" as long as the train is on the next two
blocks. The rails form part of the circuit, their joints being bridged
by copper wire throughout the block, and being insulated where the
blocks meet.

Block Wire.
In the block system a wire connecting adjacent block-signal towers or
semaphore poles.

A name sometimes given to an electric experiment illustrating the
repulsion of electrified air particles from a point held at high
relative potential. A metallic point, placed on the prime conductor of
an electric friction or influence machine, becomes highly electrified,
and the air becoming excited is repelled and acts upon the candle flame.
If the candle is placed on the conductor and a point held towards it the
repulsion is still away from the point.


Blow-pipe, Electric Arc.
A name sometimes given to devices for using the voltaic arc to produce
local heating effects. The directive action of the magnet may be used to
force out the arc like a blow-pipe flame, or a blast of air may be
directly applied for the same purpose.

A trade name for crystallized copper sulphate, used in Daniell's and
gravity batteries.

Boat, Electric.
A boat propelled by electricity. The electricity drives a motor which
actuates a screw propeller. The current is generally supplied by a
storage battery. When used on rivers charging stations are established
at proper places. When the boat is used as a tender or launch for a
steam ship, such as a war-vessel, the battery is charged by a plant on
board the ship. From their noiselessness electric boats are peculiarly
available for nocturnal torpedo operations, and the universal equipment
of modern war-ships with electric lightning and power plants makes their
use possible at all points. This type is often termed an electric
launch, and most or all electric boats fall under this category.

A spool of wood or other material wound with insulated wire. In a
tangent galvanometer the bobbin becomes a ring, with a channel to
receive the winding. As the ring is not infinitely large compared to the
needle the tangent law is not absolutely fulfilled. It is most
accurately fulfilled (S. P. Thomson) when the depth of the groove or
channel in the radial direction bears to the breadth in the axial
direction the ratio of square root of 3 to the square root of 2 or
approximately 11 : 9

Body Protector.
A metallic short circuit connected with the wrists and lower legs of the
human body, so that if by accident an active circuit is grounded by the
hands and body of the workman wearing it, most of the current will pass
through the wire conductors, thus avoiding the vital organs of the body.

Boiler Feed, Electric.
An apparatus by which an electric current acting on an electro-magnet,
or other equivalent device, opens the water supply when the water level
in a boiler sinks too low, and cuts off the water supply as the water
level rises.

In secondary batteries the escape of hydrogen and oxygen gas when the
battery is charged. The bubbling of the escaping gases produces the
effect of boiling.


An absolute, or c. g. s., unit of momentum; a gram moving at the rate of
one centimeter per second; a gram-kine (see Kine); a unit proposed by
the British Association.

An apparatus for detecting small amounts of radiant energy (radiant
heat, so called). A coil suspended by a fine wire or filament so as to
be free to rotate under the effect of force is made up of two parallel
and equal wires, insulated from each other, but connected so that
parallel currents sent through them go in opposite direction through
each. This coil is hung in a strong electro-magnetic field produced by a
large coil surrounding it. When a current passes through the suspended
coil no effect will follow, because the oppositely wound portions
counteract each other exactly. In the circuit with one half of the
suspended coil is an exceedingly thin strip of platinum wire. The other
half of the coil has no strips. Both halves unite after leaving the
coil. If now the strip of platinum is heated its conductivity is
affected and its half of the coil receives less current than the other
half. This disturbs the balance and the coil swings through a small arc.
This apparatus may be made very sensitive, so that an increase of
temperature of 1/1400º F., 9/70000°C. (1/14000º F.) will be perceptible.
Another construction takes the form of a Wheatstone Bridge, q. v., in
whose arms are introduced resistances consisting of bands of iron, .5
Millimeter wide (.02 inches), .004 millimeter (.00016 inch) thick, and
folded on themselves 14 times so as to make a rectangular grating, 17 x
12 millimeters (.68 x .48 inch). The least difference of heat applied to
the grating affects the galvanometer.

Synonym-Thermic Balance.

Boreal Pole.
The south pointing pole of the magnet. (See Austral Pole.)

A colloquial expression for the English Board of Trade unit of
Electrical Supply. It is formed of the initials of the words "Board of
Trade." (See Unit, Board of Trade.)

Box Bridge.
A constriction of Wheatstone's Bridge in which the necessary resistance
coils are contained in a single box with plugs for throwing the coils in
and out of circuit, and connections to bring the coils into the
different arms of the system. The cut shows a box bridge. Connections
for the galvanometer, battery wires, and terminals of the unknown
resistance are provided, by which its resistances and the connections
are brought into the exact relations indicated in the conventional
diagram of Wheatstone's bridge. (See Wheatstone's Bridge.)

Referring to the cut, the battery wire, say from the zinc plate,
connects at A1, thereby reaching A, its true connecting point. To B1 one
end of the galvanometer circuit or lead is attached, thereby reaching B,
its true connecting point. To C are connected the other end from the
galvanometer and one end of the unknown resistance. The other end of the
unknown resistance, and the other end of the battery wire, in this case
from the carbon plate, connect to D. At G is an infinity plug, as it is
called. When out it breaks the circuit.

In use after the connections are made the key is depressed and the
galvanometer observed. The resistance is changed until no action of the
galvanometer is produced by closing the circuit when the ratio of the
resistances of the arms gives the proportion for calculating the unknown

Synonym--Commercial Wheatstone Bridge, or commercial form of same.



Boxing the Compass.
Naming the thirty-two points of the compass in order, and in sequence to
any point called out at random. There are many exercises in the relative
sailing points and bearings that come under the same head. Thus the
direction of two given points being given by names of the compass
points, it may be required to state the number of points intervening.

Brake, Electro-magnetic.
A brake to stop a wheel from rotating. It comprises a shoe, or sometimes
a ring, which by electro-magnetic attraction is drawn against the
rotating wheel, thus preventing it from turning, or tending to bring it
to rest. (See Electro-magnet, Annular.)



A conductor branching from a main line. Sometimes the term is restricted
to a principal conductor, from which current is distributed.

Branch Block.
In electric wiring of buildings, a block of porcelain or other material
with grooves, holes and screws for the connection of branch wires to a
main wire. Its functions are not only to afford a basis for connecting
the wires, but also to contain safety fuses. As when a branch wire is
taken off, fuses have to be put in its line, the branch block carries
these also. One end of each fuse connects with a main wire, the other
end connects with one of the wires of the branch leader or wire.

Porcelain is a favorite material for them, as the fusing or "blowing
out" of the safety fuses cannot set it on fire.

Branch Conductor.
A parallel or shunt conductor.

Brazing, Electric.
Brazing in which the spelter is melted by means of electricity; either
current incandescence or the voltaic arc may be used. It is identical in
general with electric welding. (See Welding, Electric.)

Branding, Electric.
A system of branding in which the heat of electrically ignited or
incandescent conductors is used to produce or burn in the marks upon the
surface. For the alternating current a small transformer is connected to
or forms part of the tool.


The deposition of a coating of brass by electrolysis. The plating bath
contains both copper and zinc. As anode a plate of brass is used. The
operation must be constantly watched. The deposition of both metals goes
on simultaneously, so  that a virtual alloy is deposited. By changing
the depth of immersion of the anode the color of the deposit is varied.

As a formula for a brassing bath the following are typical. They are
expressed in parts by weight.

(a) For iron and steel.
  Sodium Bisulphate,                 200
  Potassium Cyanide, 70 per cent.,   500
  Sodium Carbonate,                1,000
  Water,                           8,000
  Copper Acetate,                    125
  Zinc Chloride,                     100
  Water,                           2,000
Add the second solution to the first.

(b) For zinc.
  Sodium Bisulphate,                 700
  Potassium Cyanide, 70 per cent., 1,000
  Water,                          20,000
  Copper Acetate,                    350
  Zinc Chloride,                     350
  Aqua Ammoniae,                     400
  Water,                           5,000
Add the second solution to the first.

Use a brass anode; add more zinc to produce a greenish color; more
copper for a red color. A weak current gives a red color; a strong
current lightens the color. The battery power can be altered, a larger
or smaller anode can be used, or a copper or zinc anode can be used to
change the color of the deposit. The bath may vary from 1.036 to 1.100
sp. gr., without harm.

A point where an electric conductor is cut, broken, or opened by a
switch or other device, or simply by discontinuity of the wires.

Break-down Switch.
A switch used in the three-wire system to provide for the discontinuance
of the running of one of the dynamos.

By connecting the positive and negative bus wires to one terminal of the
active dynamo, and the neutral bus wire to the other terminal, one
dynamo will supply the current and the system operates like a two-wire
system, but can only be used for half its normal capacity.

Breaking Weight.
The weight which, applied in tension, will break a prism or cylinder, as
an electric current conductor.


Breath Figures, Electric.
If a conductor is electrified and placed upon a piece of glass, it will
electrify the glass in contact with it by conduction or discharge. On
removing the conductor the glass remains electrified. The localized
electrification is shown by breathing gently on the glass, when a
species of image of the conductor is produced by the condensed moisture.
A coin is often used for conductor.

Breeze, Electric.
A term in medical electricity, used to designate the silent or brush
discharge of high tension electricity. As an instance of its employment,
the electric head bath (see Bath, Electric Head,) may be cited. The
patient forming one electrode, being insulated and connected to one of
the conductors, the other conductor, on being brought near his person,
discharges into his body.

(a) A special bar of copper connecting the dynamos to the bus wire, q. v.,
in electric lighting or power stations.

(b) Wheatstone's bridge, q. v., and its many modifications, all of which
may be consulted throughout these pages.

British Association Bridge.
The type of Wheatstone bridge used by the committee of the association
in determining the B. A. ohm; the meter bridge, q. v.

Broadside Method.
A method of determining the magnetic moment of a magnet. The magnet, n,
s, under examination is fixed so that it is at right angles to the
magnetic meridian, M, R, which passes through its own center and that of
a compass needle. From the deflection of the latter the moment is


In electro-plating the deposition of a mixture or virtual alloy of
copper and tin. In general manipulation it resembles the operation of
depositing gold and silver alloy, or of brassing.

For bronzing the following bath is recommended:

Prepare each by itself (a) a solution of copper phosphate and (b) a
solution of stannous chloride in a solution of sodium pyrophosphate. For
a, dissolve recently precipitated copper phosphate in concentrated
solution of sodium pyrophosphate. For b, add to a saturated solution of
sodium pyrophosphate solution of stannous chloride as long as the
precipitate which is formed dissolves. Of these two solutions add to a
solution of sodium pyrophosphate which contains about 1.75 oz. of the
salt to the quart, until the precipitate appears quickly and of the
desired color. For anodes use cast bronze plates. Sodium phosphate must
be added from time to time; if the deposit is too light add copper
solution, if too dark add tin solution. (W. T. Brannt.)


In electric current generators and motors, the pieces of copper or other
material that bear against the cylindrical surface of the commutator are
thus termed. Many different constructions have been employed. Some have
employed little wheels or discs bearing against and rotating on the
surface of the commutator. A bundle of copper strips is often employed,
placed flatwise. Sometimes the same are used, but are placed edgewise.
Wire in bundles, soldered together at their distant ends have been
employed. Carbon brushes, which are simply rods or slabs of carbon, are
used with much success.

Synonym--Collecting Brush.

Brush, Carbon.
A brush for a dynamo or motor, which consists of a plate or rod of
carbon, held in a brush holder and pressed against the commutator

Brushes, Adjustment of.
In electric current generators and motors, the brushes which bear upon
the commutator when the machine is in action need occasional adjustment.
This is effected by shifting them until sparking between them and the
commutator is nearly or quite suppressed.


Brushes, Lead of.
In a dynamo electric generator, the lead or displacement in advance of
or beyond the position at right angles to the line connecting the poles
of the field magnet, which is given the brushes. In a motor the brushes
are set back of the right angle position, or are given a negative lead.
(See Lag.)


Brush Holders.
The adjustable (generally) clutch or clamps for holding the commutator
brushes of a dynamo, which keep them in contact with the commutator, and
admit of adjustment by shifting backward and forward of the brushes to
compensate for wear. They are connected to and form part of the rocker,
q. v. By rotating the latter the brush-holders and brushes are carried
in one direction or other around the commutator, so as to vary the lead
as required.

Brush, Pilot.
A third brush, used for application to different parts of a revolving
armature commutator to determine the distribution of potential
difference between its different members. (See Curve of Distribution of
Potential in Armature.) One terminal of a volt-meter is connected to one
of the regular brushes, A, of a dynamo; the other to a third brush, p,
which is pressed against different portions of the commutator of the
dynamo. The readings of the volt-meter are plotted in a curve of
distribution of potential.


Brush, Rotating.
Brushes for taking off the current from dynamo commutators, or giving
current connection to motors, whose ends are in the form of rollers
which rotate like little wheels, and press against the commutator

Brush, Third.
A third brush is sometimes provided in a dynamo for regulating purposes.
Applied to a series machine it adjoins one of the regular brushes and
delivers its current to a resistance, to whose further end the regular
circuit is connected. By a sliding connection the resistance is divided
between the third brush circuit and the regular circuit, and by varying
the position of this contact regulation is obtained.

It is to be distinguished from the pilot brush used for determining the
characteristic of the commutator, although based on the same general



Brush, Wire Gauze.
A collecting or commutator brush for a dynamo or motor, which brush is
made of wire gauze rolled up and compressed into shape.

The bending up and distortion of secondary battery plates. It is largely
due to over-exhausting the batteries. Where the E. M. F. is never
allowed to fall below 1.90 volt it is far less liable to occur.

Any fault or trouble in the connections or working of electric

Bug Trap.
A connection or arrangement for overcoming a "bug." It is said that the
terms "bug" and "bug trap" originated in quadruplex telegraphy.

Bunsen Disc.
In photometry, the Bunsen Disc is a piece of paper upon whose centre a
spot is saturated with melted paraffin, or a ring of paraffined surface
surrounds an untouched central spot. If placed in such a position that
it receives an equal illumination on each side, the spot almost
disappears. It is used on the bar photometer. (See Photometer, Bar.)

Synonym--Grease Spot.


Buoy, Electric.
A buoy for use to indicate channels or dangers in harbors and elsewhere,
which carries an electric light, whose current is supplied by cable from
shore. It has been proposed to use glass tubes exhausted of air and
containing mercury, which, as moved by the waves, would produce a
luminous effect. A fifty-candle power incandescent lamp is an approved
source of light.

Burner, Electric Gas.
A gas burner arranged for the flame to be lighted by electricity. It
takes a great variety of forms. In some cases a pair of terminals are
arranged near the flame or a single terminal is placed near the metal
tip, the latter forming one of the terminals. The spark is generally
produced by an induction coil, or a spark coil. The gas may first be
turned on and the spark then passed. Sometimes the turning of the gas
cock of an individual burner makes and breaks a contact as it turns, and
thereby produces simultaneously with the turning on of the gas a spark
which lights it.

Another form is wholly automatic. A pair of electro-magnets are attached
below the base of the burner, one of which, when excited, turns on the
gas, and the other one when it is excited turns it off. At the same time
a spark is produced with the turning on of the gas so that it is
lighted. Thus, by use of a automatic burner, a distant gas burner can be
lighted by turning an electric switch. An out-door lamp may be lighted
from within a house.

The increasing use of electric incandescent lamps, lighted by the
turning of a switch, tends to displace electric gas burners. The latter
have been classified into a number of types depending on their

Burners are sometimes connected in series with leads from an induction
coil. Then the gas is turned on all at once, and a succession of sparks
passed until the gas is all lighted. The ignition is practically

Button, Push.
A species of switch which is actuated by the pressure of a button. In
its normal position the button is pressed outwards by a spring, and the
circuit is open. When pressed inwards, it closes the circuit. When
released it springs backward and opens the circuit again.

They are principally used for ringing bells. If the latter are of the
automatic type, they ring as long as the button is pressed.

For door-bells and room-bells, the button often occupies the center of a
rosette of wood or bronze or other ornamental piece. Sometimes, as shown
in the cut, they are constructed for use on floors to be pressed by the
foot. The general principle of their construction is shown, although the
method of making the contact varies.

Synonym--Press Button.



(a) In a dynamo, the production of shifting and temporary arcs between
the commutator and brushes, which arcs produce heat enough to injure the
parts in question.

(b) In electro-plating, a defect due to too strong a current in
proportion to the strength of solution and area of electrodes. This
gives a black or badly-colored deposit.

Bus Rod.
A copper conductor used in electric lighting or power stations, to
receive the current from all the dynamos. The distributing leads are
connected to the bus wires.

In the three-wire system there are three; in the two-wire system there
are two bus wires.

The name is undoubtedly derived from "omnibus."

The bus wires may be divided into positive, negative, and, in the
three-wire system, neutral bus wires.

Synonyms--Omnibus Rod, Wire, or Bar--Bus Bar, or Wire.

An electric alarm or call produced by a rapid vibration of electric make
and break mechanism, which is often magnified by enclosure in a
resonating chamber, resembling a bell, but which is not struck or
touched by the vibrating parts. Sometimes a square wooden box is used as

Fig. 72. BUZZER.


B. W. G.
Abbreviation for Birmingham Wire Gauge. (See Wire Gauge, Birmingham.)


(a) Abbreviation for Centigrade, as 100 C., meaning 100 Centigrade. (See
Centigrade Scale.)

(b) A symbol of current or of current strength. Thus in the expression
of Ohm's law C = E/R. C indicates current strength or intensity, not in
any fixed unit, but only in a unit of the same order in which E and R
are expressed; E Indicating electro-motive force and R resistance.

(a) Abbreviation for Cablegram, q. v.

(b) v. It is also used as a verb, meaning to transmit a message by
submarine cable.

(c). An insulated electric conductor, of large diameter. It often is
protected by armor or metallic sheathing and may be designed for use as
an aerial, submarine, subterranean or conduit cable. A cable often
contains a large number of separately insulated conductors, so as to
supply a large number of circuits.

Cable, Aerial.
A cable usually containing a large number of separately insulated wires,
and itself insulated. It is suspended in the air. As its weight is
sometimes so great that it could not well sustain it, a suspending wire
is in such cases carried along with it, to which it is suspended by
cable hangers, q. v.

Cable Box.
A box for receiving underground cable ends and connecting the separate
wires of the cable to air-line wires. It is often mounted on a pole,
which forms the starting point of the air-line portion of the system.

Cable, Bunched.
A cable containing a number of separate and individual conductors. In
some forms it consists virtually of two or more small cables laid
tangent to each other and there secured. Thus each in section represents
two or more tangent circles with the interstice solidly filled with the
metal sheathing.

Cable, Capacity of.
The electrostatic capacity of a cable. A cable represents a Leyden jar
or static condenser. The outer sheathing or armor, or even the more or
less moist coating, if it is unarmored, represents one coating. The wire
conductors represent the other coating, and the insulator is the

The capacity of a cable interferes with its efficiency as a conductor of
broken or interrupted currents, such as are used in telegraphy or
telephoning. As each impulse or momentary current is sent into the line,
it has to charge the cable to at least a certain extent before the
effects of the current are perceptible at the other end. Then the cable
has to discharge itself. All this creates a drag or retardation.

The capacity of a cable is used to determine the locality of breaks in
the continuity of the conductors. The capacity per unit of length being
accurately known, it is obvious that, if the conductor breaks without
disturbance of the insulator, the distance of the break from the end can
be ascertained by determining the capacity of the cable from one end.
This capacity will be in proportion to the capacity of a mile, a knot or
any fixed unit, as the distance to the break is to the length used as


Cable Core.
The conductors of a cable. They are generally copper wire. In a
telephone cable they may be very numerous and insulated from each other.
In ocean cables they may be a group of bare wires twisted or laid
together. Sometimes the conductors are arranged for metallic circuits,
each pair being distinguished by special colored windings.

Cable, Duplex.
A cable containing two wires, each with separate insulation, so as to be
virtually two cables, laid and secured parallel and side by side.

Cable, Flat.
A cable, flat in shape, so as to lie closely against a wall or ceiling.

A message which has been transmitted or is to be transmitted by a
submarine cable. It is sometimes called a cable.

Cable Grip.
A grip for holding the end of a cable, when the cable is to be drawn
into a conduit in a subway. It is an attachment to provide the cable
with an eye or loop. Its end is a split socket and embraces the end of
the cable, and is secured thereto by bolts driven through the cable end.
In drawing a cable into a conduit a capstan and rope are often used, and
the rope is secured to the cable end by the grip.



Cable Hanger.
When a heavy electric cable is suspended from poles it often would be
unsafe to trust to its longitudinal strength to support or sustain its
own weight unless the poles were very near together. In such case an
auxiliary or sustaining wire is run along with it, and by clips or
hangers the cable is connected thereto at as frequent intervals as seem
desirable. The contrivance may take the form of a strip of metal
surrounding the cable and carrying a hook or eye through which the
supporting wire passes.

Synonym--Cable Clip.


Cable Hanger Tongs.
Tongs for attaching cable hangers, q.v. They have long handles so as to
be worked from the ground at the middle of a span.

Cable, Suspending Wire of.
A wire by which an aerial cable is in part or entirely suspended. The
cable, being incapable of sustaining its own weight, is secured by clips
or hangers to a wire, strong from pole to pole immediately above it.
(See Cable Hanger.)

Cable Tank.
A tank in which a submarine cable is coiled away on board a cable-laying
ship, or in the factory on shore for the purpose of testing or
watching its insulation. Sometimes, in order to test it under pressures
approximating to those it will be subjected to in practice, the tank is
closed and the portion of cable within it is subjected to hydraulic
pressure. This represents the pressure it will be exposed to in deep

A mineral; zinc silicate; formula Zn2 Si 03, crystalline system,
Orthorhombic; specific gravity, 3.16-3.9.

The crystals often show strong pyroelectric properties.

The determination by experiment or calculation of the value of the
readings of an instrument, such as a galvanometer or eudiometer. Thus if
a tangent galvanometer has its circle graduated in degrees, a table of
the value of tangents corresponding to every reading occurring in
practice would represent a calibration by calculation. A determination
of the current required to produce each deflection would be a
calibration in the more usual sense. Calibration is generally absolute,
as referring to some fixed unit, but it may be relative, as between two
things both of unknown absolute value.

Calibration, Absolute.
The determination of the absolute value of currents producing given
deflections in a galvanometer, or in other instruments the determination
of corresponding values, as the instrument may be a magnetometer,
quadrant electrometer, or other apparatus.

Calibration, Invariable.
Calibration applicable to specially constructed galvanometers, which is
unaffected by the proximity of masses of iron or field magnets. Such
galvanometers must have a constant controlling field. Such is given by a
powerful permanent magnet, whose field is practically unaffected by the
causes named. Or else, in place of a controlling field, a spring maybe
used to which the needle is attached, and which tends to hold it in one


Calibration, Relative.
The determination of the law connecting the various indications of an
instrument, such as the deflections of the needle of a galvanometer,
with the relative causes; in the case of a galvanometer, the strength of
the currents or the electro-motive forces producing them directly or

Call Bell.
A bell rung by pressing a button or otherwise to call the attention of a
person in a distant place. They can be classified into a great variety
of types according to their uses or construction.

Call Button.
A push button used for ringing a call bell, sounding a buzzer, working
an annunciator and for similar purposes. (See Push Button.)

Synonym--Push Button.

Calling Drop.
In a telephone exchange or telegraph office a drop shutter annunciator,
which falls to call the attention of the operator, notifying him that
the line connected to such drop is to be connected to some other

Calorie or Calory.
A practical unit of heat. There are two calories, respectively called
the great and the small calorie, or the kilogram and the gram calorie.
The first is the quantity of heat required to raise the temperature of
one kilogram of water one degree centigrade. The second is the quantity
of heat required to raise the temperature of one gram of water one
degree centigrade.

An apparatus for measuring the quantity of heat evolved or produced by
or under different conditions. Dulong's water calorimeter consists of a
water jacket, and by the increase of temperature of the water and
enclosing vessels the amount of heat produced by anything in the inner
vessels is determined. The amount of ice a heated body will melt is
sometimes made the basis of a calorimeter. The expansion of a fluid, as
water, may be used. In the calorimeter shown in the cut the heat
produced in a conductor by the passage of an electric current is caused
to heat water whose temperature is shown by a thermometer immersed
therein. The increase of temperature and the weight of the water give
the basis for a determination of the heat produced by the current.
Knowing the resistance of the conductor immersed, the watts can be
calculated. This gives the bases for the determination of the
heat-equivalent of electric energy. This is but an imperfect
calorimeter, as it constantly would lose heat by the surrounding
atmosphere, and would cease to operate as a calorimeter when the water
was as hot as the wire normally would be, for then it would not absorb
all the heat.



The generally accepted unit of illuminating power; there are
three kinds in use as standards. (See Candle, Decimal--Candle, German
Standard--Candle, Standard.)

Candle, Concentric.
An electric candle of the Jablochkoff type, having a small solid carbon
inside of an outside tubular carbon, the space between being filled with
refractory material corresponding to the colombin, q. v., of the
ordinary type. The arc springs across from one carbon to the other.

Candle, Debrun.
An arc lamp with approximately parallel carbons. A transverse priming
connects their bases, and the arc starting there at once flies out to
the end.

Candle, Decimal.
A standard of illuminating power, proposed to the Congress of
Electricians of 1889 by Picou. It is one-twentieth of a Viole, or almost
exactly one standard candle. (See Viole's Standard of Illuminating

Candle, Electric.
An arc lamp regulated by simple gravity, or without any feed of the
carbons or special feeding apparatus, generally for the production of an
arc light of low intensity. This definition may be considered too
elastic, and the word may be restricted to parallel carbon lamps in
which the arc springs across from carbon to carbon. For the latter class
an alternating current is used to keep the carbons of equal length. They
are but little used now. Various kinds have been invented, some of which
are given here.

Candle, German Standard.
A standard of illuminating power used in Germany. It is a paraffin
candle, 6 to the pound, 20 millimeters diameter; flame, 56 millimeters
high; rate of consumption, 7.7 grams per hour. Its value is about two
per cent. lower than the English standard candle.


Candle Holder.
A clamp for holding electric candles of the Jablochkoff type. The ones
shown in the cut designed for Jablochkoff  candles comprise a pair of
metallic clamps, each member insulated from the other, and connected as
terminals of the circuit. When the candle is placed in position the
metal pieces press against the carbons of the candle and thus convey the
current. Below each member of the clamps is a binding screw for the line
wire terminals.



Candle, Jablochkoff.
An arc lamp without regulating mechanism, producing an arc between the
ends of parallel carbons. It consists of two parallel rods of carbon,
between which is an insulating layer of non-combustible material called
the colombin. Kaolin was originally employed for this part; later, as
the fusion of this material was found to short- circuit the arc, a
mixture of two parts of calcium sulphate and one of barium sulphate was
used. The carbons are 4 millimeters (.16 inch) thick, and the colombin
is 3 millimeters (.12 inch) wide and two-thirds as thick. A little slip
of carbon is placed across the top, touching both carbons to start the
arc. Once started the candle burns to the end, and cannot be restarted
after ignition, except by placing a short conductor across the ends, as
at first. The Jablochkoff candle may now be considered as virtually
extinct in this country. In France at one time a great number were in

To keep the carbons of equal length an alternating current must always
be used with them. Special alternating combinations were employed in
some cases where a direct current had to be drawn upon.

Candle, Jamin.
An arc lamp with approximately parallel carbons, one of which oscillates
and is controlled by an electro-magnet and armature. A coil of wire is
carried around the carbons to keep the arc steady and in place. The
frame and wire coils have been found unsatisfactory, as causing a

Candle Power.
The amount of light given by the standard candle. The legal English and
standard American candle is a sperm candle burning two grains a minute.
It should have burned some ten minutes before use, and the wick should
be bent over and have a red tip. Otherwise its readings or indications
are useless. A sixteen candle power lamp means a lamp giving the light
of sixteen candles. The candle power is a universal unit of illuminating


Candle Power, Rated.
The candle power of arc lamps is always stated in excess of the truth,
and this may be termed as above. A 2000 candle power lamp really gives
about 800 candles illumination.

Synonym--Nominal Candle Power.

Candle Power, Spherical.
The average candle power of a source of light in all directions. An arc
lamp and an incandescent lamp vary greatly in the intensity of light
emitted by them in different directions. The average of a number of
determinations at various angles, the lamp being moved about into
different positions, is taken for the spherical candle power.

Candle, Standard.
A standard of illuminating power. Unless otherwise expressed the English
standard sperm candle is indicated by this term. (See Candle Power.)

Candle, Wilde.
An arc lamp with approximately parallel carbons. One of the carbons can
rotate through a small arc being pivoted at its base. This oscillation
is regulated by an electro-magnet at its base, and the carbons touch
when no current is passing. They separate a little when the current
passes, establishing an arc. The regulation is comparable to that of a
regular arc lamp.


India rubber; a substance existing in an emulsion or solution in the
juice of certain trees and vines of the tropics, whence it is obtained
by coagulation and drying. The name "rubber" is due to the fact that one
of its earliest uses was for erasing pencil marks by rubbing. It has a
very high value as an insulator. The unworked crude rubber is called
virgin gum; after working over by kneading, it is termed masticated or
pure gum rubber; after mixture with sulphur and heating, it is termed
vulcanized rubber. If enough sulphur is added it becomes hard, and if
black, is termed ebonite; if vermilion or other pigment is also added to
produce a reddish color, it is termed vulcanite. The masticated gum
dissolves more or less completely in naphtha (sp. gr., .850) benzole,
turpentine, chloroform, ether and other similar liquids.. The resistance
per centimeter cube of "Hooper's" vulcanized India rubber, such as is
used in submarine cables is 1.5E16 ohms. The specific inductive capacity
of pure India rubber is 2.34--of vulcanized 2.94 (Schiller).

Synonyms--India Rubber--Rubber.


Capacity, Dielectric.
The capacity of a dielectric in retaining an electrostatic charge; the
same as Specific Inductive Capacity. 'The number expressing it is
sometimes called the dielectric constant. (See Capacity, Specific

Capacity, Electric, or Electrostatic.
The relative capacity of a conductor or system to retain a charge of
electricity with the production of a given difference of potential. The
greater the charge for a given change of potential, or the less the
change of potential for a given charge the greater the capacity. The
measure of its capacity is the amount of electricity required to raise
the potential to a stated amount. The unit of capacity is the farad, q.
v. Electric capacity is comparable to the capacity of a bottle for air.
A given amount of air will raise the pressure more or less, and the
amount required to raise its pressure a stated amount might be taken as
the measure of capacity, and would be strictly comparable to
electrostatic charge and potential change. The capacity, K, is obviously
proportional to the quantity, Q, of the charge at a given potential, E,
and inversely proportional to the potential, E, for a given quantity, Q,
  (1) K == Q/E
  (2) Q = K * E,
or, the quantity required to raise a conductor by a given potential is
equal to the capacity of the conductor or system multiplied by the rise
of potential. The capacity of a conductor depends upon its environments,
such as the nature of the dielectric surrounding it, the proximity of
oppositely charged bodies and other similar factors. (See
Dielectric-Condenser-Leyden jar.)

The dimensions of capacity are found by dividing a quantity of
electricity by the potential produced in the conductor by such

Quantity ( ((M^.5)*(L^1.5)) / T ) / potential ( ((M^.5)*(L^.5)) / T ) = L.

Capacity, Instantaneous.
The capacity of a condenser when connected only for an instant to a
source of electricity. This is in contrast to electric absorption (see
Absorption, Electric), and is capacity without such absorption taking
part in the action.


Capacity of a Telegraph Conductor.
The electric capacity of a telegraphic conductor is identical in quality
with that of any other conductor. It varies in quantity, not only for
different wires, but for the same wire under different environments, as
the wire reacting through the surrounding air or other dielectric upon
the earth, represents one element of a condenser, the earth, in general,
representing the other. Hence, a wire placed near the earth has greater
capacity than one strung upon high poles, although the wires may be
identical in length, material and diameter. The effect of high capacity
is to retard the transmission of intermitting signals. Thus, when--as in
the Morse system--a key is depressed, closing a long telegraph current
and sending a signal into a line, it is at least very probable that a
portion of the electricity travels to the end of the wire with the
velocity of light. But as the wire has to be charged, enough current to
move the relay may not reach the end for some seconds.

Capacity of Polarization of a Voltaic Cell.
The relative resistance to polarization of a voltaic cell, measured by
the quantity of electricity it can supply before polarization. A
counter-electromotive force may be developed, or the acid or other
solution may become exhausted. The quantity of electricity delivered
before this happens depends on the size and type of cell and other

Capacity, Residual.
When two insulated conductors are separated by a dielectric, and are
discharged disruptively by being connected or nearly connected
electrically, on removing the discharger it is found that a slight
charge is present after a short interval. This is the residual charge.
(See Charge, Residual.) Shaking or jarring the dielectric facilitates
the complete discharge. This retaining of a charge is a phenomenon of
the dielectric, and as such, is termed residual capacity. It varies
greatly in different substances. In quartz it is one-ninth what it is in
air. Iceland spar (crystalline calcite) seems to have no residual
capacity. The action of shaking and jarring in facilitating a discharge
indicates a mechanical stress into which the electrostatic polarization
of the conductor has thrown the intervening dielectric.

Capacity, Specific Inductive.
The ratio of the capacity of a condenser when its plates are separated
by any substance to the capacity of the same condenser when its plates
are separated by air.

A static accumulator consists of two conducting surfaces separated by an
insulator. It is found that the capacity of an accumulator for an
electric charge, which varies with or may be rated by the potential
difference to which its conductors will be brought by the given charge,
varies with the nature of the interposed dielectric, and is proportional
to a constant special to each substance. This constant is the specific
inductive capacity of the dielectric.

The same condenser will have a higher capacity as the dielectric is
thinner, other things being equal. But different dielectrics having
different specific inductive capacities, the constant may be determined
by ascertaining the relative thicknesses of layers having the same total
inductive capacity. The thicker the layer, the higher is its specific
inductive capacity.

Thus it is found that 3.2 units thickness of sulphur have the same total
inductive capacity as 1 unit thickness of air. In other words, if
sulphur is interposed between two conducting plates, they may be
separated to over three times the distance that would be requisite to
retain the same capacity in air. Hence, sulphur is the better
dielectric, and air being taken as unity, the specific inductive
capacity of sulphur is 3.2.


The specific inductive capacity of a dielectric varies with the time and
temperature. That of glass rises 2.5 per cent. between 12° C. (53.6° F.)
and 83° C. (181.4° F.). If a condenser is discharged disruptively, it
retains a small residual charge which it can part with later. If a
metallic connection is made between the plates, the discharge is not
instantaneous. Vibration shaking and jarring facilitate the complete
discharge. All this shows that the charge is a phase of the dielectric
itself, and indicates a strained state into which it is brought.

The following table gives the specific inductive capacity of various

                         Specific Inductive Capacity.
Substance                                         Specific
                                                  Inductive   Authority
Vacuum, air at about 0.001 millimeters pressure   0.94 about  Ayrton
Vacuum, air at about 5 millimeters                0.9985      Ayrton
                                                  0.99941     Boltzmann
Hydrogen at about 760 millimeters pressure        0.9997      Boltzmann
                                                  0.9998      Ayrton
Air at about 760 millimeters pressure             1.0         Taken as the
Carbon Dioxide at about 760 millimeters pressure  1.000356    Boltzmann
                                                  1.0008      Ayrton
Olefiant Gas at about 760 millimeters pressure    1.000722    Boltzmann
Sulphur Dioxide at about 760 millimeters pressure 1.0037      Ayrton
Paraffin Wax, Clear                               1.92        Schiller
                                                  1.96        Wüllner
                                                  1.977   Gibson and Barclay
                                                  2.32        Boltzmann
Paraffin Wax, Milky                               2.47        Schiller
India Rubber, Pure                                2.34        Schiller
India Rubber, Vulcanized                          2.94        Schiller
Resin                                             2.55        Boltzmann
Ebonite                                           2.56        Wüllner
                                                  2.76        Schiller
                                                  3.15        Boltzmann
Sulphur                                           2.88 to 3.21  Wüllner
                                                  3.84        Boltzmann
Shellac                                           2.95 to 3.73  Wüllner
Gutta percha                                      4.2
Mica                                              5
Flint Glass, Very light                           6.57        J. Hopkinson
Flint Glass, Light                                6.85        J. Hopkinson
Flint Glass, Dense                                7.4         J. Hopkinson
Flint Glass, Double extra dense                  10.1         J. Hopkinson


Capacity, Unit of.
The unit of capacity is the capacity of a surface which a unit quantity
will raise to a unit potential. The practical unit is the surface which
a coulomb will raise to one volt, and is called the farad, q. v.

Capacity, Storage.
In secondary batteries the quantity of electrical current which they can
supply when charged, without undue exhaustion. It is expressed in
ampere-hours. The potential varies so little during the discharge that
it is assumed to be constant.

The reaction between liquid surfaces of different kinds or between
liquid and solid surfaces due to surface tension. Its phenomena are
greatly modified by electric charging, which alters the surface tension.
Capillarity is the cause of solutions "creeping," as it is termed. Thus
in gravity batteries a crust of zinc sulphate often formed over the edge
of the jar due to the solution creeping and evaporating. As a liquid
withdraws from a surface which it does not wet, creeping as above is
prevented by coating the edge with paraffin wax, something which water
does not moisten. It also causes the liquids of a battery cell to reach
the connections and injure them by oxidation. The solutions creep up in
the pores of the carbons of a battery and oxidize the clamps. To give
good connections a disc of platinum or of lead is used for the contact
as not being attacked. Another way is to dip the upper ends of the dry
and warm carbons into melted paraffin wax, or to apply the wax to the
hot carbons at the top, and melt it in with a hot iron.


(a) One of the elements; atomic weight, 12. It exists in three
allotropic modifications, charcoal, graphite and diamond. In the
graphitic form it is used as an electric current conductor, as in
batteries and for arc lamp, electrodes and incandescent lamp filaments.
It is the only substance which conducts electricity and which cannot be
melted with comparative ease by increase of current. (See Resistance.)

(b) The carbon plate of a battery or rod of an arc lamp. To secure
greater conductivity in lamp carbons, they are sometimes plated with
nickel or with copper.

(c) v. To place carbons in arc lamps. This has generally to be done once
in twenty-four hours, unless the period of burning is very short.

Carbon, Artificial.
For lamps, carbons and battery plates carbons are made by igniting,
while protected from the action of the air, a mixture of carbon dust and
a cementing and carbonizable substance. Lamp black may be added also.
Powdered coke or gas carbon is mixed with molasses, coal tar, syrup, or
some similar carbonaceous liquid. It is moulded into shape. For lamp
carbons the mixture is forced from a vessel through a round aperture or
die, by heavy pressure, and is cut into suitable lengths. For battery
plates it may be simply pressed into moulds. The carbons are ignited in
covered vessels and also covered with charcoal dust, lamp black or its
equivalent. They are heated to full redness for some hours. After
removal and cooling they are sometimes dipped again into the liquid used
for cementing and reignited. Great care in securing pure carbon is
sometimes necessary, especially for lamps. Fine bituminous coal is
sometimes used, originally by Robert Bunsen, in 1838 or 1840;
purification by different processes has since been applied; carbon from
destructive distillation of coal tar has been used. The famous Carré
carbons are made, it is said, from 15 parts very pure coke dust, five
parts calcined lamp-black, and seven or eight parts sugar--syrup mixed
with a little gum. Five hours heating, with subsequent treatment with
boiling caramel and reignition are applied. The latter treatment is
termed "nourishing." Napoli used three parts of coke to one of tar.
Sometimes a core of different carbon than the surrounding tube is


The following are the resistances of Carré's carbons per meter (39.37

Diameter in     Diameter in  Resistance in Ohms.
Millimeters.    Inches.      @ 20° C. (98° F.)
    1           .039           50.000
    2           .078           12.5
    3           .117            5.55
    4           .156            3.125
    5           .195            2.000
    6           .234            1.390
    8           .312             .781
   10           .390             .5
   12           .468             .348
   15           .585             .222
   18           .702             .154
   20           .780             .125

At high temperatures the resistance is about one-third these amounts. A
layer of copper may increase the conductivity one hundred times and
prolong the duration 14 per cent. Thus a layer of copper 1/695
millimeter (1/17300 inch) thick increases the conductivity 4.5 times; a
coating 1/60 millimeter (1/1500 inch) thick increases the conductivity
one hundred and eleven times.

Carbon, Cored.
A carbon for arc lamps with a central core of softer carbon than the
exterior zone. It fixes the position of the arc, and is supposed to give
a steadier light.

Synonym--Concentric Carbon.

Carbon Holders.
In arc lamps, the fixed clamps for holding the ends of the carbons.

The igniting in a closed vessel, protected from air, of an organic
substance so as to expel from it all the constituents except part of
the carbon; destructive distillation. (See Carbonized Cloth.)

Carbonized Cloth.
Cloth cut in discs and heated in vessels protected from the air, until
reduced to carbon. The heating is sometimes conducted in vacuo. They are
placed in a pile in a glass or other insulating tube, and offer a
resistance which can be varied by pressure. The greater the pressure the
less will be the resistance, and vice versa.

Carbon Dioxide.
A compound gas, CO2. It is composed of
  Carbon, 12 parts by weight.
  Oxygen. 32  "
  Specific gravity, 1.524 (Dulong and Berzelins).
  Molecular weight, 44.

It is a dielectric of about the resistance of air. Its specific
inductive capacity at atmospheric pressures is
  1.000356 (Boltzmann).
  1.0008 (Ayrton).

Synonyms--Carbonic Acid--Carbonic Acid Gas.


Carbon, Volatilization of.
In arc lamps the heat is so intense that it is believed that part of the
carbon is volatilized as vapor before being burned or oxidized by the
oxygen of the air. The same volatilization may take place in
incandescent lamps which are overheated.

The standard of artificial illumination used in France. It is the light
yielded by a standard lamp burning 42 grams (648 grains) of colza oil
per hour, with a flame 40 millimeters (1.57 inch) in height. One carcel
is equal to 9.5 to 9.6 candles.

Carcel Lamp.
The lamp giving the standard of illuminating power. The wick is
cylindrical, giving an Argand or central draft flame. It is woven with
75 strands, and weighs 3.6 grams (55.5 grains) per decimeter (3.9
inches) of length. The chimney is 29 centimeters (11.3 inches) high, 47
millimeters (1.88 inch) in diameter at the bottom, contracting just
above the wick to 34 millimeters (1.36 inch).

Carcel Gas Jet.
A standard Argand gas burner, made with proper rating to give the light
of a definite number of carcels illuminating power. Cognizance must be
taken of the quality of the gas as well as of the burner used.

Carrying Capacity.
In a current conductor, its capacity for carrying a current without
becoming unduly heated. It is expressed in amperes. (See Wire Gauge,

The arrangement of Leyden jars in series on insulating supports, as
described below.

Cascade, Charging and Discharging Leyden Jars In.
An arrangement of Leyden jars in series for the purpose of charging and
discharging. They are placed on insulating supports, the inner coating
of one connected with the outer coating of the next one all through the
series. The actual charge received by such a series, the outer coating
of one end jar being grounded, and the inner coating of the other being
connected to a source of high potential, or else the same being
connected to electrodes of opposite potentials is no greater than that
of a single jar, but a much higher potential difference can be developed
without risk of perforating the glass of a jar. The difference of
potential in each jar of the series is equal to the total potential
difference divided by the number of jars. The energy of discharge is
equal to the same fraction of the energy of a single jar charged with
the same quantity.

[Transcriber's note: The equal distribution of potential assumes all the
jars have the same capacity. The charge on all jars is the same since
they are in series.]


Case-hardening, Electric.
The conversion of the surface of iron into steel by applying a proper
carbonaceous material to it while it is heated by an electric current.
It is a superficial cementation process.

Electric osmore; the transfer of substances in solution through porous
membranes under the influence probably of electrolysis, but without
themselves being decomposed.

Cautery, Electric.
An electro-surgical appliance for removing diseased parts, or arresting
hemorrhages, taking the place of the knife or other cutting instrument.
The cautery is a platinum wire heated to whiteness by an electric
current, and when in that condition used to cut off tumors, stop the
flow of blood and parallel operations. The application is painful, but
by the use of anaesthetics pain is avoided, and the healing after the
operation is greatly accelerated.

The heated wire of the cautery can be used for cutting operations in
many cases where excision by a knife would be almost impracticable.

do.--Galvano-thermal, do.

C. C.
A contraction of cubic centimeter. It is often written in small letters,
as 100 c.c., meaning 100 cubic centimeters.

Cell, Constant.
A cell which yields a constant and uniform current under unvarying
conditions. This implies that neither the electro-motive force or the
resistance of the cell shall vary, or else that as the electro-motive
forces run down the resistance shall diminish in proper proportion to
maintain a constant current. There is really no constant cell. The
constancy is greatest when the external resistance is high in proportion
to the internal resistance.

Cell, Electrolytic.
A vessel containing the electrolyte, a liquid decomposable by the
current, and electrodes, arranged for the passage of a decomposing
current. The voltameter, q. v., is an example.

Cell, Standard Voltaic.
A cell designed to be a standard of electro-motive force; one in which
the same elements shall always be present under the same conditions, so
as to develop the same electro-motive force. In use the circuit is
closed only for a very short time, so that it shall not become altered
by polarization or exhaustion.

Cell, Standard Voltaic, Daniell's.
A zinc-copper-copper sulphate couple.
Many forms are used. Sometimes a number of pieces of blotting paper are
interposed between two plates, one of copper--the other of zinc. The
paper next the copper is soaked in copper sulphate solution, and those
next the zinc in zinc sulphate solution, of course before being put
together. Sometimes the ordinary porous cup combination is employed. The
cut shows a modification due to Dr. Fleming (Phil. Mag. S. 5, vol. xx,
p. 126), which explains itself. The U tube is 3/4-inch diameter, and 8
inches long. Starting with it empty the tap A is opened, and the whole U
tube filled with zinc sulphate solution, and the tap A is closed. The
zinc rod usually kept in the tube L is put in place, tightly corking up
its end of the U tube. The cock C is opened, which lowers the level of
the solution in the right-hand limb of the U tube only. The tap B is
opened and the copper sulphate solution is run in, preserving the line
of separation of the two solutions. The copper rod is taken out of its
tube M, and is put in place. India rubber corks are used for both rods.
As the liquids begin to mix the mixture can be drawn off at C and the
sharp line of demarcation re-established. In Dr. Sloane's standard cell
two test tubes are employed for the solutions and a syphon is used to
connect them.

Oxidation of the zinc lowers the E. M. F.; oxidation of the copper
raises it. With solutions of equal sp. gr. the E. M. F. is 1.104 volts.
If the copper sulphate solution is 1.100 sp. gr. and the zinc sulphate
solution 1.400 sp. gr., both at 15° C. (59°F.), the E. M. F. will be
1.074 volt. Clean pure zinc and freshly electrolyzed copper should be



Cell, Standard Voltaic, Latimer Clark's.
A mercury and zinc electrode couple with
mercurous sulphate as excitant and depolarizer. The positive
element is an amalgam of zinc, the negative is pure mercury. Each
element, in a representative form, the H form, is contained in a
separate vessel which communicate by a tube. Over the pure mercury some
mercurous sulphate is placed. Both vessels are filled to above the level
of the connecting tube with zinc sulphate solution, and kept saturated.
It is tightly closed or corked. The E. M. F. at 15° C (59° F.) is 1.438.
Temperature correction

(1 -  (.00077 *(t - 15° C) ) )

t being expressed in degrees centigrade (Rayleigh). A diminution in
specific gravity of the zinc solution increases the E. M. F. The cell
polarizes rapidly and the temperature coefficient is considered too



Cements, Electrical.
A few cements find their use in electrical work. Marine glue,
Chatterton's compound, and sealing wax may be cited.

Employed as a prefix to indicate one-hundredth, as centimeter, the
one-hundredth of a meter; centi-ampere, the one-hundredth of an ampere.

A thermometer scale in use by scientists of all countries and in general
use in many. The temperature of melting ice is 0º; the temperature of
condensing steam is 100° ; the degrees are all of equal length. To
reduce to Fahrenheit degrees multiply by 9 and divide by 5, and add 32
algebraically, treating all readings below 0º as minus quantities. For
its relations to the Reamur scale, see Reamur Scale. Its abbreviation is
C., as 10º C., meaning ten degrees centigrade.

A metric system unit of length; one-hundredth of a meter; 0.3937 inch.
The absolute or c. g. s. unit of length.

Centimeter-gram-second System.
The accepted fundamental or absolute system of units, called the C. G.
S. system. It embraces units of size, weight, time, in mechanics,
physics, electricity and other branches. It is also called the absolute
system of units. It admits of the formation of new units as required by
increased scope or classification. The following are basic units of the
system :

Of length, centimeter;
of mass, gram;
of time, second:
of force, dyne:
of work or energy, erg.

See Dyne, Erg., and other units in general.


Central Station Distribution or Supply.
The system of supplying electric energy in current form from a main
generating plant to a district of a number of houses, factories, etc. It
is in contrast with the isolated plant system in which each house or
factory has its own separate generating installment, batteries or

Centre of Gravity.
A point so situated with respect to any particular body, that the
resultant of the parallel attracting forces between the earth and the
several molecules of the body always passes through it. These are
resultants of the relative moments of the molecules. If a body is
suspended, as by a string, the centre of gravity always lies vertically
under its point of suspension. By two trials the point of intersection
of plumb lines from the point of suspension being determined the centre
of gravity is known. The vertical from the point of support coincides
with the line of direction.

Centre of Gyration.
The centre of gyration with respect to the axis of a rotating body is a
point at which if the entire mass of the body were concentrated its
moment of inertia would remain unchanged. The distance of this point
from the axis is the radius of gyration.

Centre of Oscillation.
The point referred to in a body, suspended or mounted to swing like a
pendulum, at which if all the mass were concentrated, 1t would complete
its oscillations in the same time. The distance from the axis of support
to this point gives the virtual length of the pendulum which the body

Centre of Percussion.
The point in a suspended body, one free to swing like a pendulum, at
which an impulse may be applied, perpendicular to the plane through the
axis of the body and through the axis of support without shock to the
axis. It is identical with the centre of oscillation, q. v., when such
lies within the body.

Centrifugal Force.
The force which draws a body constrained to move in a curved path away
from the centre of rotation. It is really due to a tangential impulse
and by some physicists is called the centrifugal component of tangential
velocity. It has to be provided against in generator and motor
armatures, by winding them with wire or bands to prevent the coils of
wire from spreading or leaving their bed upon the core.


Centrifugal Governor.
The usual type of steam-engine governor. The motion of the engine
rotates a system of weights, which are forced outward by centrifugal
force, and are drawn inwards by gravity or by springs. Moving outwards
they shut off steam, and moving inwards they admit it, thus keeping the
engine at approximately a constant speed. The connections between them
and the steam supply and the general construction vary widely in
different governors.

C. G. S.
Abbreviation or symbol for Centimeter-gram-second, as the C. G. S.
system. (See Centimeter-gram-second System.) It is sometimes expressed
in capitals, as above, and sometimes in small letters, as the c. g. s.
unit of resistance.

Chamber of Incandescent Lamp.
The interior of the bulb of an incandescent lamp. (See Lamp,



Characteristic Curve.
A curve indicating the variations in electro-motive force developed
during the rotations of the armature of a dynamo or other generator of
E. M. F. The term as used in the electrical sense is thus applied,
although the indicator diagram of a steam engine may be termed its
characteristic curve, and so in many other cases. As the amperes taken
from a series generator are increased in number, the E. M. F. rises, it
may be very rapidly up to a certain point, and thereafter more slowly.
To construct the curve coordinates, q. v., are employed. The resistance
of the dynamo and of the outer circuit being known, the current
intensity is measured. To obtain variations in electro-motive force the
external resistance is changed. Thus a number of ampere readings with
varying known resistance are obtained, and for each one an
electro-motive force is calculated by Ohm's law. From these data a curve
is plotted, usually with volts laid off on the ordinate and amperes on
the abscissa.

By other methods other characteristic curves may be obtained, for which
the titles under Curve may be consulted.


Characteristic, Drooping.
A characteristic curve of a dynamo which indicates a fall in voltage
when an excessive current is taken from the dynamo in question. It is
shown strongly in some Brush machines, and is partly due to the
arrangements for cutting out two of the coils as they approach the
neutral line. It is an advantage, as it protects from overheating on
short circuit.

Characteristic, External.
In a dynamo the characteristic curve in which the relations of volts
between terminals to amperes in the outer circuit are plotted. (See
Curve, External Characteristic.)

Characteristic, Internal.
A characteristic curve of a shunt dynamo, in which the relations of
volts to amperes in the shunt circuit is plotted.

Characteristics of Sound.
Of interest, electrically, as affecting the telephone, they comprise:

(1) Pitch, due to frequency of vibrations.

(2) Intensity or loudness, due to amplitude of waves of sound.

(3) Quality or timbre, the distinguishing characteristics of any
specific sound due to overtones, discords, etc., by which the sound is
recognizable from others. The telephone is held by the U. S. courts to
be capable of reproducing the voice by means of the undulatory current.
(See Current, Undulatory.)

The quantity of electricity that is present on the surface of a body or
conductor. If no electricity is supplied, and the conductor is connected
to the earth, it is quickly discharged. A charge is measured by the
units of quantity, such as the coulomb. The charge that a conductor can
retain at a given rise of potential gives its capacity, expressible in
units of capacity, such as the farad. A charge implies the stretching or
straining between the surface of the charged body, and some
complimentary charged surface or surfaces, near or far, of large or
small area, of even or uneven distribution.

Charge. v.
(a) To introduce an electrostatic charge, as to charge a condenser.

(b) To decompose the elements of a secondary battery, q. v., so as to
render it capable of producing a current. Thus, a spent battery is
charged or recharged to enable it to do more work.



Charge, Bound.
A charge of electricity borne by the surface of a body so situated with
reference to another oppositely charged body, that the charge is
imperceptible to ordinary test, will not affect an electroscope nor
leave the surface if the latter is connected to the earth. To discharge
such a body it must be connected to its complimentarily charged body.
The bound charge was formerly called dissimulated or latent electricity.
(See Charge, Free.)

The charge or portion of a charge of a surface which is neutralized
inductively by a neighboring charge of opposite kind. The degree of
neutralization or of binding will depend on the distance of the two
charged surfaces from one another and on the electro-static nature of
the medium intervening, which must of necessity be a dielectric. A
charge not so held or neutralized is termed a free charge. Thus a
surface may be charged and by the approach of a surface less highly
charged may have part of its charge bound. Then if connected to earth.
it will part with its unbound or free charge, but will retain the other
until the binding surface is removed, or until the electricity of such
surface is itself bound, or discharged, or until connection is made
between the two surfaces. Thus a body may have both a bound and a free
charge at the same time.

Charge, Density of.
The relative quantity of electricity upon a given surface. Thus a
charged surface may have an evenly distributed charge or one of even
density, or an unevenly distributed charge or one of uneven density. In
a thunderstorm the earth has a denser charge under the clouds than

Synonym--Electrical Density.

Charge, Dissipation of.
As every body known conducts electricity, it is impossible so to
insulate a surface that it will not lose its charge by leakage. An
absolute vacuum might answer, and Crookes in a high vacuum has retained
a charge against dissipation for years. The gradual loss is termed as

Charge, Distribution of.
The relation of densities of charge on different parts of a charged
body. On a spherical conductor the charge is normally of even
distribution; on other conductors it is unevenly distributed, being of
greatest density at points, edges, and parts of smallest radius of
curvature. Even distribution can also be disturbed by local induction,
due to the presence of oppositely charged bodies.


Charge, Free.
The charge borne by an insulated body, independent of surrounding
objects. Theoretically it is an impossibility. A charge always has its
compliment somewhere in surrounding objects. As a matter of convenience
and convention, where the complimentary charge is so distributed that
its influence is not perceptible the charge is called a free charge. If
connected to earth the free charge will leave the body. If the body is
connected with an electroscope the free charge will affect the same.
(See Charge, Bound.)

Charge, Residual.
When a Leyden jar or other condenser is discharged by the ordinary
method, after a few minutes standing a second discharge of less amount
can be obtained from it. This is due to what is known as the residual
charge. It seems to be connected in some way with the mechanical or
molecular distortion of the dielectric. The jarring of the dielectric
after discharge favors the rapidity of the action, diminishing the time
required for the appearance of the residual charge. The phenomenon, it
will be seen, is analogous to residual magnetism. This charge is the
reciprocal of electric absorption and depends for its amount upon the
nature of the dielectric. (See Absorption, Electric, and Capacity,

Synonym--Electric Residue.

Chatterton's Compound.
A cement used for cementing together layers or sheets of gutta percha,
and for similar purposes in splicing telegraph cables. Its formula is:
  Stockholm Tar,   1 part.
  Resin,           1 part.
  Gutta Percha,    3 parts.
All parts by weight.

Chemical Change.
When bodies unite in the ratio of their chemical equivalents, so as to
represent the satisfying of affinity or the setting free of thermal or
other energy, which uniting is generally accompanied by sensible heat
and often by light, as in the ignition of a match, burning of a candle,
and, when the new compound exhibits new properties distinct from those
of its components, a chemical combination is indicated. More definitely
it is a change of relation of the atoms. Another form of chemical change
is decomposition, the reverse of combination, and requiring or absorbing
energy and producing several bodies of properties distinct from those of
the original compound. Thus in a voltaic battery chemical combination
and decomposition take place, with evolution of electric instead of
thermal energy.

Chemical Equivalent.
The quotient obtained by dividing the atomic weight, q. v., of an
element by its valency, q. v. Thus the atomic weight of oxygen is 16,
its valency is 2. its chemical equivalent is 8. It is the weight of the
element corresponding to a unit weight of hydrogen, either as replacing
it, or combining with it. In electro-chemical calculations the chemical
equivalent is often conveniently used to avoid the necessity of dividing
by the valency when atomic weights are used. The latter is really the
better practice. The atomic weights in the old system of chemical
nomenclature were chemical equivalents.


Chemical Recorder.
A form of telegraphic recorder in which the characters, often of the
Morse alphabet or some similar one, are inscribed on chemically prepared
paper by decomposition affecting the compound with which the paper is
charged. In the original chemical recorder of Bain, the instrument was
somewhat similar to the Morse recorder, except that the motionless
stylus, S, always pressing against the paper was incapable of making any
mark, but being of iron, and the paper strip being impregnated with
potassium ferrocyanide, on the passage of a current a stain of Prussian
blue was produced where the stylus touched the paper. The current passes
from the line by way of the iron stylus, through the paper, and by way
of a brass surface, M, against which the paper is held and is pressed by
the stylus, to the earth. This recorder is extremely simple and has no
part to be moved by the current. The solution in which the paper is
dipped contains a mixture of potassium ferrocyanide and ammonium
nitrate. The object of the latter is to keep the paper moist. In recent
recorders a solution of potassium iodide has been used, which gives a
brown stain of free iodine, when the current passes. This stain
disappears in a few days.


In the cut, R is the roll of paper, B is a tank of solution with roll,
W1, for moistening the paper; M is the brass surface against which the
stylus, S, presses the paper, P P; W, W are feed rollers; T is the
transmitting key, and zk the battery; Pl, Pl are earth plates. The
apparatus is shown duplicated for each end.


The science treating of atomic and molecular relations of the elements
and of chemical compounds of the same.

Chimes, Electric.
An apparatus employed to illustrate the principles of the electrostatic
charge, involving the ringing of bells by electrostatic attraction and
repulsion. It is used in connection with a frictional, or influence
electric machine. Two bells are employed with a button or clapper
suspended between them. One bell is connected to one of the prime
conductors, q. v., of the machine. The other insulated therefrom is
connected to earth, or if an influence machine is used, to the other
prime conductor. The clappers are hung by a silk thread, so as to be
entirely insulated. On working the machine the bells become oppositely
excited. A clapper is attracted to one, then when charged is repelled
and attracted to the other, it gives up its charge and becoming charged
with similar electricity to that of the bell it touches, is repelled and
attracted to the other, and this action is kept up as long as the
excitement continues, the bells ringing continuously.


Chronograph, Electric.
An apparatus for indicating electrically, and thereby measuring, the
lapse of time. The periods measured may be exceedingly short, such as
the time a photographic shutter takes to close, the time required by a
projectile to go a certain distance, and similar periods.

A drum rotated with even and known velocity may be marked by a stylus
pressed upon it by the action of an electro-magnet when a key is
touched, or other disturbance. Then the space between two marks would
give the period elapsing between the two disturbances of the circuit. As
it is practically impossible to secure even rotation of a drum, it is
necessary to constantly measure its rate of rotation. This is effected
by causing a tuning-fork of known rate of vibration to be maintained in
vibration electrically. A fine point or bristle attached to one of its
arms, marks a sinuous line upon the smoked surface of the cylinder. This
gives the basis for most accurately determining the smallest intervals.
Each wave drawn by the fork corresponds to a known fraction of a second.

For projectiles, the cutting of a wire opens a circuit, and the opening
is recorded instead of the closing. By firing so as to cut two wires at
a known distance apart the rate is obtained by the chronograph.



Chutaux's Solution.
A solution for bichromate batteries. It is composed as follows:
  Water,                1,500 parts
  Potassium bichromate,   100 parts
  mercury bisulphate,     100 parts
  66° sulphuric acid,      50 parts.

Circle, Galvanic or Voltaic.
A term for the voltaic circuit; obsolete.


Circle, Magic.
A form of electro-magnet. It is a thick circle of round iron and is used
in connection with a magnetizing coil, as shown, to illustrate
electro-magnetic attraction.


A conducting path for electric currents properly forming a complete path
with ends joined and including generally a generating device of some
kind. Part of the conduction may be true and part electrolytic. (See
Electrolytic Conduction.) The term has become extended, so that the term
is often applied to any portion of a circuit conveniently considered by
itself. The simplest example of a complete circuit would be a circular
conductor. If rotated in the earth's field so as to cut its lines of
force a current would go through it, and it would be an electric
circuit. Another example is a galvanic battery with its ends connected
by a wire. Here the battery generates the current which, by electrolytic
conduction, goes through the battery and by true conduction through the
wire. For an example of a portion of a circuit spoken of as "a circuit"
see Circuit, Astatic.

Circuit, Astatic.
A circuit so wound with reference to the direction of the currents
passing through it that the terrestrial or other lines of force have no
directive effect upon it, one member counteracting the other. It may be
produced by making the wire lie in two closed curves, A and B, each
enclosing an equal area, one of identical shape and disposition with the
other, and with the current circulating in opposite directions in each
one. Thus each circuit represents a magnetizing turn of opposite
polarity and counteracting each other's directive tendency exhibited in
a field of force with reference to an axis a c. Another form of astatic
circuit is shown in Fig. 86. The portions C, D, lying on opposite sides
of the axis of rotation a c, are oppositely acted on by the earth's
directive force as regards the direction of their rotation.

Figs. 86 and 87. ASTATIC CIRCUITS.

Circuit, Branch.
A circuit dividing into two or more parts in parallel with each other.


Circuit Breaker.
Any apparatus for opening and closing a circuit is thus termed, but it
is generally applied to automatic apparatus. A typical circuit breaker
is the hammer and anvil of the induction coil. (See Induction Coil;
Anvil.) Again a pendulum connected to one terminal of a circuit may
swing so as to carry a point on its lower end through a globule of
mercury as it swings, which globule is connected to the other terminal.
A great many arrangements of this character have been devised.

Synonym.--Contact Breaker.

Circuit Breaker, Automatic.
A circuit breaker worked by the apparatus to which it is attached, or
otherwise automatically. (See Induction Coil; Anvil; Bell, Electric.)

Circuit Breaker, File.
A coarsely cut file, forms one terminal of an electric circuit, with a
straight piece of copper or steel for the other terminal. The latter
terminal drawn along the teeth makes and breaks the contact once for
every tooth. The movable piece should have an insulated handle.

Circuit Breaker, Mercury.
A circuit breaker which may be identical in principle, with the
automatic circuit breaker of an induction coil, but in which in place of
the anvil, q. v., a mercury cup is used, into which the end of a wire
dips and emerges as it is actuated by the impulses of the current. Each
dip makes the contact, which is broken as the wire springs back. The
mercury should be covered with alcohol to protect it from oxidation.

Circuit Breaker, Pendulum.
A circuit breaker in which a pendulum in its swing makes and breaks a
contact. It may be kept in motion by clockwork, or by an electro-magnet,
attracting intermittently an armature attached to its rod, the
magnet circuit being opened and closed by the pendulum or circuit
breaker itself. A mercury contact may be used with it.



Circuit Breaker, Tuning Fork.
A circuit breaker in which a tuning fork makes and breaks the circuit.
Each vibration of one of the prongs in one direction makes a contact,
and the reverse vibration breaks a contact. The adjustment is
necessarily delicate, owing to the limited amplitude of the motion of
the fork. The fork is kept in vibration sometimes by an electro-magnet,
which is excited as the circuit is closed by the fork. One leg of the
fork acts as the armature of the magnet, and is attracted according to
its own natural period.

Circuit Breaker, Wheel.
A toothed wheel with a spring bearing against its teeth. One terminal of
a circuit connects with the wheel through its axle, the other connects
with the spring. When the wheel is turned the circuit is opened and
closed once for each tooth. The interstices between teeth on such a
wheel may be filled with insulating material, giving a cylindrical
surface for the contact spring to rub on.


Circuit, Closed.
A circuit whose electric continuity is complete; to make an open circuit
complete by closing a switch or otherwise is to close, complete, or make
a circuit.

Synonyms--Completed Circuit--Made Circuit.

Circuit, Compound.
A circuit characterized by compounding of generating or receiving
devices, as including several separate batteries, or several motors, or
other receiving devices. It is sometimes used to indicate a circuit
having its battery arranged in series. It should be restricted to the
first definition.


Circuit, Derived.
A partial circuit connected to two points of another circuit, so as to
be in parallel with the portion thereof between such two points; a shunt

Synonyms--Shunt Circuit--Derivative Circuit--Parallel Circuit.

Circuit, Electric, Active.
A circuit through which a current passes. The circuit itself need only
be a conducting ring, or endless wire. Generally it includes, as part of
the circuit, a generator of electro-motive force, and through which
generator by conduction, ordinary or electrolytic, the same current goes
that passes through the rest of the circuit. One and the same current
passes through all parts of a series circuit when such current is

A current being produced by electro-motive force, and electromotive
force disappearing in its production in an active circuit, there must be
some source of energy which will maintain electromotive force against
the drain made upon it by the current.

The simplest conception of an active electric circuit is a ring or
endless conductor swept through a field of force so as to cut lines of
force. A simple ring dropped over a magnet pole represents the
simplification of this process. In such a ring a current, exceedingly
slight, of course, will be produced. In this case there is no generator
in the circuit. An earth coil (see Coil, Earth,) represents such a
circuit, with the addition, when experimented with, of a galvanometer in
the circuit.

In practice, a circuit includes a generator such as a battery or dynamo,
and by conductors is led through a continuous path. Electric lamps,
electrolytic cells, motors and the like may be included in it.

The term "circuit" is also applied to portions of a true circuit, as the
internal circuit, or external circuit. A certain amount of elasticity is
allowed in its use. It by no means necessarily indicates a complete
through circuit.

Circuit, Electrostatic.
(a) A circuit through which an electrostatic or high tension discharge
takes place. It is virtually an electric circuit.

(b) The term is applied also to the closed paths of electrostatic lines
of force.

Circuit, External.
The portion of a circuit not included within the generator.

Circuit, Grounded.
A circuit, one of whose members, the return circuit, is represented by
the earth, so that the earth completes the circuit. In telegraphy each
end of the line is grounded or connected to an earth-plate, q. v., or to
the water or gas-pipes, and the current is assumed to go through the
earth on its return. It really amounts to a discharging at one end, and
charging at the other end of the line. The resistance of the earth is
zero, but the resistance of the grounding or connection with the earth
may be considerable.

Synonyms--Ground Circuit--Earth Circuit--Single Wire Circuit.

[Transcriber's note: The resistance of the earth is high enough that
large power system return currents may produce dangerous voltage
gradients when a power line is shorted to the ground. Don't walk near
downed lines!]


Circuit Indicator.
A pocket compass, decomposition apparatus, galvanometer or other device
for indicating the condition of a wire, whether carrying a current or
not, and, if carrying one, its direction, and sometimes roughly
indicating its strength.

Circuit, Internal.
The portion of an electric circuit included within the generator.

Circuit, Line.
The portion of a circuit embracing the main line or conductor, as in a
telegraph circuit the line carried on the poles; distinguished from the
local circuit (see Circuit, Local,) in telegraphy.

Circuit, Local.
In telegraphy, a short circuit with local generator or battery included,
contained within the limits of the office or station and operated by a
relay, q. v. This was the original local circuit; the term is applicable
to any similar arrangement in other systems. Referring to the cut, the
main line circuit includes the main battery, E, Key, P, Relay, R, ground
plates, G, G1. The relay magnet opens and closes the local circuit with
its local battery, L, and sounder magnet, H, with its armature, B. The
minor parts, such as switches, are omitted.


Circuit, Local Battery.
A local circuit worked by and including a local battery in its course.


Circuit, Loop.
A minor circuit introduced in series into another circuit by a cut-out,
or other device, so as to become a portion of the main circuit.

Circuit Loop Break.
A supporter or bracket with two arms for carrying insulators. Its use is
to enable a loop connection to be introduced into a line which is cut,
so as to enable the connection of the ends of the loop to be made, one
to each end of the through wire, which ends are attached, one to each of
the two insulators.

Circuit, Main.
The circuit including the main line and apparatus supplied by the main
battery, as distinguished from the local circuit. (See Circuit, Local.)

Circuit, Main Battery.
The main circuit, including the main or principal battery in its course.

Circuit, Metallic.
A circuit in which the current outside the generator, or similar parts,
is carried on a metallic conductor; a circuit without any ground
circuit. The including of a galvanic battery or electro plating bath
would not prevent the application of the term; its essential meaning is
the omission of the earth as the return circuit.

Circuit, Negative Side of.
The side of a circuit opposite to the positive side. (See Circuit,
Positive Side of) It is defined as the half of a circuit leading to the
positive terminal of the generator.

Circuit, Open.
A circuit with its continuity broken, as by disconnecting a wire from
the battery, or opening a switch; a broken circuit is its synonym. To
open a switch or disconnect or cut the wire is termed opening or
breaking the circuit.

Synonyms--Incomplete Circuit--Broken Circuit.

Circuit, Positive Side of.
This side is such that an observer standing girdled by the current with
his head in the positive side or region, would see the current pass
around him from his right toward his left hand. It is also defined as
the half of the circuit leading to the negative terminal of the

Circuit, Recoil.
The portion of a parallel circuit presenting an alternative path, q. v.,
for a disruptive discharge.

Circuit, Return.
(a) The part of a circuit extending from the generator to the extreme
point in general, upon which no apparatus is placed. In telegraph
systems the ground generally forms the return circuit. The distinction
of return and working circuit cannot always be made.

(b) It may also be defined as the portion of a circuit leading to the
negative terminal of the generator.


Circuits, Forked.
Circuits starting in different paths or directions from one and the same

Circuit, Simple.
A circuit containing a single generator, and single receiver of any
kind, such as a motor or sounder, with a single connecting conductor. It
is also used to indicate arrangement in multiple arc, but not generally,
or with approval.

Circuits, Parallel.
Two or more conductors starting from a common point and ending at
another common point are termed, parallel circuits, although really but
parts of circuits. If of equal resistance their joint resistance is
obtained by dividing the resistance of one by the number of parallel
circuits. If of unequal resistance r, r', r" , etc., the formula for
joint resistance, R, of two is

R = ( r * r' ) / ( r + r' )

This resistance may then be combined with a third one by the same
formula, and thus any number may be calculated.

Synonym--Shunt Circuit.

Circuit, Voltaic.
Properly a circuit including a conductor and voltaic couple.

It is also applied to the electric circuit, q. v., or to any circuit
considered as a bearer of current electricity.

Circular Units.
Units of area, usually applied to cross sectional area of conductors, by
whose use area is expressed in terms of  circle of unit diameter,
usually a circular mil, which is the area of a circle of one-thousandth
of an inch diameter, or a circular millimeter, which is the area of a
circle of one millimeter diameter. Thus a wire one-quarter of an inch
in diameter has an area of 250 circular mils; a bar one centimeter in
diameter has an area of ten circular millimeters.

[Transcriber's Note: Area is the diameter squared. A 1/4 inch wire has
62500 circular mils of area. A one centimeter (10 millimeter) wire has
100 circular millimeters of area. Actual area = circular mils * (PI/4).]

The product of the total number of conductor turns on the armature of a
dynamo or motor, into the current carried thereby. For two pole machines
it is equal to twice the armature ampere-turns; for four pole machines
to four times such quantity, and so on.

The appliance for grasping and retaining the end of the rod that holds a
carbon in the arc lamp.

Clark's Compound.
A cement used for the outside of the sheath of telegraph cables.
Its formula is:
  Mineral Pitch,   65 parts.
  Silica,          30 parts.
  Tar,              5 parts.
All parts by weight.


A support; a short block of wood, grooved transversely, for holding
electric wires against a wall. For the three wire system three grooves
are used. The entire wiring of apartments is sometimes done by the
"cleat system," using cleats instead of battens, q. v., or mouldings.
The cleats are secured against the wall with the grooves facing it, and
the wires are introduced therein.



Cleat, Crossing.
A cleat with grooves or apertures to support wires which cross each
other. Two or three grooves are transverse, and on the under side, as
above; one groove is longitudinal and on the upper side.

Cleavage, Electrification by.
If a mass of mica is rapidly split in the dark a slight flash is
perceived. Becquerel found that in such separation the two pieces came
away oppositely charged with electricity. The splitting of mica is its

Clock, Controlled.
In a system of electric clocks, the clocks whose movements are
controlled by the current, regulated by the master or controlling clock.

Synonym--Secondary Clock.

Clock, Controlling.
In a system of electric clocks the master clock which controls the
movements of the others, by regulating the current.

Synonym--Master Clock.

Clock, Electric Annunciator.
A clock operating any form of electric annunciator, as dropping
shutters, ringing bells, and the like. It operates by the machinery
closing circuits as required at any desired hour or intervals.


Clock, Electrolytic.
A clock worked by the electrolytic deposition and resolution of a
deposit of metal upon a disc. It is the invention of Nikola Tesla. A
metallic disc is mounted on a transverse axis, so as to readily rotate.
It is immersed in a vessel of copper sulphate. A current is passed
through the bath, the terminals or electrodes being near to and facing
the opposite edges of the disc, so that the line connecting the
electrodes lies in the plane of the disc. If a current is passed through
the solution by the electrodes, copper is deposited on one side of the
disc, and as it rotates under the influence of the weight thus
accumulated on one side, the same metal as it is brought to the other
side of the disc is redissolved. Thus a continuous rotation is
maintained. The cause of the deposition and solution is the position of
the disc; one-half becomes negative and the other positive in their
mutual relations.

Clock, Self-winding Electric.
A clock which is wound periodically by an electric motor and battery.

Clockwork, Feed.
In arc-lamps the system of feeding the carbon or carbons by clockwork
whose movements are controlled by the resistance of the arc. This system
is employed in the Serrin, and in the Gramme regulators, among others.
The carbons, if they approach, move clockwork. The movement of this is
stopped or freed by an electro-magnet placed in shunt around the arc
and carbons.

Partitions or divisions; applied to the winding of electro-magnets and
coils where the winding is put on to the full depth, over single
sections of the core, one section at a time, until the whole core is
filled up.

The closing or completion of a circuit by depressing a key or moving a

In arc lamps a device for the feed of the upper carbons. In its simplest
form it is simply a plate or bar pierced with a hole through which the
carbon passes loosely. The action of the mechanism raises or lowers one
end of the plate or bar. As it rises it binds and clutches the carbon,
and if the action continues it lifts it a little. When the same end is
lowered the carbon and clutch descend together until the opposite end of
the clutch being prevented from further descent, the clutch approaches
the horizontal position and the rod drops bodily through the aperture.
The cut shows the clutches of the Brush double carbon lamp. In practice
the lifting and releasing as regulated by an electro-magnet are so very
slight that practically an almost absolutely steady feed is secured. A
similar clutch is used in the Weston lamp.


Clutch, Electro-magnetic.
A clutch or appliance for connecting a shaft to a source of rotary
motion while the latter is in action. In one form a disc, in whose face
a groove has been formed, which groove is filled with a coil of wire, is
attached to the loose wheel, while the shaft carries a flat plate to act
as armature. On turning on the current the flat plate is attached,
adheres, and causes its wheel to partake of the motion of the shaft.
Contact is made by brushes and collecting rings.

In the cut, A A is the attracted disc; the brushes, B B, take current to
the collecting rings, C. The magnetizing coil is embedded in the body of
the pulley, as shown.




Coatings of a Condenser or Prime Conductor.
The thin conducting coatings of tinfoil, gold leaf or other conducting
substance, enabling the surface to receive and part with the electric
charge readily. Without such a coating the charge and discharge would be
very slow, and would operate by degrees only, as one part of a
non-conducting surface might be densely charged and another part be
quite devoid of sensible charge.

Code, Cipher.
A code of arbitrary words to designate prearranged or predetermined
words, figures or sentences. The systems used in commerce have single
words to represent whole sentences or a number of words of a sentence.
This not only imparts a degree of secrecy, but makes the messages much
shorter. Codes are used a great deal in cable transmission.

Code, Telegraphic.
A telegraphic alphabet. (See Alphabets, Telegraphic.)

In algebra, the numerical multiplier of a symbol, as in the expression
"5x," 5 is the coefficient. In physics, generally a number expressing
the ratio or relation between quantities, one of which is often unity,
as a standard or base of the set of coefficients. Thus the coefficient
of expansion by heat of any substance is obtained by dividing its volume
for a given degree of temperature by its volume at the standard
temperature as 0º C., or 32º F. This gives a fraction by which if any
volume of a substance, taken at 0º C., or at whatever may be taken as
the basic temperature, is multiplied, the expanded volume for the given
change of temperature will be obtained as the product. A coefficient
always in some form implies the idea of a multiplier. Thus the
coefficient of an inch referred to a foot would be 1/12 or .833+,
because any number of inches multiplied by that fraction would give the
corresponding number of feet.

[Transcriber's note: 1/12 is 0.0833+]

Coefficient, Economic.
In machinery, electric generators, prime motors and similar structures,
the number expressing the ratio between energy absorbed by the device,
and useful, not necessarily available, work obtained from it. It is
equal to work obtained divided by energy absorbed, and is necessarily a
fraction. If it exceeded unity the doctrine of the conservation of
energy would not be true. The economic coefficient expresses the
efficiency, q. v., of any machine, and of efficiencies there are several
kinds, to express any one of which the economic coefficient may be used.
Thus, let W--energy absorbed, and w = work produced ; then w/W is the
economic coefficient, and for each case would be expressed numerically.
(See Efficiency, Commercial--Efficiency, Electrical--Efficiency of

The distinction between useful and available work in a dynamo is as
follows: The useful work would include the work expended by the field,
and the work taken from the armature by the belt or other mechanical
connection. Only the latter would be the available work.


Coercive or Coercitive Force.
The property of steel or hard iron, in virtue of which it slowly takes
up or parts with magnetic force, is thus termed ("traditionally";
Daniell). It seems to have to do with the positions of the molecules, as
jarring a bar of steel facilitates its magnetization or accelerates its
parting, when not in a magnetic field, with its permanent or residual
magnetism. For this reason a permanent magnet should never be jarred,
and permitting the armature to be suddenly attracted and to strike
against it with a jar injures its attracting power.

Coercive force is defined also as the amount of negative magnetizing
force required to reduce remnant magnetism to zero.

By some authorities the term is entirely rejected, as the phenomenon
does not seem directly a manifestation of force.

Coil and Coil Plunger.
A device resembling the coil and plunge, q. v., except that for the
plunger of iron there is substituted a coil of wire of such diameter as
to enter the axial aperture of the other, and wound or excited in the
same or in the opposite sense, according to whether attraction or
repulsion is desired.

Coil and Plunger.
A coil provided with a core which is free to enter or leave the central
aperture. When the coil is excited, the core is drawn into it. Various
forms of this device have been used in arc lamp regulators.

Synonym--Sucking coil.




Coil and Plunger, Differential.
An arrangement of coil and plunger in which two plungers or one plunger
are acted on by two coils, wound so as to act oppositely or
differentially on the plunger or plungers. Thus one coil may be in
parallel with the other, and the action on the plunger will then depend
on the relative currents passing through the coils.

Coil, Choking.
A coil of high self-induction, used to resist the intensity of or
"choke" alternating currents. Any coil of insulated wire wound around
upon a laminated or divided iron core forms a choking coil. The iron
coil is usually so shaped as to afford a closed magnetic circuit.

A converter or transformer acts as a choking coil as long as its
secondary is left open. In alternating current work special choking
coils are used. Thus for theatrical work, a choking coil with a movable
iron core is used to change the intensity of the lights. It is in
circuit with the lamp leads. By thrusting in the core the self-induction
is increased and the current diminishes, lowering the lamps; by
withdrawing it the self-induction diminishes, and the current increases.
Thus the lamps can be made to gradually vary in illuminating power like
gas lights, when turned up or down.

Synonyms--Kicking Coil--Reaction Coil.




Coils, Bisected.
Resistance coils with connections at their centers, as shown in the
diagram. They are used for comparing the resistances of two conductors.
The connections are arranged as shown in the coil, each coil being
bisected. For the wires, movable knife-edge contacts are employed. The
principle of the Wheatstone bridge is used in the method and

Coil, Earth.
A coil of wire mounted with commutator to be rotated so as to cut the
lines of force of the earth's magnetic field, thereby generating
potential difference. The axis of rotation may be horizontal, when the
potential will be due to the vertical component of the earth's field, or
the axis may be horizontal, when the potential will be due to the
vertical component, or it may be set at an intermediate angle.

Synonym--Delezenne's Circle.


Coil, Electric.
A coil of wire used to establish a magnetic field by passing a current
through it. The wire is either insulated, or so spaced that its
convolutions do not touch.

Coil, Flat.
A coil whose windings all lie in one plane, making a sort of disc, or an
incomplete or perforated disc.

Coil, Induction.
A coil in which by mutual induction the electromotive force of a portion
of a circuit is made to produce higher or lower electro-motive force, in
an adjoining circuit, or in a circuit, part of which adjoins the
original circuit, or adjoins part of it.

An induction coil comprises three principal parts, the core, the primary
coil and the secondary coil. If it is to be operated by a steady
current, means must be provided for varying it or opening and closing
the primary circuit. A typical coil will be described.


The core is a mass of soft iron preferably divided to prevent extensive
Foucault currents. A cylindrical bundle of soft iron wires is generally
used. Upon this the primary coil of reasonably heavy wire, and of one or
two layers in depth, is wrapped, all being carefully insulated with
shellac and paper where necessary. The secondary coil is wrapped upon or
over the primary. It consists of very fine wire; No. 30 to 36 is about
the ordinary range. A great many turns of this are made. In general
terms the electro-motive force developed by the secondary stands to that
of the primary terminals in the ratio of the windings. This is only

The greatest care is required in the insulating. The secondary is
sometimes wound in sections so as to keep those parts differing greatly
in potential far from each other. This prevents sparking, which would
destroy the insulation.

A make and break, often of the hammer and anvil type, is operated by the
coil. (See Circuit Breaker, Automatic.) As the current passes through
the primary it magnetizes the core. This attracts a little hammer which
normally resting on an anvil completes the circuit. The hammer as
attracted is lifted from the anvil and breaks the circuit. The soft iron
core at once parts with its magnetism and the hammer falls upon the
anvil again completing the circuit. This operation goes on rapidly, the
circuit being opened and closed in quick succession.

Every closing of the primary circuit tends to produce a reverse current
in the secondary, and every opening of the primary circuit tends to
produce a direct current in the secondary. Both are of extremely short
duration, and the potential difference of the two terminals of the
secondary may be very high if there are many times more turns in the
secondary than in the primary.

The extra currents interfere with the action of an induction coil. To
avoid their interference a condenser is used. This consists of two
series of sheets of tin foil. Leaves of paper alternate with the sheets
of tin-foil, the whole being built up into a little book. Each sheet of
tin-foil connects electrically with the sheet next but one to it. Thus
each leaf of a set is in connection with all others of the same set, but
is insulated from the others. One set of leaves of tin-foil connects
with the hammer, the other with the anvil. In large coils there may be
75 square feet of tin-foil in the condenser.

The action of the condenser is to dispose of the direct extra current.
When the primary circuit is opened this current passes into the
condenser, which at once discharges itself in the other direction
through the coil. This demagnetizes the core, and the action intensifies
and shortens the induced current. The condenser prevents sparking, and
in general improves the action of the coil.

Many details enter into the construction of coils, and many variations
in their construction obtain. Thus a mercury cup into which a plunger
dips often replaces the anvil and hammer.


The induction coil produces a rapid succession of sparks, which may
spring across an interval of forty inches. The secondary generally ends
in special terminals or electrodes between which the sparking takes
place. A plate of glass, two inches in thickness, can be pierced by
them. In the great Spottiswoode coil there are 280 miles of wire in the
secondary, and the wire is about No. 36 A.W.G.



Induction coils have quite extended use in electrical work. They are
used in telephone transmitters, their primary being in circuit with the
microphone, and their secondary with the line and receiving telephone.
In electric welding, and in the alternating current system they have
extended application. In all these cases they have no automatic circuit
breaker, the actuating current being of intermittent or alternating


In the cuts the general construction of an induction coil is shown. In
the sectional elevation, Fig. 100, A, is the iron core; B is the primary
of coarse wire; C is a separating tube, which may be of pasteboard; D is
the secondary of fine wire; E, E are the binding posts connected to the
secondary; H, H are the heads or standards; K, K are the terminals of
the primary; F is the vibrating contact spring; G, a standard carrying
the contact screw; J is the condenser with wires, L, M, leading to it.

Referring to the plan, Fig. 101, H represents the primary coil; B and A
are two of the separate sheets of the condenser, each sheet with
projecting ears; G, G are the heads of the coil; the dark lines are
connections to the condenser. One set of sheets connects with the
primary coil at C, and also with the vibrating spring shown in plan and
in the elevation at F. The other set of sheets connects with the post,
carrying the contact screw. The other terminal of the primary runs to a
binding post E. F, in the plan is a binding post in connection with the
standard and contact screw.

Coil, Induction, Inverted.
An induction coil arranged to have a lower electro-motive force in the
secondary than in the primary. This is effected by having more
convolutions in the primary wire than in the secondary. Such coils in
practice are used with the alternating current and then do not include a
circuit breaker or condenser. They are employed in alternating current
system and in electric welding. (See Welding, Electric--Converter.)

In the cut an inverted coil, as constructed for electric welding is
shown. In it the primary coil is marked P; the secondary, merely a bar
of metal, is marked E, with terminals S, S; the heavy coils, I, of iron
wire are the core; K is a screw for regulating the clamps; J, Z is a
second one for the same purpose, while between D and D' the heat is
produced for welding the bars, B, B', held in the clamps, C, C'. It will
be seen how great may be the difference in turns between the single
circle of heavy copper rod or bar which is the secondary of the coil,
and the long coil of wire forming the primary.



Coil, Induction, Telephone.
An induction coil used in telephone circuits. It is placed in the box or
case near the transmitter. The primary is in circuit with the
microphone. The secondary is in circuit with the line and receiving
telephone. In the Bell telephone apparatus the primary of the induction
coil is wound with No. 18 to 24 A. W. G. wire to a resistance of 1/2
ohm; the secondary, with No. 36 wire to a resistance of 80 ohms. The
Edison telephone induction coil was wound with similar wires to a
resistance of 3 to 4 ohms and of 250 ohms respectively.

Coil, Magnetizing.
A coil of insulated wire for making magnets; and for experimental uses;
it has a short axis and central aperture of as small size as consistent
with the diameter of the bar to be magnetized, which has to pass through
it readily. The wire may be quite heavy, 2 or 3 millimeters (.08--.12
inch) thick, and is cemented together with carpenter's glue, or with
shellac or ethereal solution of gum copal. In use it is passed over the
bar a few times while a heavy current is going through it. It is used
for magic circles also. (See Circle, Magic.)


Coil, Resistance.
A coil constructed for the purpose of offering a certain resistance to a
steady current. This resistance may be for the purpose of carrying out
quantitative tests, as in Wheatstone bridge work (see Wheatstone's
Bridge), or simply to reduce the intensity of a current. For the first
class of work the coils are wound so as to prevent the creation of a
magnetic field. This is effected by first doubling the wire without
breaking it, and then starting at the bend the doubled wire, which is
insulated, is wound on a bobbin or otherwise until a proper resistance
is shown by actual measurement. The coils are generally contained or set
in closed boxes with ebonite tops. Blocks of brass are placed on the
top, and one end from one coil and one end from the next connect with
the same block. By inserting a plug, P, so as to connect any two blocks,
which have grooves reamed out for the purpose, the coil beneath will be
short circuited. German silver, platinoid or other alloy, q. v., is
generally the material of the wire. A great object is to have a wire
whose resistance will be unaffected by heat.



Coil, Rhumkorff.
The ordinary induction coil with circuit breaker, for use with original
direct and constant current, is thus termed. (See Coil, Induction.)


Coil, Ribbon.
A coil made of copper ribbon wound flatwise, often into a disc-like
shape, and insulated by tape or strips of other material intervening
between the successive turns.

Coils, Compensating.
Extra coils on the field magnets of dynamos or motors, which coils are
in series with the armature windings for the purpose of keeping the
voltage constant. In compound wound machines the regular series-wound
coil is thus termed. In a separately excited dynamo a coil of the same
kind in circuit with the armature may be used as a compensator.

Coils, Henry's.
An apparatus used in repeating a classic experiment in electro-magnetic
induction, due to Prof. Henry. It consists in a number of coils, the
first and last ones single, the intermediate ones connected in pairs,
and one of one pair placed on the top of one of the next pair. On
opening or closing the circuit of an end coil the induced effect goes
through the series and is felt in the circuit of the other end coil.
Prof. Henry extended the series so as to include seven successive
inductions, sometimes called inductions of the first, second, third and
other orders. Frequently ribbon coils (see Coil, Ribbon,) are used in
these experiments.

Coils, Sectioned.
A device for prolonging the range of magnetic attraction. It consists of
a series of magnetizing coils traversed by an iron plunger. As it passes
through them, the current is turned off the one in the rear or passing
to the rear and turned into the next one in advance. The principle was
utilized in one of Page's electric motors about 1850, and later by
others. The port-electric railroad, q. v., utilizes the same principle.


Collecting Ring.
In some kinds of generators instead of the commutator a pair of
collecting rings of metal, insulated from the machine and from each
other, are carried on the armature shaft. A brush, q. v., presses on
each, and the circuit terminals connect to these two brushes. Such rings
are employed often on alternating current generators, where the current
does not have to be changed or commuted. Collecting rings with their
brushes are used also where a current has to be communicated to a
revolving coil or circuit as in the magnetic car wheel, the cut of which
is repeated here. The coil of wire surrounding the wheel and rotating
with it has to receive current. This it receives through the two
stationary brushes which press upon two insulated metallic rings,
surrounding the shaft. The terminals of the coil connect one to each
ring. Thus while the coil rotates it constantly receives current, the
brushes being connected to the actuating circuit.


(a) A name for the brush, q. v., in mechanical electric generators, such
as dynamos, a pair of which collectors or brushes press on the
commutator or collecting rings, and take off the current.

(b) The pointed connections leading to the prime conductor on a static
machine for collecting the electricity; often called combs. The points
of the combs or collectors face the statically charged rotating glass
plate or cylinder of the machine.

The insulating material between the carbons in a Jablochkoff candle or
other candle of that type. Kaolin was originally used. Later a mixture
of two parts calcium sulphate (plaster of Paris) and one part barium
sulphate (barytes) was substituted.

The colombin was three millimeters (.12 inch) wide, and two millimeters
(.08 inch) thick. (See Candle, Jablochkoff.)

Column, Electric.
An old name for the voltaic pile, made up of a pile of discs of copper
and zinc, with flannel discs, wet with salt solution or dilute acid,
between each pair of plates.


A bar from which a number of teeth project, like the teeth of a comb. It
is used as a collector of electricity from the plate of a frictional or
influence electric machine; it is also used in a lightning arrester to
define a path of very high resistance but of low self-induction, for the
lightning to follow to earth.

The instrument by which telegraph signals are transmitted is sometimes
thus termed.

In general an apparatus for changing. It is used on electric current
generators, and motors, and on induction coils, and elsewhere, for
changing the direction of currents, and is of a great variety of types.

Synonym--Commuter (but little used).


Commutator Bars.
The metallic segments of a dynamo or motor commutator.

Commutator, Flats in.
A wearing away or lowering in level of one or more metallic segments of
a commutator. They are probably due in many cases to sparking, set up by
periodic springing in the armature mounting, or by defective commutator

Commutator of Current Generators and Motors.
In general a cylinder, formed of alternate sections of conducting and
non-conducting material, running longitudinally or parallel with the
axis. Its place is on the shaft of the machine, so that it rotates
therewith. Two brushes, q. v., or pieces of conducting material, press
upon its surface.


As a part of electric motors and generators, its function is to collect
the currents produced by the cutting of lines of force so as to cause
them all to concur to a desired result. The cut shows the simplest form
of commutator, one with but two divisions. Its object may be to enable a
current of constant direction to be taken from a rotating armature, in
which the currents alternate or change direction once in each rotation.
It is carried by the shaft A of the armature and rotates with it. It
consists of two leaves, S S, to which the terminals of the armature are
connected. Two springs, W W, the terminals of the outer circuit, press
against the leaves. The springs which do this take off the current. It
is so placed, with reference to the springs and armature, that just as
the current changes in direction, each leaf changes from one spring to
the other. Thus the springs receive constant direction currents. The
changing action of this commutator appears in its changing the character
of the current from alternating to constant. Were two insulated
collecting rings used instead of a commutator, the current in the outer
circuit would be an alternating one. On some dynamos the commutator has
a very large number of leaves.

Taking the Gramme ring armature, there must be as many divisions of the
commutator as there are connections to the coils. In this case the
function of the commutator is simply to lessen friction, for the brushes
could be made to take current from the coils directly outside of the
periphery of the ring.

Commutator, Split Ring.
A two-division commutator for a motor; it consists of two segments of
brass or copper plate, bent to arcs of a circle, and attached to an
insulating cylinder. They are mounted on the revolving spindle, which
carries the armature, and acts as a two part commutator. For an example
of its application, see Armature, Revolving, Page's. (See also Fig.


An apparatus for utilizing the directive force of the earth upon the
magnetic needle. It consists of a circular case, within which is poised
a magnetized bar of steel. This points approximately to the north, and
is used on ships and elsewhere to constantly show the direction of the
magnetic meridian. Two general types are used. In one the needle is
mounted above a fixed "card" or dial, on which degrees or points of the
compass, q. v., are inscribed. In the other the card is attached to the
needle and rotates with it. The latter represents especially the type
known as the mariner's compass. (See Compass, Mariner's--Compass,
Spirit, and other titles under compass, also Magnetic Axis--Magnetic
Elements.) The needle in good compasses carries for a bearing at its
centre, a little agate cup, and a sharp brass pin is the point of

Compass, Azimuth.
A compass with sights on one of its diameters; used in determining the
magnetic bearing of objects.


Compass Card.
The card in a compass; it is circular in shape, and its centre coincides
with the axis of rotation of the magnetic needle; on it are marked the
points of the compass, at the ends generally of star points. (See
Compass, Points of the.) It may be fixed, and the needle may be poised
above it, or it may be attached to the needle and rotate with it.

Compass, Declination.
An instrument by which the magnetic declination of any place may be
determined. It is virtually a transit instrument and compass combined,
the telescope surmounting the latter. In the instrument shown in the
cut, L is a telescope mounted by its axis, X, in raised journals with
vernier, K, and arc x, for reading its vertical angle, with level n. The
azimuth circle, Q, R, is fixed. A vernier, V is carried by the box, A,
E, and both turn with the telescope. A very light lozenge-shaped
magnetic needle, a, b, is pivoted in the exact centre of the graduated
circles, Q R, and M. The true meridian is determined by any convenient
astronomical method, and the telescope is used for the purpose. The
variation of the needle from the meridian thus determined gives the
magnetic declination.


Compass, Inclination.
A magnetic needle mounted on a horizontal axis at its centre of gravity,
so as to be free to assume the dip, or magnetic inclination, when placed
in the magnetic meridian. It moves over the face of a vertical graduated
circle, and the frame also carries a spirit level and graduated
horizontal circle. In use the frame is turned until the needle is
vertical. Then the axis of suspension of the needle is in the magnetic
meridian. The vertical circle is then turned through 90° of the horizon,
which brings the plane of rotation of the needle into the magnetic
meridian, when it assumes the inclination of the place.


Compass, Mariner's.
A compass distinguished by the card being attached to and rotating with
the needle. A mark, the "lubber's mark" of the sailors is made upon the
case. This is placed so that the line connecting it, and the axis of
rotation of the card is exactly in a plane, passing through the keel of
the ship. Thus however the ship may be going, the point of the card
under or in line with the "lubber's mark," shows how the ship is
pointing. The case of the mariner's compass is often bowl-shaped and
mounted in gimbals, a species of universal joint, so as to bc always
horizontal. (See Compass, Spirit-Gimbals.)


Compass, Points of the.
The circle of the horizon may bc and is best referred to angular
degrees. It has also been divided into thirty-two equiangular and named
points. A point is 11.25°. The names of the points are as follows:
North, North by East, North North-east, North-east by North, North-east,
North-east by East, East North-east, East by North, East, East by South,
East South-east, South-east by East, South-east, South-east by South,
South South-east, South by East, South, South by West, South South-west,
South-west by South, South-west, South-west by West, West South-west,
West by South, West, West by North, West North-west, North-west by West,
North-west, North West by North, North North-west, North by West. They
are indicated by their initials as N. N. W., North North-west, N. by W.,
North by West.

Compass, Spirit.
A form of mariner's compass. The bowl or case is hermetically sealed and
filled with alcohol or other nonfreezing liquid. The compass card is
made with hollow compartments so as nearly to float. In this way the
friction of the pivot or point of support is greatly diminished, and the
compass is far more sensitive.

Compass, Surveyor's.
A species of theodolite; a telescope with collimation lines, mounted
above a compass, so as to be applicable for magnetic surveys. Its use is
to be discouraged on account of the inaccuracy and changes in
declination of the magnetic needle.


Compensating Resistances.
In using a galvanometer shunt the total resistance of the circuit is
diminished so that in some cases too much current flows through it; in
such case additional resistance, termed as above, is sometimes
introduced in series. The shunt in parallel with the galvanometer is
thus compensated for, and the experimental or trial circuit does not
take too much current.

Complementary Distribution.
Every distribution of electricity has somewhere a corresponding
distribution, exactly equal to it of opposite electricity; the latter is
the complimentary distribution to the first, and the first distribution
is also complimentary to it.

A force may always be represented diagrammatically by a straight line,
terminating in an arrow-head to indicate the direction, and of length to
represent the intensity of the force. The line may always be assumed to
represent the diagonal of a parallelogram, two of whose sides are
represented by lines starting from the base of the arrow, and of length
fixed by the condition that the original force shall be the diagonal of
the parallelogram of which they are two contiguous sides; such lines are
called components, and actually represent forces into which the original
force may always be resolved. The components can have any direction.
Thus the vertical component of a horizontal force is zero; its
horizontal component is equal to itself. Its 450 component is equal to
the square root of one-half of its square.

An appliance for storing up electrostatic charges: it is also called a
static accumulator. The telegraphic condenser consists of a box packed
full of sheets of tinfoil. Between every two sheets is a sheet of
paraffined paper, or of mica. The alternate sheets of tinfoil are
connected together, and each set has its own binding post. (See
Accumulator, Electrostatic.)

Condenser, Sliding.
An apparatus representing a Leyden jar whose coatings can be slid past
each other. This diminishes or increases the facing area, and
consequently in almost exactly similar ratio diminishes or increases the
capacity of the condenser.

The conducting power of a given mass of specified material of specified
shape and connections. Conductance varies in cylindrical or prismatic
conductors, inversely as the length, directly as the cross-section, and
with the conductivity of the material. Conductance is an attribute of
any specified conductor, and refers to its shape, length and other
factors. Conductivity is an attribute of any specified material without
direct reference to its shape, or other factors.

The process or act of conducting a current.


The relative power of conducting the electric current possessed by
different substances. A path for the current through the ether is opened
by the presence of a body of proper quality, and this quality, probably
correlated to opacity, is termed conductivity. There is no perfect
conductor, all offer some resistance, q. v., and there is hardly any
perfect non-conductor. It is the reverse and reciprocal of resistance.

Conductivity, Specific.
The reciprocal of specific resistance. (See Resistance--Specific.)

Conductivity, Unit of.
The reciprocal of the ohm; it is a more logical unit, but has never been
generally adopted; as a name the title mho (or ohm written backwards)
has been suggested by Sir William Thomson, and provisionally adopted.

Conductivity, Variable.
The conductivity for electric currents of conductors varies with their
temperature, with varying magnetization, tension, torsion and

In electricity, anything that permits the passage of an electric
current. Any disturbance in the ether takes the form of waves because
the ether has restitutive force or elasticity. In a conductor, on the
other hand, this force is wanting; it opens a path through the ether and
a disturbance advances through it from end to end with a wave front, but
with no succession of waves. This advance is the beginning of what is
termed a current. It is, by some theorists, attributed to impulses given
at all points along the conductor through the surrounding ether, so that
a current is not merely due to an end thrust. If ether waves preclude a
current on account of their restitutive force, ether waves cannot be
maintained in a conductor, hence conductors should be opaque to light,
for the latter is due to ether waves. This is one of the more practical
every day facts brought out in Clerk Maxwell's electromagnetic theory of
light. The term conductor is a relative one, as except a vacuum there is
probably no substance that has not some conducting power. For relative
conducting power, tables of conductivity, q. v., should be consulted.
The metals beginning with silver are the best conductors, glass is one
of the worst.

[Transcriber's note: See "ether" for contemporary comments on this now
discarded concept.]

Conductor, Anti-Induction.
A current conductor arranged to avoid induction from other lines. Many
kinds have been invented and made the subject of patents. A fair
approximation may be attained by using a through metallic circuit and
twisting the wires composing it around each other. Sometimes concentric
conductors, one a wire and the other a tube, are used, insulated, one
acting as return circuit for the other.

Conductor, Conical.
A prime conductor of approximately conical shape, but rounded on all
points and angles. Its potential is highest at the point.


Conductor, Imbricated.
A conductor used in dynamo armatures for avoiding eddy currents, made by
twisting together two or more strips of copper.

Conductor, Prime.
A body often cylindrical or spherical in shape, in any case with no
points or angles, but rounded everywhere, whose surface, if the
conductor itself is not metallic, is made conducting by tinfoil or gold
leaf pasted over it. It is supported on an insulating stand and is used
to collect or receive and retain static charges of electricity.

Conductors, Equivalent.
Conductors of identical resistance. The quotient of the length divided
by the product of the conductivity and cross-section must be the same in
each, if each is of uniform diameter.

Conjugate. adj.
Conjugate coils or conductors are coils placed in such relation that the
lines of force established by one do not pass through the coils of the
other. Hence variations of current in one produce no induced currents in
the other.

Connect. v.
To bring two ends of a conductor together, or to bring one end of a
conductor in connection with another, or in any way to bring about an
electrical connection.

A sleeve with screws or other equivalent device for securing the ends of
wires in electrical contact. A binding-post, q. v., is an example.
Sometimes wire spring-catches are used, the general idea being a device
that enables wires to be connected or released at will without breaking
off or marring their ends. The latter troubles result from twisting
wires together.

Consequent Poles.
A bar magnet is often purposely or accidentally magnetized so as to have
both ends of the same polarity, and the center of opposite polarity. The
center is said to comprise two consequent poles. (See Magnet,

Conservation of Electricity.
As every charge of electricity has its equal and opposite charge
somewhere, near or far, more or less distributed, the sum of negative is
equal always to the sum of positive electrical charges. For this
doctrine the above title was proposed by Lippman.

Contact Breaker.
Any contrivance for closing a circuit, and generally for opening and
closing in quick succession. An old and primitive form consisted of a
very coarsely cut file. This was connected to one terminal, and the
other terminal was drawn over its face, making and breaking contact as
it jumped from tooth to tooth. (See Circuit Breaker--do. Automatic,
etc.--do. Wheel-do. Pendulum.)


Contact, Electric.
A contact between two conductors, such that a current can flow through
it. It may be brought about by simple touch or impact between the ends
or terminals of a circuit, sometimes called a dotting contact, or by a
sliding or rubbing of one terminal on another, or by a wheel rolling on
a surface, the wheel and surface representing the two terminals.

There are various descriptions of contact, whose names are
self-explanatory. The term is applied to telegraph line faults also, and
under this, includes different descriptions of contact with neighboring
lines, or with the earth.

Contact Electricity.
When two dissimilar substances are touched they assume different
electric potentials. If conductors, their entire surfaces are affected;
if dielectrics, only the surfaces which touch each other. (See Contact

Contact Faults.
A class of faults often called contacts, due to contact of the conductor
of a circuit with another conductor. A full or metallic contact is where
practically perfect contact is established; a partial contact and
intermittent contact are self-explanatory.

Contact Point.
A point, pin or stud, often of platinum, arranged to come in contact
with a contact spring, q. v., or another contact point or surface, under
any determined conditions.

Contact Potential Difference.
The potential difference established by the contact of two dissimilar
substances according to the contact theory, q. v.

Contact Series.
An arrangement or tabulation of substances in pairs, each intermediate
substance appearing in two pairs, as the last member of the first, and
first member of the succeeding pair, with the statement of the potential
difference due to their contact, the positively electrified substance
coming first. The following table of some contact potentials is due to
Ayrton and Perry:
Difference of Potential in Volts.
Zinc--Lead        .210
Lead--Tin         .069
Tin--Iron         .313
Iron--Copper      .146
Copper--Platinum  .238
Platinum-Carbon   .113

The sum of these differences is 1.089, which is the contact potential
between zinc and carbon.

Volta's Law refers to this and states that--
  The difference of potential produced by the contact of any two
  substances is equal to the sum of the differences of potentials
  between the intervening substances in the contact series.

It is to be remarked that the law should no longer be restricted to or
stated only for metals.


A spring connected to one lead of an electric circuit, arranged to press
against another spring, or contact point, q. v., under any conditions
determined by the construction of the apparatus. (See Bell,
Electric--Coil, Induction.)

Contact Theory.
A theory devised to explain electrification, the charging of bodies by
friction, or rubbing, and the production of current by the voltaic
battery. It holds that two bodies, by mere contact become oppositely
electrified. If such contact is increased in extent by rubbing together,
the intensity of their electrification is increased. This
electrification is accounted for by the assumption of different kinetic
energy, or energy of molecular motion, possessed by the two bodies;
there being a loss and gain of energy, on the two sides respectively,
the opposite electrifications are the result. Then when separated, the
two bodies come apart oppositely electrified.

The above accounts for the frictional production of electricity. In the
voltaic battery, a separation of the atoms of hydrogen and oxygen, and
their consolidation into molecules occurs, and to such separation and
the opposite electrification of the electrodes by the oxygen and
hydrogen, the current is attributed, because the hydrogen goes to one
electrode, and the oxygen to the other, each giving up or sharing its
own charge with the electrodes to which it goes. If zinc is touched to
copper, the zinc is positively and the copper negatively electrified. In
the separation of hydrogen and oxygen, the hydrogen is positively and
the oxygen negatively electrified. In the battery, the current is due to
the higher contact difference of oxygen and hydrogen compared to that
between zinc and copper. It will be seen that the two contact actions in
a battery work against each other, and that the current is due to a
differential contact action. The zinc in a battery is electrified
negatively because the negative electrification of the oxygen is greater
in amount than its own positive electrification due to contact with the

A muscular spasm or tetanus due to the passage of a current of
electricity; a term in electro-therapeutics.

Controlling Field.
The magnetic or electro-magnetic field, which is used in galvanometers
to control the magnetic needle, tending to restore it to a definite
position whenever it is turned therefrom. It may be the earth's field or
one artificially produced.

Controlling Force.
In galvanometers and similar instruments, the force used to bring the
needle or indicator back to zero. (See Controlling
Field--Electro-Magnetic Control--Gravity Control--Magnetic
Control--Spring Control.)


Convection, Electric.
The production of blasts or currents of air (convection streams) from
points connected to statically charged conductors. The term is sometimes
applied to electric convection of heat. (See Convection of Heat,

Convection, Electrolytic.
The resistance of acidulated water as a true conductor is known to be
very, almost immeasurably, high. As an electrolytic, its resistance is
very much lower. Hence the current produced between immersed electrodes
is theoretically almost null, unless the difference of potential between
them is high enough to decompose the liquid. Yet a feeble current too
great for a true conduction current is sometimes observed when two
electrodes with potential difference too low to cause decomposition are
immersed in it. Such a current is termed an electrolytic convection
current. It is supposed to be due to various causes. Some attribute it
to the presence of free oxygen from the air, dissolved in the water with
which the hydrogen combines. Others attribute it to the diffusion of the
gases of decomposition in the solution; others assume a partial
polarization of the molecules without decomposition. Other theories are
given, all of which are unsatisfactory. The term is due to Helmholtz.

Convection of Heat, Electric.
The effect of a current upon the distribution of heat in an unevenly
heated conductor. In some, such as copper, the current tends to equalize
the varying temperatures; the convection is then said to be positive, as
comparable to that of water flowing through an unequally heated tube. In
others, such as platinum or iron, it is negative, making the heated
parts hotter, and the cooler parts relatively cooler.

The effect of the electric current in affecting the distribution of heat
in unequally heated metal (Thomson's effect. q. v.), is sometimes so
termed. If a current passes through unequally heated iron it tends to
increase the difference of temperature, and the convection is negative;
in copper it tends to equalize the temperature, and the convection is

An induction coil used with the alternating current for changing
potential difference and inversely therewith the available current. They
generally lower the potential, and increase the current, and are placed
between the primary high potential system that connects the houses with
the central station, and the secondary low potential system within the
houses. A converter consists of a core of thin iron sheets, wound with a
fine primary coil of many convolutions, and a coarse secondary coil of
few convolutions. The ratio of convolutions gives the ratio of maximum
potential differences of their terminals between the primary and
secondary coils. The coil may be jacketed with iron to increase the
permeance. (See Alternating Current System.)




Co-ordinates, System of.
A system for indicating the position of points in space by reference to
fixed lines, intersecting at a determined and arbitrary point 0, termed
the origin of co-ordinates. In plane rectangular co-ordinates two lines
are drawn through the origin, one horizontal, termed the axis of
abscissas, or axis of X. All distances measured parallel to it, if
unknown, are indicated by x, and are termed abscissas. The other axis is
vertical, and is termed the axis of ordinates, or axis of Y. All
distances measured parallel to it, if unknown, are indicated by y and
are termed ordinates. Thus by naming its abscissa and ordinate a point
has its position with reference to the axes determined, and by
indicating the relation between a point, line or curve, and a system of
abscissas and ordinates, the properties of a line or curve can be
expressed algebraically. Co-ordinates may also be inclined to each other
at any other angles, forming oblique co-ordinates; relations may be
expressed partly in angles referred to the origin as a centre, giving
polar co-ordinates. For solid geometry or calculations in three
dimensions, a third axis, or axis of Z, is used, distances parallel to
which if unknown are indicated by z.



Cooling Box.
In a hydroelectric machine, q. v., a conduit or chest through which the
steam passes on its way to the nozzles. Its object is to partially
condense the steam so as to charge it with water vesicles whose friction
against the sides of the nozzles produces the electrification .


A metal; one of the elements. Symbol, Cu; atomic weight, 63.5;
equivalent, 63.5 and 31.75; valency, 1 and 2; specific gravity, 8.96.
It is a conductor of electricity, whose conductivity is liable to
vary greatly on account of impurities.

                                                                  Annealed.   Hard drawn.
Relative resistance (Silver = 1),     1.063      1.086
Specific resistance,                  1.598      1.634 microhms.

Resistance of a wire at 0° C. (32° F.),
                                     Annealed.     Hard Drawn.
(a) 1 foot long, weighing 1 grain,     .2041  ohms   .2083  ohms.
(b) 1 foot long, 1/1000 inch thick,   9.612   "     9.831    "
(c) 1 meter long, weighing 1 gram,     .1424  "      .1453   "
(d) 1 meter long, 1 millimeter thick,  .02034 "      .02081  "

                                            microhm.   microhm.
Resistance of 1 inch cube at 0°C. (32° F.)   .6292     .6433

Percentage of resistance change,
per 1° C. (1.8° F.) at about 20° C. (68° F.) = 0.388 per cent.

Electro-chemical Equivalent (Hydrogen = .0105)   Cuprous  .6667
                                                 Cupric   .3334

In electricity it has been very extensively used as the negative plate
of voltaic batteries. It has its most extensive application as
conductors for all classes of electrical leads.

Copper Bath.
A solution of copper used for depositing the metal in the electroplating
process. For some metals, such as zinc or iron, which decompose copper
sulphate solution, special baths have to be used.

The regular bath for copper plating is the following:

To water acidulated with 8 to 10 percent. of sulphuric acid as much
copper sulphate is added as it will take up at the ordinary temperature.
The saturated bath should have a density of 1.21. It is used cold and is
kept in condition by the use of copper anodes, or fresh crystals may be
added from time to time.

For deposition on zinc, iron, tin and other metals more electropositive
than copper, the following baths may be used, expressed in parts by

                     Iron and Steel.   Cast Iron
                     Cold     Hot.     and Zinc.   Zinc.
Sodium Bisulphate,    500     200         300      100
Potassium Cyanide,    500     700         500      700
Sodium Carbonate,    1000     500         ---      ---
Copper Acetate,       475     500         350      450
Aqua Ammoniae,        350     300         200      150
Water,               2500    2500        2500     2500

These are due to Roseleur.


Copper Stripping Bath.
There is generally no object in stripping copper from objects. It can be
done with any of the regular copper baths using the objects to be
stripped as anode. The danger of dissolving the base itself and thereby
injuring the article and spoiling the bath is obvious.

Cord Adjuster.
A device for shortening or lengthening the flexible cord, or flexible
wire supplying the current, and by which an incandescent lamp is
suspended. It often is merely a little block of wood perforated with two
holes through which the wires pass, and in which they are retained in
any desired position by friction and their own stiffness.


Cord, Flexible.
A pair of flexible wire conductors, insulated lightly, twisted together
and forming apparently a cord. They are used for minor services, such as
single lamps and the like, and are designated according to the service
they perform, such as battery cords, dental cords (for supplying dental
apparatus) and other titles.

(a) The conductor or conductors of an electric cable. (See Cable Core.)

(b) The iron mass, generally central in an electro-magnet or armature,
around which the wire is coiled. It acts by its high permeance to
concentrate or multiply the lines of force, thus maintaining a more
intense field. (See Armature--Magnet, Electro--Magnet, Field--Core,
Laminated). In converters or transformers (See Converter) it often
surrounds the wire coils.

Discs of thin wire, for building up armature cores. (See Laminated
Core.) The usual form of core is a cylinder. A number of thin discs of
iron are strung upon the central shaft and pressed firmly together by
end nuts or keys. This arrangement, it will be seen, gives a cylinder as
basis for winding the wire on.

Core-discs, Pierced.
Core-discs for an armature of dynamo or motor, which are pierced around
the periphery. Tubes of insulating material pass through the peripheral
holes, and through these the conductors or windings are carried. The
conductors are thus embedded in a mass of iron and are protected from
eddy currents, and they act to reduce the reluctance of the air gaps.
From a mechanical point of view they are very good. For voltages over
100 they are not advised.

Synonym--Perforated Core-discs.


Core-discs, Segmental.
Core-discs made in segments, which are bolted together to form a
complete disc or section of the core. The plan is adopted principally on
large cores. The discs thus made up are placed together to form the core
exactly as in the case of ordinary one piece discs.


Core-discs, Toothed.
Core-discs of an armature of a dynamo or motor, which discs are cut into
notches on the periphery. These are put together to form the armature
core, with the notches corresponding so as to form a series of grooves
in which the wire winding is laid. This construction reduces the actual
air-gaps, and keeps the wires evenly spaced. Distance-pieces of
box-wood, m, m, are sometimes used to lead the wires at the ends of the


Core, Laminated.
A core of an armature, induction coil or converter or other similar
construction, which is made up of plates insulated more or less
perfectly from each other. The object of lamination is to prevent the
formation of Foucault currents. (See Currents, Foucault.) As insulation,
thin shellacked paper may be used, or sometimes the superficial
oxidation of the plates alone is relied on. The plates, in general, are
laid perpendicular to the principal convolutions of the wire, or
parallel to the lines of force. The object is to break up currents, and
such currents are induced by the variation in intensity of the field of
force, and their direction is perpendicular to the lines of force, or
parallel to the inducing conductors.

A core built up of core discs is sometimes termed a tangentially
laminated core. Made up of ribbon or wire wound coil fashion, it is
termed a radially laminated core.


Core Ratio.
In a telegraph cable the ratio existing between the diameter of the
conducting core and the insulator. To get a ratio approximately accurate
in practical calculations, the diameter of the core is taken at 5 per
cent. less than its actual diameter. The calculations are those
referring to the electric constants of the cable, such as its static
capacity and insulation resistance.

Core, Ribbon.
For discoidal ring-shaped cores of armatures, iron ribbon is often used
to secure lamination and prevent Foucault currents.

Synonym--Tangentially Laminated Core.

Core, Ring.
A core for a dynamo or motor armature, which core forms a complete ring.

Core, Stranded.
In an electric light cable, a conducting core made up of a group of
wires laid or twisted together.

Core, Tubular.
Tubes used as cores for electro-magnets. For very small magnetizing
power, tubular cores are nearly as efficient as solid ones in straight
magnets, because the principal reluctance is due to the air-path. On
increasing the magnetization the tubular core becomes less efficient
than the solid core, as the reluctance of the air-path becomes
proportionately of less importance in the circuit.

The sailors' name for St. Elmo's Fire, q. v.

The practical unit of quantity of electricity. It is the quantity passed
by a current of one ampere intensity in one second. It is equal to 1/10
the C. G. S. electro-magnetic unit of quantity, and to 3,000,000,000 C.
G. S. electrostatic units of quantity. It corresponds to the
decomposition of .0935 milligrams of water, or to the deposition of
1.11815 milligrams of silver.

[Transcriber's note: A coulomb is approximately 6.241E18 electrons. Two
point charges of one coulomb each, one meter apart, exerts a force of
900,000 metric tons.]

Coulomb's Laws of Electrostatic Attraction and Repulsion.
1. The repulsions or attractions between two electrified bodies are in
the inverse ratio of the squares of their distance.

2. The distance remaining the same, the force of attraction or repulsion
between two electrified bodies is directly as the product of the
quantities of electricity with which they are charged.


Counter, Electric.
A device for registering electrically, or by electro-magnetic machinery,
the revolutions of shafts, or any other data or factors.

Counter-electro-motive Force.
A potential difference in a circuit opposed to the main potential
difference, and hence, resisting the operation of the latter, and
diminishing the current which would be produced without it. It appears
in electric motors, which, to a certain extent, operate as dynamos and
reduce the effective electro-motive force that operates them. It
appears in the primary coils of induction coils, and when the secondary
circuit is open, is almost equal to the main electro-motive force, so
that hardly any current can go through them under such conditions. It
appears in galvanic batteries, when hydrogen accumulates on the copper
plate, and in other chemical reactions. A secondary battery is charged
by a current in the reverse direction to that which it would normally
produce. Its own potential difference then appears as a
counter-electro-motive force.

Synonym--Back Electro-motive Force.

Counter-electro-motive Force of Polarization.
To decompose a solution by electrolysis, enough electro-motive force is
required to overcome the energy of composition of the molecule
decomposed. A part of this takes the form of a counter-electromotive
force, one which, for a greater or less time would maintain a current in
the opposite direction if the original source of current were removed.
Thus in the decomposition of water, the electrodes become covered, one
with bubbles of oxygen, the others with bubbles of hydrogen; this
creates a counter E. M. F. of polarization. In a secondary battery, the
working current may be defined as due to this cause.

Synonym--Back Electro-motive Force of Polarization.

Two forces applied to different points of a straight line, when opposed
in direction or unequal in amount, tend to cause rotation about a point
intermediate between their points of application and lying on the
straight line. Such a pair constitute a couple.

Couple, Voltaic or Galvanic.
The combination of two electrodes, and a liquid or liquids, the
electrodes being immersed therein, and being acted on differentially by
the liquid or liquids. The combination constitutes a source of
electro-motive force and consequently of current. It is the galvanic or
voltaic cell or battery. (See Battery, Voltaic--Contact
Theory--Electro-motive Force--Electro-motive Series.)

The joining of cells of a galvanic battery, of dynamos or of other
devices, so as to produce different effects as desired.


Couple, Astatic.
An astatic couple is a term sometimes applied to astatic needles, q.v.

C. P.
(a) An abbreviation of or symbol for candle power, q. v.

(b) An abbreviation of chemically pure. It is used to indicate a high
degree of purity of chemicals. Thus, in a standard Daniell battery, the
use of C. P. chemicals may be prescribed or advised.

The depression that forms in the positive carbon of a voltaic arc. (See
Arc, Voltaic.)

A phenomenon of capillarity, often annoying in battery jars. The
solution, by capillarity, rises a little distance up the sides,
evaporates, and as it dries more creeps up through it, and to a point a
little above it. This action is repeated until a layer of the salts may
form over the top of the vessel. To avoid it, paraffine is often applied
to the edges of the cup, or a layer of oil, often linseed oil, is poured
on the battery solution,

The weight of a litre of hydrogen at 0º C. (32º F.), and 760 mm. (30
inches) barometric pressure. It is .0896 grams. The molecular weight of
any gas divided by 2 and multiplied by the value of the crith, gives the
weight of a litre of the gas in question. Thus a litre of electrolytic
gas, a mixture of two molecules of hydrogen for one of oxygen, with a
mean molecular weight of 12, weighs (12/2) * .0896 or .5376 gram.

Critical Speed.
(a) The speed of rotation at which a series dynamo begins to excite its
own field.

(b) In a compound wound dynamo, the speed at which the same potential is
generated with the full load being taken from the machine, as would be
generated on open circuit, in which case the shunt coil is the only
exciter. The speed at which the dynamo is self-regulating.

(c) In a dynamo the rate of speed when a small change in the speed of
rotation produces a comparatively great change in the electro-motive
force. It corresponds to the same current (the critical current) in any
given series dynamo.

(a) A contact between two electric conductors; qualified to express
conditions as a weather cross, due to rain, a swinging cross when a wire
swings against another, etc.

(b) vb. To make such contact.

Cross-Connecting Board.
A special switch board used in telephone exchanges and central telegraph
offices. Its function is, by plugs and wires, to connect the line wires
with any desired section of the main switchboard. The terminals of the
lines as they enter the building are connected directly to the
cross-connecting board.


Cross Connection.
A method of disposing of the effects of induction from neighboring
circuits by alternately crossing the two wires of a metallic telephone
circuit, so that for equal intervals they lie to right and left, or one
above, and one below.

[Transcriber's note: Also used to cancel the effect of variations in the
ambient magnetic field, such as solar activity.]

Crossing Wires.
The cutting out of a defective section in a telegraph line, by carrying
two wires from each side of the defective section across to a
neighboring conductor, pressing it for the time into service and cutting
the other wire if necessary.

Cross-magnetizing Effect.
A phase of armature interference. The current in an armature of a dynamo
or motor is such as to develop lines of force approximately at right
angles to those of the field. The net cross-magnetizing effect is such
component of these lines, as is at right angles to the lines produced by
the field alone.

Cross-over Block.
A piece of porcelain or other material shaped to receive two wires which
are to cross each other, and hold them so that they cannot come in
contact. It is used in wiring buildings, and similar purposes. (See
Cleat, Crossing.)

Cross Talk.
On telephone circuits by induction or by contact with other wires sound
effects of talking are sometimes received from other circuits; such
effects are termed cross talk.

Crucible, Electric.
A crucible for melting difficultly fusible substances, or for reducing
ores, etc., by the electric arc produced within it. Sometimes the
heating is due more to current incandescence than to the action of an


Crystallization, Electric.
Many substances under proper conditions take a crystalline form. The
great condition is the passage from the fluid into the solid state. When
such is brought about by electricity in any way, the term electric
crystallization may be applied to the phenomenon. A solution of silver
nitrate for instance, decomposed by a current, may give crystals of
metallic silver.


Cup, Porous.
A cup used in two-fluid voltaic batteries to keep the solutions separate
to some extent. It forms a diaphragm through which diffusion inevitably
takes place, but which is considerably retarded, while electrolysis and
electrolytic convection take place freely through its walls. As
material, unglazed pottery is very generally used.

In some batteries the cup is merely a receptacle for the solid
depolarizer. Thus, in the Leclanché battery, the cup contains the
manganese dioxide and graphite in which the carbon electrode is
embedded, but does not separate two solutions, as the battery only uses
one. Nevertheless, the composition of the solution outside and inside
may vary, but such variation is incidental only, and not an essential of
the operation.

The adjustment, or effects of a continuous attempt at readjustment of
potential difference by a conductor, q. v., connecting two points of
different potential. A charged particle or body placed in a field of
force tends to move toward the oppositely charged end or portion of the
field. If a series of conducting particles or a conducting body are held
so as to be unable to move, then the charge of the field tends, as it
were, to move through it, and a current results. It is really a
redistribution of the field and as long as such redistribution continues
a current exists. A current is assumed to flow from a positive to a
negative terminal; as in the case of a battery, the current in the outer
circuit is assumed to flow from the carbon to the zinc plate, and in the
solution to continue from zinc to carbon. As a memoria technica the zinc
may be thought of as generating the current delivering it through the
solution to the carbon, whence it flows through the wire connecting
them. (See Ohm's Law--Maxwell's Theory of Light--Conductor-Intensity.)

[Transcriber's note: Supposing electric current to be the motion of
positive charge causes no practical difficulty, but the current is
actually the (slight) motion of negative electrons.]

Current, After.
A current produced by the animal tissue after it has been subjected to a
current in the opposite direction for some time. The tissue acts like a
secondary battery. The term is used in electro-therapeutics.

Current, Alternating.
Usually defined and spoken of as a current flowing alternately in
opposite directions. It may be considered as a succession of currents,
each of short duration and of direction opposite to that of its
predecessor. It is graphically represented by such a curve as shown in
the cut. The horizontal line may denote a zero current, that is no
current at all, or may be taken to indicate zero electro-motive force.
The curve represents the current, or the corresponding electro-motive
forces. The further from the horizontal line the greater is either, and
if above the line the direction is opposite to that corresponding to the
positions below the line. Thus the current is alternately in opposite
directions, has periods of maximum intensity, first in one and then in
the opposite sense, and between these, passing from one direction to the
other, is of zero intensity. It is obvious that the current may rise
quickly in intensity and fall slowly, or the reverse, or may rise and
fall irregularly. All such phases may be shown by the curve, and a curve
drawn to correctly represent these variations is called the
characteristic curve of such current. It is immaterial whether the
ordinates of the curve be taken as representing current strength or
electromotive force. If interpreted as representing electro-motive
force, the usual interpretation and best, the ordinates above the line
are taken as positive and those below as negative.

Synonyms--Reversed Current--Periodic Currents.



Current, Atomic.
A unit of current strength used in Germany; the strength of a current
which will liberate in 24 hours (86,400 seconds) one gram of hydrogen
gas, in a water voltameter. The atomic current is equal to 1.111
amperes. In telegraphic work the milliatom is used as a unit, comparable
to the milliampere. The latter is now displacing it.

Current, Charge.
If the external coatings of a charged and uncharged jar are placed in
connection, and if the inner coatings are now connected, after
separating them they are both found to be charged in the same manner. In
this process a current has been produced between the outside coatings
and one between the inner ones, to which Dove has given the name Charge
Current, and which has all the properties of the ordinary discharge
current. (Ganot.)

Current, Circular.
A current passing through a circular conductor; a current whose path is
in the shape of a circle.

Current, Commuted.
A current changed, as regards direction or directions, by a commutator,
q. v., or its equivalent.

Current, Constant.
An unvarying current. A constant current system is one maintaining such
a current. In electric series, incandescent lighting, a constant current
is employed, and the system is termed as above. In arc lighting systems,
the constant current series arrangement is almost universal.


Current, Continuous.
A current of one direction only; the reverse of an alternating current.
(See Current, Alternating.)

Current, Critical.
The current produced by a dynamo at its critical speed; at that speed
when a slight difference in speed produces a great difference in
electro-motive force. On the characteristic curve it corresponds to the
point where the curve bends sharply, and where the electro-motive force
is about two-thirds its maximum.

Current, Daniell/U.S. , Daniell/Siemens' Unit.
A unit of current strength used in Germany. It is the strength of a
current produced by one Daniell cell in a circuit of the resistance of
one Siemens' unit. The current deposits 1.38 grams of copper per hour.
It is equal to 1.16 amperes.

Current, Demarcation.
In electro-therapeutics, a current which can be taken from an injured
muscle, the injured portion acting electro-negatively toward the
uninjured portion.

Current Density.
The current intensity per unit of cross-sectional area of the conductor.
The expression is more generally used for electrolytic conduction, where
the current-density is referred to the mean facing areas of the
electrodes, or else to the facing area of the cathode only.

The quality of the deposited metal is intimately related to the current
density. (See Burning.)

              Proper Current Density for Electroplating
           Amperes Per Square Foot of Cathode.--(Urquhart.)
Copper, Acid Bath.                               5.0  to 10.0
"       Cyanide Bath,                            3.0  "   5.0
Silver, Double Cyanide,                          2.0  "   5.0
Gold, Chloride dissolved in Potassium Cyanide,   1.0  "   2.0
Nickel, Double Sulphate,                         6.6  "   8.0
Brass, Cyanide,                                  2.0  "   3.0

Current, Diacritical.
A current, which, passing through a helix surrounding an iron core,
brings it to one-half its magnetic saturation, q. v.

Current, Diaphragm.
If a liquid is forced through a diaphragm, a potential difference
between the liquid on opposite sides of the diaphragm is maintained.
Electrodes or terminals of platinum may be immersed in the liquid, and a
continuous current, termed a diaphragm current, may be taken as long as
the liquid is forced through the diaphragm. The potential difference is
proportional to the pressure, and also depends on the nature of the
diaphragm and on the liquid.


Current, Direct.
A current of unvarying direction, as distinguished from an alternating
current. It may be pulsatory or intermittent in character, but must be
of constant direction.

Current, Direct Induced.
On breaking a circuit, if it is susceptible of exercising
self-induction, q. v., an extra current, in the direction of the
original is induced, which is called "direct" because in the same
direction as the original. The same is produced by a current in one
circuit upon a parallel one altogether separated from it. (See
Induction, Electro-Magnetic-Current, Extra.)

Synonym--Break Induced Current.

Current, Direction of.
The assumed direction of a current is from positively charged electrode
to negatively charged one; in a galvanic battery from the carbon or
copper plate through the outer circuit to the zinc plate and back
through the electrolyte to the carbon or copper plate. (See Current.)

[Transcriber's note: Current is caused by the motion of negative
electrons, from the negative pole to the positive. The electron was
discovered five years after this publication.]

Current, Displacement.
The movement or current of electricity taking place in a dielectric
during displacement. It is theoretical only and can only be assumed to
be of infinitely short duration. (See Displacement, Electric.)

Currents, Eddy Displacement.
The analogues of Foucault currents, hypothetically produced in the mass
of a dielectric by the separation of the electricity or by its
electrification. (See Displacement.)

Current, Extra.
When a circuit is suddenly opened or closed a current of very brief
duration, in the first case in the same direction, in the other case in
the opposite direction, is produced, which exceeds the ordinary current
in intensity. A high potential difference is produced for an instant
only. These are called extra currents. As they are produced by
electro-magnetic induction, anything which strengthens the field of
force increases the potential difference to which they are due. Thus the
wire may be wound in a coil around an iron core, in which case the extra
currents may be very strong. (See Induction, Self-Coil, Spark.)

Current, Faradic.
A term in medical electricity for the induced or secondary alternating
current, produced by comparatively high electro-motive force, such as
given by an induction coil or magneto-generator, as distinguished from
the regular battery current.


Current, Foucault.
A current produced in solid conductors, and which is converted into heat
(Ganot). These currents are produced by moving the conductors through a
field, or by altering the strength of a field in which they are
contained. They are the source of much loss of energy and other
derangement in dynamos and motors, and to avoid them the armature cores
are laminated, the plane of the laminations being parallel to the lines
of force. (See Core, Laminated.)

The presence of Foucault currents, if of long duration, is shown by the
heating of the metal in which they are produced. In dynamo armatures
they are produced sometimes in the metal of the windings, especially if
the latter are of large diameter.

Synonyms--Eddy Currents--Local Currents--Parasitical Currents.

Current, Franklinic.
In electro-therapeutics the current produced by a frictional electric

Current, Induced.
The current produced in a conductor by varying the conditions of a field
of force in which it is placed; a current produced by induction.

Current Induction.
Induction by one current on another or by a portion of a current on
another portion of itself. (See Induction.)

Current Intensity.
Current strength, dependent on or defined by the quantity of electricity
passed by such current in a given time. The practical unit of current
intensity is the ampere, equal to one coulomb of quantity per second of

Current, Inverse Induced.
The current induced in a conductor, when in a parallel conductor or in
one having a parallel component a current is started, or is increased in
strength. It is opposite in direction to the inducing current and hence
is termed inverse. (See Induction, Electro-magnetic.) The parallel
conductors may be in one circuit or in two separate circuits.

Synonyms--Make-induced Current--Reverse-induced Current.

Current, Jacobi's Unit of.
A current which will liberate one cubic centimeter of mixed gases
(hydrogen and oxygen) in a water voltameter per minute, the gases being
measured at 0º C. (32º F.) and 760 mm. (29.92 inches) barometric
pressure. It is equal to .0961 ampere.

Current, Joint.
The current given by several sources acting together. Properly, it
should be restricted to sources connected in series, thus if two battery
cells are connected in series the current they maintain is their joint

Current, Linear.
A current passing through a straight conductor; a current whose path
follows a straight line.


Current, Make and Break.
A succession of currents of short duration, separated by absolute
cessation of current. Such current is produced by a telegraph key, or by
a microphone badly adjusted, so that the circuit is broken at intervals.
The U. S. Courts have virtually decided that the telephone operates by
the undulatory currents, and not by a make and break current. Many
attempts have been made to produce a telephone operating by a
demonstrable make and break current, on account of the above
distinction, in hopes of producing a telephone outside of the scope of
the Bell telephone patent.

[Transcriber's note: Contemporary long distance telephone service is
digital, as this item describes.]

An apparatus for indicating the strength of current. (See Ammeter.)

Current, Negative.
In the single needle telegraph system the current which deflects the
needle to the left.

Current, Nerve and Muscle.
A current of electricity yielded by nerves or muscles. Under proper
conditions feeble currents can be taken from nerves, as the same can be
taken from muscles.

Current, Opposed.
The current given by two or more sources connected in opposition to each
other. Thus a two volt and a one volt battery may be connected in
opposition, giving a net voltage of only one volt, and a current due to
such net voltage.

Current, Partial.
A divided or branch current. A current which goes through a single
conductor to a point where one or more other conductors join it in
parallel, and then divides itself between the several conductors, which
must join further on, produces partial currents. It produces as many
partial currents as the conductors among which it divides. The point of
division is termed the point of derivation.

Synonym--Derived Current.

Current, Polarizing.
In electro-therapeutics, a constant current.

Current, Positive.
In the single needle telegraph system the current which deflects the
needle to the right.

Current, Pulsatory.
A current of constant direction, but whose strength is constantly
varying, so that it is a series of pulsations of current instead of a
steady flow.

Current, Rectified.
A typical alternating current is represented by a sine curve, whose
undulations extend above and below the zero line. If by a simple two
member commutator the currents are caused to go in one direction, in
place of the sine curve a series of short convex curves following one
another and all the same side of the zero line results. The currents all
in the same direction, become what is known as a pulsating current.

Synonym--Redressed Current.


Current, Rectilinear.
A current flowing through a rectilinear conductor. The action of
currents depending on their distance from the points where they act,
their contour is a controlling factor. This contour is determined by the
conductors through which they flow.

Current Reverser.
A switch or other contrivance for reversing the direction of a
current in a conductor.

Currents, Ampérian.
The currents of electricity assumed by Ampere's theory to circulate
around a magnet. As they represent the maintenance of a current or of
currents without the expenditure of energy they are often assumed to be
of molecular dimensions. As they all go in the same sense of rotation
and are parallel to each other the result is the same as if a single set
of currents circulated around the body of the magnet. More will be found
on this subject under Magnetism. The Ampérian currents are purely
hypothetical and are predicated on the existence of a field of force
about a permanent magnet. (See Magnetism, Ampére's Theory of.)

If the observer faces the north pole of a magnet the Ampérian currents
are assumed to go in the direction opposite to that of a watch, and the
reverse for the south pole.


Currents, Angular.
Currents passing through conductors which form an angle with each other.

Currents, Angular, Laws of.
1. Two rectilinear currents, the directions of which form an angle with
each other, attract one another when both approach to or recede from the
apex of the angle.

2. They repel one another, if one approaches and the other recedes from
the apex of the angle.


Currents, Earth.
In long telegraph lines having terminal grounds or connected to earth
only at their ends, potential differences are sometimes observed that
are sufficient to interfere with their working and which, of course, can
produce currents. These are termed earth-currents. It will be noted that
they exist in the wire, not in the earth. They may be of 40 milliamperes
strength, quite enough to work a telegraph line without any battery.
Lines running N. E. and S. W. are most affected; those running N.W. and
S. E. very much less so. These currents only exist in lines grounded at
both ends, and appear in underground wires. Hence they are not
attributable to atmospheric electricity. According to Wilde they are the
primary cause of magnetic storms, q. v., but not of the periodical
changes in the magnetic elements. (See Magnetic Elements.)

Synonym--Natural Currents.

Current, Secondary.
(a) A current induced in one conductor by a variation in the current in
a neighboring one; the current produced in the secondary circuit of an
induction coil or alternating current converter.

(b) The current given by a secondary battery. This terminology is not to
be recommended.

Current, Secretion.
In electro-therapeutics, a current due to stimulation of the secretory

Current Sheet.
(a) If two terminals of an active circuit are connected to two points of
a thin metallic plate the current spreads over or occupies practically a
considerable area of such plate, and this portion of the current is a
current sheet.

The general contour of the current sheet can be laid out in lines of
flux. Such lines resemble lines of force. Like the latter, they are
purely an assumption, as the current is not in any sense composed  of

(b) A condition of current theoretically brought about by the Ampérian
currents in a magnet. Each molecule having its own current, the
contiguous portions of the molecules counteract each other and give a
resultant zero current. All that remains is the outer sheet of electric
current that surrounds the whole.

Current, Sinuous.
A current passing through a sinuous conductor.

Currents, Multiphase.
A term applied to groups of currents of alternating type which
constantly differ from each other by a constant proportion of periods of
alternation. They are produced on a single dynamo, the winding being so
contrived that two, three or more currents differing a constant amount
in phase are collected from corresponding contact rings. There are
virtually as many windings on the armature as there are currents to be
produced. Separate conductors for the currents must be used throughout.

Synonyms--Polyphase Currents--Rotatory Currents.


Currents of Motion.
In electro-therapeutics, the currents produced in living muscle or
nerves after sudden contraction or relaxation.

Currents of Rest.
In electro-therapeutics, the currents traversing muscular or nervous
tissue when at rest. Their existence is disputed.

Currents, Orders of.
An intermittent current passing through a conductor will induce
secondary alternating currents in a closed circuit near it. This
secondary current will induce a tertiary current in a third closed
circuit near it, and so on. The induced currents are termed as of the
first, second, third and other orders. The experiment is carried out by
Henry's coils. (See Coils, Henry's.)

Currents, Thermo-electric.
These currents, as produced from existing thermo-electric batteries,
are generated by low potential, and are of great constancy. The opposite
junctions of the plates can be kept at constant temperatures, as by
melting ice and condensing steam, so that an identical current can be
reproduced at will from a thermopile.

Thermo-electric currents were used by Ohm in establishing his law. (See
Ohm's Law.)

Current, Swelling.
In electro-therapeutics, a current gradually increasing in strength.

Current, Undulatory.
A current varying in strength without any abrupt transition from action
to inaction, as in the make and break current. The current may be
continually changing in direction (see Current, Alternating), and hence,
of necessity, may pass through stages of zero intensity, but such
transition must be by a graduation, not by an abrupt transition. Such
current may be represented by a curve, such as the curve of sines. It is
evident that the current may pass through the zero point as it crosses
the line or changes direction without being a make and break current.
When such a current does alternate in direction it is sometimes called a
"shuttle current." The ordinary commercial telephone current and the
alternating current is of this type. (See Current, Make and Break.)

Current, Unit.
Unit current is one which in a wire of unit length, bent so as to form
an arc of a circle of unit length of radius, would act upon a unit pole
(see Magnetic Pole, Unit,) at the center of the circle with unit force.
Unit length is the centimeter; unit force is the dyne.

[Transcriber's note: The SI definition of an ampere: A current in two
straight parallel conductors of infinite length and negligible
cross-section, 1 metre apart in vacuum, would produce a force equal to
2E-7 newton per metre of length.]


Current, Wattless.
Whenever there is a great difference in phase in an alternating current
dynamo between volts and current, the true watts are much less than the
product of the virtual volts and amperes, because the the watts are
obtained by multiplying the product of the virtual volts and amperes by
the cosine of the angle of lag (or lead). Any alternating current may be
resolved into two components in quadrature with each other, one in phase
with the volts, the other in quadrature therewith, the former is termed
by S. P. Thompson the Working Current, the latter the Wattless Current.
The greater the angle of lag the greater will be the wattless current.

Curve, Arrival.
A curve representing the rate of rise of intensity of current at the end
of a long conductor when the circuit has been closed at the other end.
In the Atlantic cable, for instance, it would require about 108 seconds
for the current at the distant end to attain 9/10 of its full value. The
curve is drawn with its abscissa representing time and its ordinates
current strength.

Curve, Characteristic.
A curve indicating, graphically, the relations between any two factors,
which are interdependent, or which vary simultaneously. Thus in a
dynamo, the voltage increases with the speed of rotation, and a
characteristic curve may be based on the relations between the speed of
rotation and voltage developed. The current produced by a dynamo varies
with the electro-motive force, and a curve can express the relations
between the electro-motive force and the current produced.

A characteristic curve is usually laid out by rectangular co-ordinates
(see Co-ordinates). Two lines are drawn at right angles to each other,
one vertical, and the other horizontal. One set of data are marked off
on the horizontal line, say one ampere, two amperes, and so on, in the
case of a dynamo's characteristic curve.

For each amperage of current there is a corresponding voltage in the
circuit. Therefore on each ampere mark a vertical is erected, and on
that the voltage corresponding to such amperage is laid off. This gives
a series of points, and these points may be connected by a curve. Such
curve will be a characteristic curve.

The more usual way of laying out a curve is to work directly upon the
two axes. On one is laid off the series of values of one set of data; on
the other the corresponding series of values of the other dependent
data. Vertical lines or ordinates, q. v., are erected on the horizontal
line or axis of abscissas at the points laid off; horizontal lines or
abscissas, q. v., are drawn from the points laid off on the vertical
line or axis of ordinates. The characteristic curve is determined by the
intersections of each corresponding pair of abscissa and ordinate.


Variations exist in characteristic curve methods. Thus to get the
characteristic of a commutator, radial lines may be drawn from a circle
representing its perimeter. Such lines may be of length proportional to
the voltage developed on the commutator at the points whence the lines
start. A cut giving an example of such a curve is given in Fig. 125.
(See Curve of Distribution of Potential in Armature.)

There is nothing absolute in the use of ordinates or abscissas. They may
be interchanged. Ordinarily voltages are laid off as ordinates, but the
practise may be reversed. The same liberty holds good for all
characteristic curves. Custom, however, should be followed.



Curve, Characteristic, of Converter.
The characteristic curve of the secondary circuit of an alternating
current converter. It gives by the usual methods (see Curve,
Characteristic,) the relations between the electro-motive force and the
current in the secondary circuit at a fixed resistance. If connected in
parallel a constant electro-motive force is maintained, and the curve is
virtually a straight line. If connected in series an elliptical curve is


Curve, Charging.
In secondary battery manipulation, a curve indicating the increase of
voltage as the charging is prolonged. The rise in voltage with the
duration of the charging current is not uniform. In one case, shown in
the cut, there was a brief rapid rise of about 0.1 volt; then a long
slow rise for 0.15 volt; then a more rapid rise for nearly 0.40 volt,
and then the curve became a horizontal line indicating a cessation of
increase of voltage. The charging rate should be constant.

The horizontal line is laid off in hours, the vertical in volts, so that
the time is represented by abscissas and the voltage by ordinates of the


Curve, Discharging.
A characteristic curve of a storage battery, indicating the fall in
voltage with hours of discharge. The volts may be laid off on the axis
of ordinates, and the hours of discharging on the axis of abscissas. To
give it meaning the rate of discharge must be constant.

Curve, Electro-motive Force.
A characteristic curve of a dynamo. It expresses the relation between
its entire electromotive force, as calculated by Ohm's Law, and the
current intensities corresponding thereto. To obtain the data the dynamo
is driven with different resistances in the external circuit and the
current is measured for each resistance. This gives the amperes. The
total resistance of the circuit, including that of the dynamo, is known.
By Ohm's Law the electro-motive force in volts is obtained for each case
by multiplying the total resistance of the circuit in ohms by the
amperes of current forced through such resistance. Taking the voltages
thus calculated for ordinates and the corresponding amperages for
abscissas the curve is plotted. An example is shown in the cut.


Curve, External Characteristic.
A characteristic curve of a dynamo, corresponding to the electro-motive
force curve, except that the ordinates represent the voltages of the
external circuit, the voltages as taken directly from the terminals of
the machine, instead of the total electro-motive force of the circuit.
The dynamo is run at constant speed. The resistance of the external
circuit is varied. The voltages at the terminals of the machine and the
amperages of current corresponding thereto are determined. Using the
voltages thus determined as ordinates and the corresponding amperages as
abscissas the external characteristic curve is plotted.

This curve can be mechanically produced. A pencil may be moved against a
constant force by two electro-magnets pulling at right angles to each
other. One must be excited by the main current of the machine, the other
by a shunt current from the terminals of the machine. The point of the
pencil will describe the curve.


Curve, Horse Power.
Curves indicating electric horse power. They are laid out with
co-ordinates, volts being laid off on the axis of ordinates, and amperes
on the axis of abscissas generally. The curves are drawn through points
where the product of amperes by volts equals 746. On the same diagram 1,
2, 3 .... and any other horse powers can be plotted if within the
limits. See Fig. 120.

Curve, Isochasmen.
A line drawn on the map of the earth's surface indicating the locus of
equal frequency of auroras.


Curve, Life.
A characteristic curve showing the relations between the durability and
conditions affecting the same in any appliance. It is used most for
incandescent lamps. The hours of burning before failure give ordinates,
and the rates of burning, expressed indirectly in volts or in
candle-power, give abscissas. For each voltage or for each candle-power
an average duration is deducible from experience, so that two dependent
sets of data are obtained for the construction of the curve.

Curve, Load.
A characteristic curve of a dynamo, expressing the relation between its
voltage and the amount of excitation under a definite condition of
ampere load, at a constant speed. The ordinates represent voltage, the
abscissas ampere turns in the field, and the curves may be constructed
for a flow of 0, 50, 100, or .. , or any other number of amperes.

Fig. 123. LOAD CURVES.

Curve, Magnetization.
A characteristic curve of an electromagnet, indicating the relation of
magnetization to exciting current. Laying off on the axis of ordinates
the quantities of magnetism evoked, and the corresponding strengths of
the exciting current on the axis of abscissas, the curve can be plotted.
It first rises rapidly, indicating a rapid increase of magnetization,
but grows nearly horizontal as the iron becomes more saturated. The
effect due to the coils alone, or the effect produced in the absence of
iron is a straight line, because air does not change in permeability.

Curve of Distribution of Potential in Armature.
A characteristic curve indicating the distribution of potential
difference between adjoining sections of the commutator of an armature
in different positions all around it. The potential differences are
taken by a volt-meter or potential galvanometer, connection with the
armature being made by two small metal brushes, held at a distance apart
equal to the distance from centre to centre of two adjoining commutator
bars. The curve is laid out as if by polar co-ordinates extending around
the cross-section of the commutator, with the distances from the
commutator surface to the curve proportional to the potential
differences as determined by shifting the pair of brushes all around the

The above is S. P. Thompson's method. Another method of W. M. Mordey
involves the use of a pilot brush. (See Brush, Pilot.) Otherwise the
method is in general terms identical with the above.





Curve of Dynamo.
The characteristic curve of a dynamo. (See Curve, Characteristic.)

Curve of Sines.
An undulating curve representing wave motion. It is produced by
compounding a simple harmonic motion, or a two and fro motion like that
of an infinitely long pendulum with a rectilinear motion. Along a
horizontal line points may be laid off to represent equal periods of
time. Then on each point a perpendicular must be erected. The length of
each must be equal to the length of path traversed by the point up to
the expiration of each one of the given intervals of time. The abscissas
are proportional to the times and the ordinates to the sines of angles
proportional to the times. Thus if a circle be drawn upon the line and
divided into thirty-two parts of equal angular value, the sines of these
angles may be taken as the ordinates and the absolute distance or length
of arc of the angle will give the abscissas.

Synonyms--Sine Curve--Sinusoidal Curve--Harmonic Curve.



Curve of Saturation of the Magnetic Circuit.
A characteristic curve whose ordinates may represent the number of
magnetic lines of force induced in a magnetic circuit, and whose
abscissas may represent the ampere turns of excitation or other
representative of the inducing force.

Curve of Torque.
A characteristic curve showing the relations between torque, q. v., and
current in a dynamo or motor.

Curve, Permeability Temperature.
A characteristic curve expressing the changes in permeability of a
paramagnetic substance as the temperature changes. The degrees of
temperature may be abscissas, and the permeabilities corresponding
thereto ordinates of the curve.

Cut In. v.
To connect any electric appliance, mechanism or conductor, into a

Cut Out. v.
The reverse of to cut in; to remove from a circuit any conducting
device, and sometimes so arranged as to leave the circuit completed in
some other way.

Cut Out.
An appliance for removing any apparatus from an electric circuit, so
that no more current shall pass through such apparatus, and sometimes
providing means for closing the circuit so as to leave it complete after
the removal of the apparatus.


Cut Out, Automatic.
(a) A mechanism for automatically shunting an arc or other lamp when it
ceases to work properly. It is generally worked by an electro-magnet of
high resistance placed in parallel with the arc. If the arc grows too
long the magnet attracts its armature, thereby completing a shunt of
approximately the resistance of the arc, and which replaces it until the
carbons approach again to within a proper distance. Sometimes a strip or
wire of fusible metal is arranged in shunt with the arc. When the arc
lengthens the current through the wire increases, melts it and a spring
is released which acts to complete or close a shunt circuit of
approximately arc-resistance.

(b) See Safety Device--Safety Fuse.

(c) See below.

Cut-out, Magnetic.
A magnetic cut-out is essentially a coil of wire with attracted core or
armature. When the coil is not excited the core, by pressing down a
strip of metal or by some analogous arrangement, completes the circuit.
When the current exceeds a certain strength the core rises as it is
attracted and the circuit is opened.

Cut-out, Safety.
A block of porcelain or other base carrying a safety fuse, which melts
and breaks the circuit before the wire connected to it is dangerously

Synonyms--Fuse Block--Safety Catch--Safety Fuse.

Cut Out, Wedge.
A cut out operated by a wedge. The line terminals consist of a spring
bearing against a plate, the circuit being completed through their point
of contact. A plug or wedge composed of two metallic faces insulated
from each other is adapted to wedge the contact open. Terminals of a
loop circuit are connected to the faces of the wedge. Thus on sliding it
into place, the loop circuit is brought into series in the main circuit.

Synonym--Plug Cut Out--Spring Jack.

Cutting of Lines of Force.
A field of force is pictured as made up of lines of force; a conductor
swept through the field is pictured as cutting these lines. By so doing
it produces potential difference or electro-motive force in itself with
a current, if the conductor is part of a closed circuit.

Cycle of Alternation.
A full period of alternation of an alternating current. It begins
properly at the zero line, goes to a maximum value in one sense and
returns to zero, goes to maximum in the other sense and returns to zero.

Examination of the human bladder by the introduction of a special
incandescent electric lamp. The method is due to Hitze.


(a) A copper frame on which the wire in a galvanometer is sometimes
coiled, which acts to damp the oscillations of the needle.

(b) A tube of brass or copper placed between the primary and secondary
coils of an induction coil. It cuts off induction and diminishes the
current and potential of the secondary circuit. On pulling it out, the
latter increases. It is used on medical coils to adjust their strength
of action.

Preventing the indicator of an instrument from oscillating in virtue of
its own inertia or elasticity. In a galvanometer it is defined as
resistance to quick vibrations of the needle, in consequence of which it
is rapidly brought to rest when deflected (Ayrton). In dead-beat
galvanometers (see Galvanometer, Dead-Beat,) damping is desirable in
order to bring the needle to rest quickly; in ballistic galvanometers
(see Galvanometer, Ballistic,) damping is avoided in order to maintain
the principle of the instrument. Damping may be mechanical, the
frictional resistance of air to an air-vane, or of a liquid to an
immersed diaphragm or loosely fitting piston, being employed. A
dash-pot, q. v., is an example of the latter. It may be
electro-magnetic. A mass of metal near a swinging magnetic needle tends
by induced currents to arrest the oscillations thereof, and is used for
this purpose in dead-beat galvanometers. This is termed, sometimes,
magnetic friction. The essence of damping is to develop resistance to
movement in some ratio proportional to velocity, so that no resistance
is offered to the indicator slowly taking its true position. (See
Galvanometer, Dead-Beat.)

A cylinder and piston, the latter loosely fitting or perforated, or some
equivalent means being provided to permit movement. The cylinder may
contain a liquid such as glycerine, or air only. Thus the piston is
perfectly free to move, but any oscillations are damped (see Damping).
In some arc lamps the carbon holder is connected to a dash-pot to check
too sudden movements of the carbon. The attachment may be either to the
piston or to the cylinder. In the Brush lamp the top of the carbon
holder forms a cylinder containing glycerine, and in it a loosely
fitting piston works. This acts as a dash-pot.

Dead Beat. adj.
Reaching its reading quickly; applied to instruments having a moving
indicator, which normally would oscillate back and forth a number of
times before reaching its reading were it not prevented by damping. (See
Galvanometer, Aperiodic--Damping.)

Dead Earth.
A fault in a telegraph line which consists in the wire being thoroughly
grounded or connected to the earth.


Dead Point of an Alternator.
A two-phase alternator of the ordinary type connected as a motor to
another alternator cannot start itself, as it has dead points where the
relations and polarity of field and armature are such that there is no
torque or turning power.

In the winding of an armature, a given percentage of the turns, it may
be 80 per cent., more or less, is assumed to be active; the other 20 per
cent. or thereabouts, is called dead-turns. This portion represents the
wire on such portions of the armature as comes virtually outside of the
magnetic field. They are termed dead, as not concurring to the
production of electro-motive force.

Dead Wire.
(a) The percentage or portion of wire on a dynamo or motor armature that
does not concur in the production of electromotive force. The
dead-turns, q. v., of a drum armature or the inside wire in a Gramme
ring armature are dead wire.

(b) A disused and abandoned electric conductor, such as a telegraph

(c) A wire in use, but through which, at the time of speaking, no
current is passing.

Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period.
Amperage probably has something to do with it, although the total
quantity in coulombs may be very small. As applied to the execution of
criminals, the victim is seated in a chair and strapped thereto. One
electrode with wet padded surface is placed against his head or some
adjacent part. Another electrode is placed against some of the lower
parts, and a current from an alternating dynamo passed for 15 seconds or
more. The potential difference of the electrodes is given at 1,500 to
2,000 volts, but of course the maximum may be two or three times the
measured amount, owing to the character of the current.

The converse of recalescence, q. v. When a mass of steel is being heated
as it reaches the temperature of recalescence it suddenly absorbs a
large amount of heat, apparently growing cooler.

Prefix originally used in the metric system to signify one-tenth of, now
extended to general scientific units. Thus decimeter means one-tenth of
a meter; decigram, one-tenth of a gram.

Declination, Angle of.
The angle intercepted between the true meridian and the axis of a
magnetic needle at any place. The angle is measured to east or west,
starting from the true meridian as zero.


Declination of the Magnetic Needle.
The deviation of the magnetic needle from the plane of the earth's
meridian. It is also called the variation of the compass. (See Magnetic

The reduction of a compound substance into its constituents, as in
chemical analysis. The constituents may themselves be compounds or
proximate constituents, or may be elemental or ultimate constituents.

Decomposition, Electrolytic.
The decomposition or separation of a compound liquid into its
constituents by electrolysis. The liquid must be an electrolyte, q. v.,
and the decomposition proceeds subject to the laws of electrolysis, q.
v. See also Electrolytic Analysis.

When a suspension needle which has been disturbed is oscillating the
swings gradually decrease in amplitude if there is any damping, as there
always is. The decrement is the ratio of the amplitude of one
oscillation to the succeeding one. This ratio is the same for any
successive swings.

To cut off its supply of electric energy from an electric motor, or any
device absorbing and worked by electric energy.

The explosive or violent volatilizing and dissipating of a substance by
heat, violent oxidation and similar means. It may be applied among other
things to the destroying of a conductor by an intense current, or the
volatilization of any material by the electric arc.

Deflecting Field.
The field produced in a galvanometer by the current which is being
tested, and which field deflects the needle, such deflection being the
measure of the current strength.

In magnetism the movement out of the plane of the magnetic meridian of a
magnetic needle, due to disturbance by or attraction towards a mass of
iron or another magnet.

Deflection Method.
The method of electrical measurements in which the deflection of the
index of the measuring instrument is used as the measure of the current
or other element under examination. It is the opposite of and is to be
distinguished from the zero or null method, q. v. In the latter
conditions are established which make the index point to zero and from
the conditions necessary for this the measurement is deduced. The
Wheatstone Bridge, q. v., illustrates a zero method, the sine or the
tangent compass, illustrates a deflection method. The use of deflection
methods involves calibration, q. v., and the commercial measuring
instruments, such as ammeters and volt meters, which are frequently
calibrated galvanometers, are also examples of deflection instruments.


Degeneration, Reaction of.
The diminished sensibility to electro-therapeutic treatment exhibited by
the human system with continuance of the treatment in question. The
general lines of variation are stated in works on the subject.

Prefix originally used in the metric system to signify multiplying by
ten, as dekameter, ten meters, dekagram, ten grams; now extended to many
scientific terms.

De la Rive's Floating Battery.
A small galvanic couple, immersed in a little floating cell and
connected through a coil of wire immediately above them. When the
exciting battery solution is placed in the cell the whole, as it floats
in a larger vessel, turns until the coil lies at right angles to the
magnetic needle. Sometimes the two plates are thrust through a cork and
floated thus in a vessel of dilute sulphuric acid.

A magnet acts to attract or repel the coil in obedience to Ampére's
Theory, (See Magnetism, Ampere's Theory of.)

Delaurier's Solution.
A solution for batteries of the Bunsen and Grenet type. It is of the
following composition:
     Water,                2,000 parts;
  potassium bichromate,   184 parts;
  sulphuric acid,         428 parts.

Removal of magnetism from a paramagnetic substance. It is principally
used for watches which have become magnetized by exposure to the
magnetic field surrounding dynamos or motors.

The general principles of most methods are to rotate the object, as a
watch, in a strong field, and while it is rotating to gradually remove
it from the field, or to gradually reduce the intensity of the field
itself to zero. A conical coil of wire within which the field is
produced in which the watch is placed is sometimes used, the idea being
that the field within such a coil is strongest at its base. Such a coil
supplied by an alternating current is found effectual (J. J. Wright).

If a magnetized watch is made to turn rapidly at the end of a twisted
string and is gradually brought near to and withdrawn from the poles of
a powerful dynamo it may be considerably improved.

A hollow coil of wire connected with a pole changer and dip-battery has
been used. The battery creates a strong field within the coil. The watch
is placed there and the pole changer is worked so as to reverse the
polarity of the field very frequently. By the same action of the pole
changer the plates of the battery are gradually withdrawn from the
solution so as to gradually reduce the magnetic field to zero while
constantly reversing its polarity. (G. M. Hopkins.)

Steel may be demagnetized by jarring when held out of the magnetic
meridian, or by heating to redness.


Density, Electric Superficial.
The relative quantity of electricity residing as an electric charge upon
a unit area of surface. It may be positive or negative.

Synonyms--Density of Charge--Surface Density.

Dental Mallet, Electric.
A dentist's instrument for hammering the fillings as inserted into
teeth. It is a little hammer held in a suitable handle, and which is
made to strike a rapid succession of blows by electro-magnetic motor

(a) The removal of permanent magnetism. (See Demagnetization.)

(b) The prevention of the polarization of a galvanic cell. It is
effected in the Grove battery by the reduction of nitric acid; in the
Bunsen, by the reduction of chromic acid; in the Smee battery,
mechanically, by the platinum coated or rather platinized negative
plate. Other examples will be found under the description of various
cells and batteries. A fluid which depolarizes is termed a depolarizer
or depolarizing fluid or solution. (See Electropoion Fluid.)

Deposit, Electrolytic.
The metal or other substance precipitated by the action of a battery or
other current generator.

Derivation, Point of.
A point where a circuit branches or divides into two or more leads. The
separate branches then receive derived or partial currents.

Desk Push.
A press or push button, with small flush rim, for setting into the
woodwork of a desk.

A portable galvanometer, often of simple construction, used for rough or
approximate work.

Detector, Lineman's.
A portable galvanometer with a high and a low resistance actuating coil,
constructed for the use of linemen and telegraph constructors when in
the field, and actually putting up, repairing or testing lines.

Deviation, Quadrantal.
Deviation of the compass in iron or steel ships due to the magnetization
of horizontal beams by the earth's induction. The effect of this
deviation disappears when the ship is in the plane of the electric
meridian, or at right angles thereto; its name is taken from the fact
that a swing of the ship through a quadrant brings the needle from zero
deviation to a maximum and back to zero.


Deviation, Semicircular.
Deviation of the compass in iron or steel ships due to vertical
induction. (See Induction, Vertical.) The effect of this induction
disappears when the ship is in the electric meridian. Its name is
derived from the fact that a swing of the ship through half the circle
brings the needle from zero deviation to a maximum and back to zero.

Dextrotorsal. adj.
Wound in the direction or sense of a right-handed screw; the reverse of
sinistrotorsal, q. v.


Diacritical. adj.
(a) The number of ampere turns, q. v., required to bring an iron core to
one half its magnetic saturation, q. v., is termed the diacritical

(b) The diacritical point of magnetic saturation is proposed by Sylvanus
P. Thompson as a term for the coefficient of magnetic saturation which
gives a magnet core one-half its maximum magnetization.

Diagnosis, Electro.
A medical diagnosis of a patient's condition based on the action of
different parts of the body under electric excitement.

Diamagnetic. adj.
Possessing a negative coefficient of magnetic susceptibility; having
permeability inferior to that of air. Such substances placed between the
poles of a magnet are repelled; if in the form of bars, they tend to
turn so as to have their long axis at right angles to the line joining
the poles. The reason is that the lines of force always seek the easiest
path, and these bodies having higher reluctance than air, impede the
lines of force, and hence are as far as possible pushed out of the way.
The above is the simplest explanation of a not well understood set of
phenomena. According to Tyndall, "the diamagnetic force is a polar
force, the polarity of diamagnetic bodies being opposed to that of
paramagnetic ones under the same conditions of excitement." Bismuth is
the most strongly diamagnetic body known; phosphorus, antimony, zinc,
and many others are diamagnetic. (See Paramagnetic.)


An apparatus for use in chemical analysis for testing the purity of
substances by the time required for a charged surface to be discharged
through them to earth. It is the invention of Rousseau.

An electrometer is charged with a dry pile. One of its terminals is
connected with one surface of the solution or substance to be tested,
and the other with the other surface. The time of discharge gives the
index of the purity of the substance.

Diamagnetic Polarity.
Treating diamagnetism as due to a polar force, the polarity of a
diamagnetic body is the reverse of the polarity of iron or other
paramagnetic bodies. A bar-shaped diamagnetic body in a field of force
tends to place itself at right angles to the lines of force.

(a) The science or study of diamagnetic substances and phenomena.

(b) The magnetic property of a diamagnetic substance.

Diameter of Commutation.
The points on the commutator of a closed circuit ring--or
drum--armature, which the brushes touch, and whence they take the
current, mark the extremities of the diameter of commutation. Were it
not for the lag this would be the diameter at right angles to the line
connecting the centers of the opposite faces of the field. It is always
a little to one side of this position, being displaced in the direction
of rotation. In open circuit armatures the brushes are placed on the
diameter at right angles to this one, and sometimes the term diameter of
commutation is applied to it. All that has been said is on the
supposition that the armature divisions correspond not only in
connection but in position with those of the armature coils. Of course,
the commutator could be twisted so as to bring the diameter of
commutation into any position desired.

Diapason, Electric.
A tuning-fork or diapason kept in vibration by electricity. In general
principle the ends of the fork act as armatures for an electro-magnet,
and in their motion by a mercury cup or other form of contact they make
and break the circuit as they vibrate. Thus the magnet alternately
attracts and releases the leg, in exact harmony with its natural period
of vibration.

(a) In telephones and microphones a disc of iron thrown into motion by
sound waves or by electric impulses, according to whether it acts as the
diaphragm of a transmitter or receiver. It is generally a plate of
japanned iron such as used in making ferrotype photographs. (See
Telephone and Microphone.)

(b) A porous diaphragm is often used in electric decomposition cells and
in batteries. The porous cup represents the latter use.

[Transcriber's note: Japanned--covered with heavy black lacquer, like
enamel paint.]


A non-conductor; a substance, the different parts of which may, after an
electric disturbance, remain, without any process of readjustment, and
for an indefinite period of time, at potentials differing to any extent
(Daniell). There is no perfect dielectric. The term dielectric is
generally only used when an insulator acts to permit induction to take
place through it, like the glass of a Leyden jar.

Dielectric Constant.
The number or coefficient expressing the relative dielectric capacity of
a medium or substance. (See Capacity, Specific Inductive.)

Dielectric, Energy of.
In a condenser, the conducting coatings are merely to conduct the
current all over the surface they cover; the keeping the electricities
separated is the work of the dielectric, and represents potential energy
which appears in the discharge. The amount of energy is proportional to
the charge, and to the potential difference. As any electrified body
implies an opposite electrification somewhere, and a separating
dielectric, the existence of a condenser is always implied.

[Transcriber's note: The energy stored in a capacitor (condenser) is
(Q*Q)/2C = (Q*V)/2 = (C*V*V)/2
The energy is proportional to the voltage SQUARED or the charge SQUARED.]

Dielectric Polarization.
A term due to Faraday. It expresses what he conceived to be the
condition of a dielectric when its opposite faces are oppositely
electrified. The molecules are supposed to be arranged by the
electrification in a series of polar chains, possibly being originally
in themselves seats of opposite polarities, or having such imparted to
them by the electricities. The action is analogous to that of a magnet
pole on a mass of soft iron, or on a pile of iron filings.

Dielectric Strain.
The strain a solid dielectric is subjected to, when its opposite
surfaces are electrified. A Leyden jar dilates under the strain, and
when discharged gives a dull sound. The original condition is not
immediately recovered. Jarring, shaking, etc., assist the recovery from
strain. The cause of the strain is termed Electric Stress. (See Stress,
Electric.) This is identical with the phenomenon of residual charge.
(See Charge, Residual.) Each loss of charge is accompanied with a
proportional return of the dielectric towards its normal condition.

Dielectric Resistance.
The mechanical resistance a body offers to perforation or destruction by
the electric discharge.

Dielectric Strength.
The resistance to the disruptive discharge and depending on its
mechanical resistance largely or entirely. It is expressible in volts
per centimeter thickness. Dry air requires 40,000 volts per centimeter
for a discharge.


Differential Winding Working.
A method of working an electro-magnet intermittently, so as to avoid
sparking. The magnet is wound with two coils. One is connected straight
into the circuit, the other is connected in parallel therewith with a
switch inserted. The coils are so connected that when the switch is
closed the two are in opposition, the current going through them in
opposite senses. Thus one overcomes the effect of the other and the
magnet core shows no magnetism, provided the two coils are of equal
resistance and equal number of convolutions or turns.


A term properly applied to the varying current density found in
conductors of unequal cross sectional area. In electro-therapeutics it
is applied to the distribution of current as it passes through the human
body. Its density per cross-sectional area varies with the area and
with the other factors.

Diffusion Creep.
When electrodes of an active circuit are immersed in a solution of an
electrolyte, a current passes electrolytically if there is a sufficient
potential difference. The current passes through all parts of the
solution, spreading out of the direct prism connecting or defined by the
electrodes. To this portion of the current the above term is applied. If
the electrodes are small enough in proportion to the distance between
them the current transmission or creep outside of the line becomes the
principal conveyor of the current so that the resistance remains the
same for all distances.

Dimensions and Theory of Dimensions.
The expression of the unitary value of a physical quantity in one or
more of the units of length (L), time (T) and mass (M) is termed the
dimensions of such quantity. Thus the dimension or dimensions of a
distance is simply L; of an angle, expressible by dividing the arc by
the radius is L/L; of a velocity, expressible by distance divided by
time--L/T; of acceleration, which is velocity acquired in a unit of
time, and is therefore expressible by velocity divided by time--L/T/T or
L/T2; of momentum, which is the product of mass into velocity--M*L/T; of
kinetic energy taken as the product of mass into the square of
velocity--M*(L2/T2); of potential energy taken as the product of mass
into acceleration into space-M*(L/T2)*L reducing to M*(L2/T2). The
theory is based on three fundamental units and embraces all electric
quantities. The simple units generally taken are the gram, centimeter
and second and the dimensions of the fundamental compound units are
expressed in terms of these three, forming the centimeter-gram-second or
C. G. S. system of units. Unless otherwise expressed or implied the
letters L, M and T, may be taken to indicate centimeter, gram and second
respectively. It is obvious that very complicated expressions of
dimensions may be built up, and that a mathematical expression of
unnamed quantities may be arrived at. Dimensions in their application by
these symbols are subject to the laws of algebra. They were invented by
Fourier and were brought into prominence by J. Clerk Maxwell. Another
excellent definition reads as follows: "By the dimensions of a physical
quantity we mean the quantities and powers of quantities, involved in
the measurement of it." (W. T. A. Emtage.)


An adjustable choking coil used for regulating the intensity of electric
incandescent lights. Some operate by the introduction and withdrawal of
an iron core as described for the choking coil (see Coil, Choking),
others by a damper of copper, often a copper ring surrounding the coil
and which by moving on or off the coil changes the potential of the
secondary circuit.

Dip of Magnetic Needle.
The inclination of the magnetic needle. (See Elements, Magnetic.)

(a) Acid or other cleaning processes applied by dipping metals in
cleaning or pickling solutions before plating in the electroplater's

(b) Plating by dipping applies to electroplating without a battery by
simple immersion. Copper is deposited on iron from a solution of copper
sulphate in this way.

Synonym--Simple Immersion.

Dipping Needle.
A magnet mounted in horizontal bearings at its centre of gravity. Placed
in the magnetic meridian it takes the direction of the magnetic lines of
force of the earth at that point. It is acted on by the vertical
component of the earth's magnetism, as it has no freedom of horizontal
movement. (See Magnetic Elements, and Compass, Inclination.)

Directing Magnet.
In a reflecting galvanometer the magnet used for controlling the
magnetic needle by establishing a field. It is mounted on the spindle of
the instrument above the coil and needle.

Synonym--Controlling Magnet.


(a) The direction of an electric current is assumed to be from a
positively charged electrode or terminal to a negatively charged one in
the outer circuit. (See Current.)

(b) The direction of magnetic and electro-magnetic lines of force is
assumed to be from north to south pole of a magnet in the outer circuit.
It is sometimes called the positive direction. Their general course is
shown in the cuts diagrammatically. The circles indicate a compass used
in tracing their course. The magnetic needle tends to place itself in
the direction of or tangential to the lines of force passing nearest it.

(c) The direction of electrostatic lines of force is assumed to be out
of a positively charged and to a negatively charged surface.




Directive Power.
In magnetism the power of maintaining itself in the plane of the
magnetic meridian, possessed by the magnetic needle.

Discharge, Brush.
The static discharge of electricity into or through the air may be of
the brush or spark form. The brush indicates the escape of electricity
in continuous flow; the spark indicates discontinuity. The conditions
necessary to the production of one or the other refer to the nature of
the conductor, and of other conductors in its vicinity and to the
electro-motive force or potential difference; small alterations may
transform one into the other. The brush resembles a luminous core whose
apex touches the conductor. It is accompanied by a slight hissing noise.
Its luminosity is very feeble. The negative conductor gives a smaller
brush than that of the positive conductor and discharges it more
readily. When electricity issues from a conductor, remote from an
oppositely excited one, it gives an absolutely silent discharge, showing
at the point of escape a pale blue luminosity called electric glow, or
if it escapes from points it shows a star-like centre of light. It can
be seen in the dark by placing a point on the excited conductor of a
static-electric machine.

Synonyms--Silent Discharge--Glow Discharge.

Discharge, Conductive.
A discharge of a static charge by conduction through a conductor.

Discharge, Convective.
The discharge of static electricity from an excited conductor through
air or rarefied gas; it is also called the quiet or silent discharge.
The luminous effect in air or gas at atmospheric pressures takes the
form of a little brush from a small positive electrode; the negative
shows a star. The phenomena of Gassiot's cascade, the philosopher's egg
and Geissler tubes, all of which may be referred to, are instances of
convective discharge.

Discharge, Dead Beat.
A discharge that is not oscillatory in character.

Discharge, Disruptive.
A discharge of a static charge through a dielectric. It involves
mechanical perforation of the dielectric, and hence the mere mechanical
strength of the latter has much to do with preventing it. A disruptive
discharge is often oscillatory in character; this is always the case
with the discharge of a Leyden jar.


Discharge, Duration of.
The problem of determining this factor has been attacked by various
observers. Wheatstone with his revolving mirror found it to be 1/24000
second. Fedderson, by interposing resistance, prolonged it to 14/10000
and again to 138/10000 second. Lucas & Cazin made it from 26 to 47
millionths of a second. All these experiments were performed with Leyden

Discharge, Impulsive.
A disruptive discharge produced between conductors by suddenly produced
potential differences. The self-induction of the conductor plays an
especially important part in discharges thus produced.

Discharge, Lateral.
(a) A lightning discharge, which sometimes takes place between a
lightning rod and the building on which it is.

(b) In the discharge of a Leyden jar or condenser the discharge which
takes the alternative path, q. v.

Discharge, Oscillatory.
The sudden or disruptive discharge of a static condenser, such as a
Leyden jar, or of many other charged conductors, is oscillatory in
character. The direction of the currents rapidly changes, so that the
discharge is really an alternating current of excessively short total
duration. The discharge sends electro-magnetic waves through the ether,
which are exactly analogous to those of light but of too long period to
affect the eye.

Synonym--Surging Discharge.

[Transcriber's note: Marconi's transmission across the English channel
occurs in 1897, five years after the publication of this book.]


An apparatus for discharging Leyden jars. It consists of a conductor
terminating in balls, and either jointed like a tongs or bent with a
spring-action, so that the balls can be set at distances adapted to
different sized jars. It has an insulating handle or a pair of such. In
use one ball is brought near to the coating and the other to the spindle
ball of the jar. When nearly or quite in contact the jar discharges.

Synonyms--Discharging Rod--Discharging Tongs.


Discharger, Universal.
An apparatus for exposing substances to the static discharge spark. It
consists of a base with three insulating posts. The central post carries
an ivory table to support the object. The two side posts carry
conducting rods, terminating in metal balls, and mounted with universal
joints. A violent shock can be given to any object placed on the table.

Synonym--Henley's Universal Discharger.

Discharge, Silent.
This term is sometimes applied to the glow or brush discharge and
sometimes to the condition of electric effluvium. (See Discharge,
Brush--Effluvium, Electric.)

Discharge, Spark.
The discontinuous discharge of high tension electricity through a
dielectric or into the air produces electric sparks. These are quite
strongly luminous, of branching sinuous shape, and in long sparks the
luminosity varies in different parts of the same spark. A sharp noise
accompanies each spark. High density of charge is requisite for the
formation of long sparks.

The separation of two parts of, or opening a circuit, as by turning a
switch, unscrewing a binding screw, or the like. The term is sometimes
used to indicate a class of faults in telegraph circuits. Disconnections
may be total, partial or intermittent, and due to many causes, such as
open or partially replaced switches, oxidized or dirty contact points,
or loose joints.

Displacement, Electric.
A conception of the action of charging a dielectric. The charge is all
on the surface. This fact being granted, the theory of displacement
holds that charging a body is the displacing of electricity, forcing it
from the interior on to the surface, or vice versa, producing a positive
or negative charge by displacement of electricity. While displacement is
taking place in a dielectric there is assumed to be a movement or
current of electricity called a displacement current.

Disruptive Tension.
When the surface of a body is electrified, it tends to expand, all
portions of the surface repelling each other. The film of air
surrounding such a body is electrified too, and is subjected to a
disruptive tension, varying in intensity with the square of the density.

Dissimulated Electricity.
The electricity of a bound charge. (See Charge, Bound.)

The separation of a chemical compound into its elements by a
sufficiently high degree of heat. All compounds are susceptible of
dissociation, so that it follows that combustion is impossible at high


Distance, Critical, of Alternative Path.
The length of air gap in an alternative path whose resistance joined to
the impedance of the rest of the conductors of the path just balances
the impedance of the other path.

Distance, Sparking.
The distance between electrodes, which a spark from a given Leyden jar
or other source will pass across.

Synonym--Explosive Distance.

The evaporation of a liquid by heat, and sometimes in a vacuum, followed
by condensation of the vapors, which distil or drop from the end of the
condenser. It is claimed that the process is accelerated by the liquid
being electrified.

Distributing Box.
In an electric conduit system, a small iron box provided for giving
access to the cable for the purpose of making house and minor

Synonym--Hand Hole.

Distributing Switches.
Switch systems for enabling different dynamos to supply different lines
of a system as required. Spring jacks, q. v., are used for the lines,
and plug switches for the dynamo leads. Thus, dynamos can be thrown in
or out as desired, without putting out the lights.

Distribution of Electric Energy, Systems of.
The systems of electric current distribution from central stations or
from private generating plants, mechanical or battery, the latter
primary or secondary. They include in general the alternating current
system and direct current systems. Again, these may be subdivided into
series and multiple arc, multiple-series and series-multiple
distribution, and the three, four, or five wire system may be applied to
multiple arc or multiple series systems. (See Alternating
Current--Current System--Multiple Arc--Multiple Series--Series
Multiple--Three Wire System.)

Door Opener, Electric.
An apparatus for opening a door by pushing back the latch. A spring then
draws the door open, and it is closed against the force of the spring by
the person entering. Electro-magnetic mechanism actuates the latch, and
is operated by a switch or press-button. Thus a person on the upper
floor can open the hall door without descending.

Dosage, Galvanic.
In electro-therapeutics the amount of electric current or discharge, and
duration of treatment given to patients.

Double Carbon Arc Lamp.
An arc lamp designed to burn all night, usually constructed with two
parallel sets of carbons, one set replacing the other automatically, the
current being switched from the burnt out pair to the other by the
action of the mechanism of the lamp.


Double Fluid Theory.
A theory of electricity. Electricity is conveniently treated as a fluid
or fluids. According to the double fluid hypothesis negative electricity
is due to a preponderance of negative fluid and vice versa. Like fluid
repels like, and unlike attracts unlike; either fluid is attracted by
matter; the presence in a body of one or the other induces
electrification; united in equal proportions they neutralize each other,
and friction, chemical decomposition and other causes effect their
separation. The hypothesis, while convenient, is overshadowed by the
certainty that electricity is not really a fluid at all. (See Single
Fluid Theory--Fluid, Electric.)

Synonym--Symmer's Theory.

[Transcriber's note: Current is the motion of negative electrons in a
conductor or plasma. Unequal distribution of electrons is static
electricity. The relatively immobile nuclei of atoms are positive when
one or more of its electrons is absent and accounts for part of the
current in electrolysis and plasmas.]

Double Fluid Voltaic Cell.
A cell in which two fluids are used, one generally as depolarizer
surrounding the negative plate, the other as excitant surrounding the
positive plate. A porous diaphragm or difference in specific gravities
is used to keep the solutions separate and yet permit the essential
electrolytic diffusion. Grove's Cell, Bunsen's Cell, and Daniell's Cell,
all of which may be referred to, are of this type, as are many others.

Double Wedge.
A plug for use with a spring-jack. It has connection strips at its end
and another pair a little distance back therefrom, so that it can make
two loop connections at once.

Synonym--Double Plug.

A continuously acting electrophorous, q.v.; an early predecessor of the
modern electric machines. It is now no longer used.

D. P.
Abbreviation for Potential Difference.

The pull exercised by a magnetic field upon a conductor moving through
it or upon the motion of an armature in it.

Dreh-strom. (German)
Rotatory currents; a system of currents alternating in periodic
succession of phases and producing a rotatory field. (See Field,
Rotatory--Multiphase Currents.)

Drill Electric.
A drill for metals or rock worked by an electro-magnetic motor. For
metals a rotary motion, for rocks a reciprocating or percussion action
is imparted. It is used by shipbuilders for drilling holes in plates
which are in place in ships, as its flexible conductors enable it to be
placed anywhere. For rock-drilling a solenoid type of construction is
adopted, producing rapid percussion.


Drip Loop.
A looping downward of wires entering a building, so that rain water, as
it runs along the wire, will drip from the lowest part of the loop
instead of following the wire into or against the side of the building.

Driving Horns.
Projections on the periphery of an armature of a dynamo for holding the
winding in place and preventing its displacement. Various arrangements
have been adopted. They are sometimes wedges or pins and are sometimes
driven into spaces left in the drum core. The toothed disc armature
cores make up an armature in which the ridges formed by the teeth form
practically driving horns.

Dronier's Salt.
A substance for solution for use in bichromate batteries. It is a
mixture of one-third potassium bichromate and two-thirds potassium
bisulphate. It is dissolved in water to make the exciting fluid.

Drop, Automatic.
A switch or circuit breaker, operating to close a circuit by dropping
under the influence of gravity. It is held up by a latch, the circuit
remaining open, until the latch is released by a current passing through
an electro-magnet. This attracting an armature lets the drop fall. As it
falls it closes a local or second circuit, and thus may keep a bell
ringing until it is replaced by hand. It is used in burglar alarms, its
function being to keep a bell ringing even though the windows or door by
which entrance was made is reclosed.



Drum, Electric.
A drum with a mechanism within for striking the head with a hammer or
some equivalent method so as to be used as a piece of magical apparatus.
In the one shown in the cut a sort of telephone action is used to
produce the sound, the electro-magnet D and armature being quite
screened from observation through the hole. (See Fig. 133) A ring, C,
shown in Fig. 133, with two terminals, the latter shown by the unshaded
portions a a, and a suspending hook E, also with two terminals, and two
suspending conductors A, B, carry the current to the magnet. A sudden
opening or closing of the circuit produces a sound.

Dub's Laws.
1. The magnetism excited at any transverse section of a magnet is
proportional to the square root of the distance between the given
section and the end.

2. The free magnetism at any given transverse section of a magnet is
proportional to the difference between the square root of half the
length of the magnet and the square root of the distance between the
given section and the nearest end.

The tube or compartment in an electric subway for the reception of a
cable. (See Conduit, Electric Subway.)

A chemical term; an element which in combination replaces two monovalent
elements; one which has two bonds or is bivalent.

Dyeing, Electric.
The producing mordanting or other dyeing effects on goods in dyeing by
the passage of an electric current.

Dynamic Electricity.
Electricity of relatively low potential and large quantity; current
electricity as distinguished from static electricity; electricity in


Dynamo, Alternating Current.
A dynamo-electric machine for producing an alternating current; an
alternator. They are classified by S. P. Thompson into three classes--I.
Those with stationary field-magnet and rotating armature. II. Those with
rotating field magnet and stationary armature. III. Those with both
field magnet part and armature part stationary, the amount of magnetic
induction from the latter through the former being caused to vary or
alternate in direction by the revolution of appropriate pieces of iron,
called inductors. Another division rests on whether they give one simple
alternating current, a two phase current, or whether they give multi
phase currents. (See Current, Alternating--Currents, Multiphase.)

A great many kinds of alternators have been constructed. Only an outline
of the general theory can be given here. They are generally multipolar,
with north and south poles alternating around the field. The armature
coils, equal in number in simple current machines, to the poles, are
wound in opposite senses, so that the current shall be in one direction,
though in opposite senses, in all of them at anyone time. As the
armature rotates the coils are all approaching their poles at one time
and a current in one sense is induced in every second coil, and one in
the other sense in the other coils. They are all in continuous circuit
with two open terminals, each connected to its own insulated connecting
ring on the shaft. As the coils pass the poles and begin to recede from
them the direction changes, and the current goes in the other direction
until the next poles are reached and passed. Thus there are as many
changes of direction of current per rotation as there are coils in the
armature or poles in the field.



The field-magnets whose windings may be in series are often excited by a
separate direct current generation. Some are self-exciting, one or more
of the armature coils being separated from the rest, and connected to a
special commutator, which rectifies its current.

By properly spacing the coils with respect to the poles of the field,
and connecting each set of coils by itself to separate connecting rings,
several currents can be taken from the same machine, which currents
shall have a constant difference in phase. It would seem at first sight
that the same result could be attained by using as many separate
alternators as there were currents to be produced. But it would be
almost impossible to preserve the exact relation of currents and current
phase where each was produced by its own machine. The currents would
overrun each other or would lag behind. In a single machine with
separate sets of coils the relation is fixed and invariable.


Dynamo, Alternating Current, Regulation of.
Transformers, converters, or induction coils are used to regulate
alternating current dynamos, somewhat as compound winding is applied in
the case of direct-current dynamos. The arrangement consists in
connecting the primary of an induction coil or transformer into the
external circuit with its secondary connected to the field circuit. Thus
the transformer conveys current to the field picked up from the main
circuit, and represents to some extent the shunt of a direct-current

Dynamo, Commercial Efficiency of.
The coefficient, q. v., obtained by dividing the mechanically useful or
available work of a dynamo by the mechanical energy absorbed by it. This
only includes the energy available in the outer circuit, for doing
useful work.



Dynamo. Compound.
A compound wound dynamo; one which has two coils on its field magnet;
one winding is in series with the external circuit and armature; the
other winding is in parallel with the armature winding, or else with the
armature winding and field winding, both in series. (See Winding, Long
Shunt--Winding, Short Shunt.)

Such a dynamo is, to a certain extent, self-regulating, the two coils
counteracting each other, and bringing about a more regular action for
varying currents than that of the ordinary shunt or series dynamo.

The extent of the regulation of such a machine depends on the
proportions given its different parts. However good the self-regulating
may be in a compound wound machine, it can only be perfect at one
particular speed.

To illustrate the principle on which the approximate regulation is
obtained the characteristic curve diagram may be consulted.


One curve is the curve of a series winding, the other that of a shunt
winding, and shows the variation of voltage in each with resistance in
the external or working circuit. The variation is opposite in each case.
It is evident that the two windings could be so proportioned on a
compound machine that the resultant of the two curves would be a
straight line. This regulation would then be perfect and automatic, but
only for the one speed.


Dynamo, Direct Current.
A dynamo giving a current of unvarying direction, as distinguished from
an alternator or alternating current dynamo.

Dynamo, Disc.
A dynamo with a disc armature, such as Pacinotti's disc, q. v. (See also
Disc, Armature.) The field magnets are disposed so that the disc rotates
close to their poles, and the poles face or are opposite to the side or
sides of the disc. The active leads of wire are those situated on the
face or faces of the disc.


Dynamo-electric Machine.
A machine driven by power, generally steam power, and converting the
mechanical energy expended on driving it into electrical energy of the
current form. The parts of the ordinary dynamo may be summarized as
follows: First, A circuit as complete as possible of iron. Such circuit
is composed partly of the cores of an electro-magnet or of several
electro-magnets, and partly of the cylindrical or ring-shaped core of an
armature which fits as closely as practicable between the magnet ends or
poles which are shaped so as to partly embrace it. Second, of coils of
insulated wire wound upon the field-magnet cores. When these coils are
excited the field-magnets develop polarity and the circuit just spoken
of becomes a magnetic circuit, interrupted only by the air gaps between
the poles and armatures. Thirdly, of coils of insulated wire upon the
armature core. These coils when rotated in the magnetic field cut
magnetic lines of force and develop electro-motive force.


Fourthly, of collecting mechanism, the commutator in direct current
dynamos, attached to the armature shaft and rotating with it. This
consists of insulated rings, or segments of rings to which the wire
coils of the armature are connected, and on which two springs of copper
or plates of carbon or some other conductor presses. The electro-motive
force developed by the cutting of lines of force, by the wires of the
armature, shows itself as potential difference between the two springs.
If the ends of a conductor are attached, one to each of these brushes,
the potential difference will establish a current through the wire. By
using properly divided and connected segments on the commutator the
potential difference and consequent direction of the current may be kept
always in the same sense or direction. It is now clear that the external
wire may be connected with the windings of the field-magnet. In such
case the excitement of the field-magnets is derived from the armature
and the machine is self-excited and entirely self-contained.

The above is a general description of a dynamo. Sometimes the coils of
the field-magnets are not connected with the armature, but derive their
current from an outside source. Such are termed separately excited

Some general features of dynamo generators may be seen in the
definitions under this head and elsewhere. The general conception is to
cut lines of force with a conductor and thus generate electromotive
force, or in some way to change the number of lines of force within a
loop or circuit with the same effect.

Dynamo, Electroplating.
A dynamo designed for low potential and high current intensity. They are
wound for low resistance, frequently several wires being used in
parallel, or ribbon, bar or rectangular conductors being employed. They
are of the direct current type. They should be shunt wound or they are
liable to reverse. They are sometimes provided with resistance in the
shunt, which is changed as desired to alter the electro-motive force.

Dynamo, Equalizing.
A combination for three and five-wire systems. A number of armatures or
of windings on the same shaft are connected across the leads. If the
potential drops at any pair of mains, the armature will begin to be
driven by the other mains, acting to an extent as an element of a motor,
and will raise the potential in the first pair.

Dynamo, Far Leading.
A motor dynamo, used to compensate the drop of potential in long mains.
Into the mains at a distant point a series motor is connected, driving a
dynamo placed in shunt across the mains. The dynamo thus driven raises
the potential difference between the two mains.


A printing telegraph in which the message is printed at both
transmitting and receiving ends.

Dynamo, Inductor.
A generator in which the armature or current-generating windings are all
comprised upon the poles of the field magnets. Masses of iron, which
should be laminated and are the inductors, are carried past the field
magnet poles concentrating in their passage the lines of force, thus
inducing currents in the coils. In one construction shown in the cut the
field magnets a, a .. are U shaped and are arranged in a circle, their
poles pointing inwards. A single exciting coil c, c ... is wound around
the circle in the bend of the V-shaped segments. The poles carry the
armature coils e, e ... The laminated inductors i, i ... are mounted on
a shaft S, by spiders h, to be rotated inside the circle of magnets,
thus generating an alternating current.

Synonym--Inductor Generator.


Dynamo, Interior Pole.
A dynamo with a ring armature, with field magnet pole pieces which
extend within the ring.


Dynamo, Iron Clad.
A dynamo in which the iron of the field magnet is of such shape as to
enclose the field magnet coils as well as the armature.

A device or apparatus for measuring force applied, or rate of
expenditure of energy by, or work done in a given time by a machine. A
common spring balance can be used as a force dynamometer, viz: to
determine how hard a man is pulling and the like. The steam engine
indicator represents an energy-dynamometer of the graphic type, the
instrument marking an area whence, with the aid of the fixed factors of
the engine, the work done may be determined. Prony's Brake, q. v., is a
type of the friction dynamometer, also of the energy type. In the latter
type during the experiment the whole power must be turned on or be
expended on the dynamometer.

Dynamo, Motor.
A motor dynamo is a machine for (a) converting a continuous current at
any voltage to a continuous current of different strength at a different
voltage or for (b) transforming a continuous current into an alternating
one, and vice versa.

For the first type see Transformer, Continuous Current; for the second
type see Transformer, Alternating Current.

Dynamo, Multipolar.
A dynamo having a number of field magnet poles, not merely a single
north and a single south pole. The field magnet is sometimes of a
generally circular shape with the poles arranged radially within it, the
armature revolving between the ends.

Dynamo, Non-polar.
A name given by Prof. George Forbes to a dynamo invented by him. In it a
cylinder of iron rotates within a perfectly self-contained iron-clad
field magnet. The current is taken off by brushes bearing near the
periphery, at two extremities of a diameter. A machine with a disc 18
inches in diameter was said to give 3,117 amperes, with 5.8 volts E. M.
F. running at 1,500 revolutions per second. The E. M. F. of such
machines varies with the square of the diameter of the disc or cylinder.

Dynamo, Open Coil.
A dynamo the windings of whose armatures may be grouped in coils, which
are not connected in series, but which have independent terminals. These
terminals are separate divisions of the commutator and so spaced that
the collecting brushes touch each pair belonging to the same coil
simultaneously. As the brushes come in contact with the sections forming
the terminals they take current from the coil in question. This coil is
next succeeded by another one, and so on according to the number of
coils employed.

Dynamo, Ring.
A dynamo the base of whose field magnets is a ring in general shape, or
perhaps an octagon, and with poles projecting inwardly therefrom.


Dynamo, Coupling of.
Dynamos can be coupled exactly like batteries and with about the same
general results. An instance of series coupling would be given by the
dynamos in the three wire system when no current is passing through the
neutral wire, and when the lamps on each side of it are lighted in equal

Dynamo, Self-exciting.
A dynamo which excites its own field. The majority of dynamos are of
this construction. Others, especially alternating current machines, are
separately excited, the field magnets being supplied with current from a
separate dynamo or current generator.

Dynamo, Separate Circuit.
A dynamo in which the field magnet coils are entirely disconnected from
the main circuit, and in which current for the field is supplied by
special coils carried for the purpose by the same armature, or by a
special one, in either case a special commutator being provided to
collect the current.

Dynamo, Separately Excited.
A dynamo whose field magnets are excited by a separate current
generator, such as a dynamo or even a battery. Alternating current
dynamos are often of this construction. Direct current dynamos are not
generally so. The term is the opposite of self-exciting.


Dynamo, Series.
A dynamo whose armature, field winding, and external circuit are all in

In such a dynamo short circuiting or lowering the resistance of the
external circuit strengthens the field, increases the electro-motive
force and current strength and may injure the winding by heating the
wire, and melting the insulation.


Dynamo, Shunt.
A dynamo whose field is wound in shunt with the external circuit. Two
leads are taken from the brushes; one goes around the field magnets to
excite them; the other is the external circuit.

In such a dynamo the lowering of resistance on the outer circuit takes
current from the field and lowers the electro-motive force of the
machine. Short circuiting has no heating effect.

Fig. 141.   SHUNT DYNAMO.

Dynamo, Single Coil.
A dynamo whose field magnet is excited by a single coil. Several such
have been constructed, with different shapes of field magnet cores, in
order to obtain a proper distribution of poles.

Dynamo, Tuning Fork.
A dynamo in which the inductive or armature coils were carried at the
ends of the prongs of a gigantic tuning fork, and were there maintained
in vibration opposite the field magnets. It was invented by T. A.
Edison, but never was used.

Dynamo, Uni-polar.
A dynamo in which the rotation of a conductor effects a continuous
increase in the number of lines cut, by the device of arranging one part
of the conductor to slide on or around the magnet. (S. P. Thomson.)
Faraday's disc is the earliest machine of this type.


The C. G. S. or fundamental unit of force. It is the force which can
impart an acceleration of one centimeter per second to a mass of one
gram in one second. It is equal to about 1/981 the weight of a gram,
this weight varying with the latitude.

(a) The earth is arbitrarily taken as of zero electrostatic potential.
Surfaces in such condition that their potential is unchanged when
connected to the earth are said to be of zero potential. All other
surfaces are discharged when connected to the earth, whose potential,
for the purposes of man at least, never changes.

(b) As a magnetic field of force the intensity of the earth's field is
about one-half a line of force per square centimeter.

(c) The accidental grounding of a telegraph line is termed an earth, as
a dead, total, partial, or intermittent earth, describing the extent and
character of the trouble.

[Transcriber's note: Fallen power lines can produce voltage gradients on
the earth's surface that make walking in the area dangerous, as in
hundreds of volts per foot. Lightning may be associated with substantial
changes in the static ground potential.]

Earth, Dead.
A fault, when a telegraph or other conductor is fully connected to earth
or grounded at some intermediate point.

Synonyms--Solid Earth--Total Earth.

Earth, Partial.
A fault, when a telegraph or other conductor is imperfectly connected to
earth or grounded at some intermediate point.

Earth Plate.
A plate buried in the earth to receive the ends of telegraph lines or
other circuits to give a ground, q. v. A copper plate is often used. A
connection to a water or gas main gives an excellent ground, far better
than any plate. When the plate oxidizes it is apt to introduce

Earth Return.
The grounding of a wire of a circuit at both ends gives the circuit an
earth return.

Earth, Swinging.
A fault, when a telegraph or other conductor makes intermittent
connection with the earth. It is generally attributable to wind action
swinging the wire, whence the name.

Hard vulcanized India rubber, black in color. Specific resistance in
ohms per cubic centimeter at 46º C. (115º F.): 34E15 (Ayrton); specific
inductive capacity, (air = 1): 2.56 (Wüllner); 2.76 (Schiller); 3.15
(Boltzmann). It is used in electrical apparatus for supporting members
such as pillars, and is an excellent material for frictional generation
of potential. Its black color gives it its name, and is sometimes made a
point of distinction from Vulcanite, q. v.


Economic Coefficient.
The coefficient of electric efficiency. (See Efficiency, Electric.)

Edison Effect.
A continuous discharge resulting in a true current which takes place
between a terminal of an incandescent lamp filament and a plate placed
near it. The lamp must be run at a definitely high voltage to obtain it.

An abbreviation for Edison-Swan; the trade name of the incandescent lamp
used in Great Britain, and of other incandescent system apparatus.


Eel, Electric (Gymnotus Electricus).
An eel capable of effecting the discharge of very high potential
electricity, giving painful or dangerous shocks. Its habitat is the
fresh water, in South America. Faraday investigated it and estimated its
shock as equal to that from fifteen Leyden jars, each of 1.66 square
feet of coating. (See Animal Electricity and Ray, Electric.)

Effect, Counter-inductive.
A counter-electro-motive force due to induction, and opposing a current.

The relation of work done to energy absorbed. A theoretically perfect
machine would have the maximum efficiency in which the two qualities
named would be equal to each other. Expressed by a coefficient, q. v.,
the efficiency in such case would be equal to 1. If a machine produced
but half the work represented by the energy it absorbed, the rest
disappearing in wasteful expenditure, in heating the bearings, in
overcoming the resistance of the air and in other ways, its efficiency
would be expressed by the coefficient 1/2 or .5, or if one hundred was
the basis, by fifty per centum. There are a number of kinds of
efficiencies of an electric generator which are given below.

Efficiency, Commercial.
Practical efficiency of a machine, obtained by dividing the available
output of work or energy of a machine by the energy absorbed by the same
machine. Thus in a dynamo part of the energy is usefully expended in
exciting the field magnet, but this energy is not available for use in
the outer circuit, is not a part of the output, and is not part of the

If M represents the energy absorbed, and W the useful or available
energy, the coefficient of commercial efficiency is equal to W/M. M is
made up of available, unavailable and wasted (by Foucault currents,
etc.,) energy. Calling available energy W, unavailable but utilized
energy w, and wasted energy m, the expression for the coefficient of
commercial efficiency becomes

  W / ( W + w + m )
  when M = W + w + m

Synonym--Net efficiency.


Efficiency, Electrical.
In a dynamo or generator the relation of total electric energy produced,
both wasted and useful or available to the useful or available
electrical energy. If we call W the useful electric and w the wasted
electric energy, the coefficient of electrical efficiency is equal to

  W / ( W + w )

Synonyms--Intrinsic Efficiency--Economic Coefficient--Coefficient of
Electrical Efficiency.

Efficiency of Conversion.
In a dynamo or generator the relation of energy absorbed to total
electric energy produced. Part of the electric energy is expended in
producing the field and in other ways. Thus a generator with high
efficiency of conversion may be a very poor one, owing to the
unavailable electric energy which it produces. The coefficient of
Efficiency of Conversion is obtained by dividing the total electric
energy produced by the energy absorbed in working the dynamo. If M
represents the energy absorbed, or work done in driving the dynamo or
generator, W the useful electric, and w the wasted electrical energy,
then the coefficient of efficiency of conversion is equal to

(W + w ) / M

In the quantity M are included besides available (W) and unavailable (w)
electric energy, the totally wasted energy due to Foucault currents,
etc., calling the latter m, the above formula may be given

( W+ w ) / (W + w + m )

This coefficient may refer to the action of a converter, q. v., in the
alternating system. Synonym--Gross Efficiency.

Efficiency of Secondary Battery, Quantity.
The coefficient obtained by dividing the ampere-hours obtainable from a
secondary battery by the ampere hours required to charge it.

Efficiency of Secondary Battery, Real.
The coefficient obtained by dividing the energy obtainable from a
secondary battery by the energy absorbed in charging it. The energy is
conveniently taken in watt-hours and includes the consideration of the
spurious voltage. (See Battery, Secondary.)


The appearance of a dry salt upon the walls of a vessel containing a
solution above the normal water-line from evaporation of a liquid. It
appears in battery jars and in battery carbons, in the latter
interfering with the electrical connections, and oxidizing or rusting
them. (See Creeping.)

Effluvium, Electric.
When a gas is made to occupy the position of dielectric between two
oppositely electrified surfaces a peculiar strain or condition of the
dielectric is produced, which promotes chemical change. The condition is
termed electrical effluvium or the silent discharge. By an apparatus
specially constructed to utilize the condition large amounts of ozone
are produced.

Synonym--Silent Discharge.

Elastic Curve.
A crude expression for a curve without projections or sudden
sinuosities; such a curve as can be obtained by bending an elastic strip
of wood.

An obsolete name for a key, switch or pole changer of any kind.

Elasticity, Electric.
The phenomenon of the dielectric is described under this term. When a
potential difference is established between two parts of the dielectric,
a flow of electricity displacement current starts through the
dielectric, which current is due to the electric stress, but is
instantly arrested by what has been termed the electric elasticity of
the dielectric. This is expressed by
  ( electric stress ) / ( electric strain )
and in any substance is inversely proportional to the specific inductive

It is impossible in the existing state of human knowledge to give a
satisfactory definition of electricity. The views of various authorities
are given here to afford a basis for arriving at the general consensus
of electricians.

We have as yet no conception of electricity apart from the electrified
body; we have no experience of its independent existence. (J. E. H.

What is Electricity? We do not know, and for practical purposes it is
not necessary that we should know. (Sydney F. Walker.)

Electricity … is one of those hidden and mysterious powers of nature
which has thus become known to us through the medium of effects.
(Weale's Dictionary of Terms.)

This word Electricity is used to express more particularly the cause,
which even today remains unknown, of the phenomena that we are about to
explain. (Amédée Guillemin.)


Electricity is a powerful physical agent which manifests itself mainly
by attractions and repulsions, but also by luminous and heating effects,
by violent commotions, by chemical decompositions, and many other
phenomena. Unlike gravity, it is not inherent in bodies, but it is
evoked in them by a variety of causes … (Ganot's Physics.)

Electricity and magnetism are not forms of energy; neither are they
forms of matter. They may, perhaps, be provisionally defined as
properties or conditions of matter; but whether this matter be the
ordinary matter, or whether it be, on the other hand, that
all-pervading ether by which ordinary matter is surrounded, is a question
which has been under discussion, and which now may be fairly held to be
settled in favor of the latter view. (Daniell's Physics.)

The name used in connection with an extensive and important class of
phenomena, and usually denoting the unknown cause of the phenomena or
the science that treats of them. (Imperial Dictionary.)

Electricity. . . is the imponderable physical agent, cause, force or the
molecular movement, by which, under certain conditions, certain
phenomena, chiefly those of attraction and repulsion, . . . are
produced. (John Angell.)

It has been suggested that if anything can rightly be called
"electricity," this must be the ether itself; and that all electrical
and magnetic phenomena are simply due to changes, strains and motions in
the ether. Perhaps negative electrification. . .means an excess of
ether, and positive electrification a defect of ether, as compared with
the normal density. (W. Larden.)

Electricity is the name given to the supposed agent producing the
described condition (i. e. electrification) of bodies. (Fleeming

There are certain bodies which, when warm and dry, acquire by friction,
the property of attracting feathers, filaments of silk or indeed any
light body towards them. This property is called Electricity, and bodies
which possess it are said to be electrified. (Linnaeus Cumming.)

What electricity is it is impossible to say, but for the present it is
convenient to look upon it as a kind of invisible something which
pervades all bodies. (W. Perren Maycock.)

What is electricity? No one knows. It seems to be one manifestation of
the energy which fills the universe and which appears in a variety of
other forms, such as heat, light, magnetism, chemical affinity,
mechanical motion, etc. (Park Benjamin.)


The theory of electricity adopted throughout these lessons is, that
electricity, whatever its true nature, is one, not two; that this
Electricity, whatever it may prove to be, is not matter, and is not
energy; that it resembles both matter and energy in one respect,
however, in that it can neither be created nor destroyed. (Sylvanus P.

In Physics a name denoting the cause of an important class of phenomena
of attraction and repulsion, chemical decomposition, etc., or,
collectively, these phenomena themselves. (Century Dictionary.)

A power in nature, often styled the electric fluid, exhibiting itself,
when in disturbed equilibrium or in activity, by a circuit movement, the
fact of direction in which involves polarity, or opposition of
properties in opposite directions; also, by attraction for many
substances, by a law involving attraction between substances of unlike
polarity, and repulsion between those of like; by exhibiting accumulated
polar tension when the circuit is broken; and by producing heat, light,
concussion, and often chemical changes when the circuit passes between
the poles, or through any imperfectly conducting substance or space. It
is evolved in any disturbance of molecular equilibrium, whether from a
chemical, physical, or mechanical cause. (Webster's Dictionary.)

In point of fact electricity is not a fluid at all, and only in a few of
its attributes is it at all comparable to a fluid. Let us rather
consider electricity to be a condition into which material substances
are thrown. . .(Slingo & Brooker.)

[Transcriber's note: 2008 Dictionary: Phenomena arising from the
behavior of electrons and protons caused by the attraction of particles
with opposite charges and the repulsion of particles with the same

Electricity, Cal.
The electricity produced in the secondary of a transformer by changes of
temperature in the core. This is in addition to the regularly induced

Synonym--Acheson Effect.

Substances developing electrification by rubbing or friction; as
Gilbert, the originator of the term, applied it, it would indicate
dielectrics. He did not know that, if insulated, any substance was one
of his "electrics." A piece of copper held by a glass handle becomes
electrified by friction.

The receiving or imparting an electric charge to a surface; a term
usually applied to electrostatic phenomena.

A term in electro-therapeutics; the subjection of the human system to
electric treatment for curative, tonic or diagnostic purposes.

The science of electricity in its relation to the living organism,
whether as electricity is developed by the organism, or as it affects
the same when applied from an external source.


The relations between surface tension, the potential difference and the
electrostatic capacity of fluids in contact. Although nominally in
contact such surfaces are separated by about one-twenty-millionth of a
centimeter (1/50000000 inch) ; thus a globule of mercury and water in
which it is immersed constitute an electrostatic accumulator of definite
electrostatic capacity. Again the mercury and water being in electric
connection differ in potential by contact (see Contact Theory). A
definite surface tension is also established. Any change in one of these
factors changes the other also. A current passed through the contact
surfaces will change the surface tension and hence the shape of the
mercury globule. Shaking the globule will change its shape and capacity
and produce a current. Heating will do the same. (See Electrometer,
Capillary; and Telephone, Capillary.) Mercury and water are named as
liquids in which the phenomena are most conveniently observed. They are
observable in other parallel cases.

Electro-chemical Equivalent.
The quantity of an element or compound liberated from or brought into
combination, electrolytically, by one coulomb of electricity. The
electro-chemical equivalent of hydrogen is found by experiment to be
.0000105 gram. That of any other substance is found by multiplying this
weight by its chemical equivalent referred to hydrogen, which is its
atomic or molecular weight divided by its valency. Thus the atomic
weight of oxygen is 16, its valency is 2, its equivalent is 16/2 = 8;
its electro-chemical equivalent is equal to .0000105 X 8 = .000840 gram.

Electro-chemical Series.
An arrangement of the elements in the order of their relative electrical
affinities so that each element is electro-negative to all the elements
following it, and electro-positive to the elements preceding it. The
usual series begins with oxygen as the most electro-negative and ends
with potassium as the most electro-positive element. There is, of
course, no reason why other series of compound radicals, such as
sulphion (SO4), etc., should not also be constructed. For each liquid
acting on substances a separate series of the substances acted on may be
constructed. Thus for dilute sulphuric acid the series beginning with
the negatively charged or most attacked one is zinc, amalgamated or
pure, cadmium, iron, tin, lead, aluminum, nickel, antimony, bismuth,
copper, silver, platinum. In other liquids the series is altogether

The branch of electricity or of chemistry treating of the relations
between electric and chemical force in different compounds and
reactions. (See Electrolysis--Electrochemical series--Electro-chemical
Equivalent .)


The application of electricity to the cultivation of plants. In one
system wires are stretched or carried across the bed under the surface,
and some are connected to one pole and others to the other pole of a
galvanic battery of two or more elements. In some experiments improved
results have thus been obtained.

Another branch refers to the action of the electric arc light on
vegetation. This has an effect on vegetation varying in results.

(a) The terminal of an open electric circuit.

(b) The terminals of the metallic or solid conductors of an electric
circuit, immersed in an electrolytic solution.

(c) The terminals between which a voltaic arc is formed, always in
practice made of carbon, are termed electrodes.

(d) In electro-therapeutics many different electrodes are used whose
names are generally descriptive of their shape, character, or uses to
which they are to be applied. Such are aural electrodes for the ears,
and many others.

(e) The plates of a voltaic battery.

Electrode, Indifferent.
A term in electro-therapeutics. An electrode to which no therapeutic
action is attributed but which merely provides a second contact with the
body to complete the circuit through the same. The other electrode is
termed the therapeutic electrode.

Electrodes, Erb's Standards of.
Proposed standard sizes for medical electrodes as follows:
  Name.          Diameter.
  Fine     Electrode,   1/2  centimeter   .2      inch
  Small       "         2       "         .8        "
  Medium      "       7.5       "        3.0        "
  Large       "       6X2       "        2.4 X .8   "
  Very large  "      16x8       "        6.4 x 3.2  "

Electrodes, Non-polarizable.
In electro-therapeutics electrodes whose contact surface is virtually
porous clay saturated with zinc chloride solution. The series terminate
in amalgamated zinc ends, enclosed each in a glass tube, and closed with
clay. Contact of metal with the tissues is thus avoided.

Electrode, Therapeutic.
A term in electro-therapeutics. An electrode applied to the body for the
purpose of inducing therapeutic action, or for giving the basis for an
electric diagnosis of the case. The other electrode is applied to
complete the circuit only; it is termed the indifferent electrode.

The study of the condition of a patient by the reactions which occur at
the terminals or kathode and anode of an electric circuit applied to the
person. The reactions are divided into kathodic and anodic reactions.


Electro-dynamic. adj.
The opposite of electrostatic; a qualification of phenomena due to
current electricity.


Electro-dynamic Attraction and Repulsion.
The mutual attraction and repulsion exercised by currents of electricity
upon each other. The theory of the cause is based upon stress of the
luminiferous ether and upon the reaction of lines of force upon each
other. For a resumé of the theory see Induction, Electro-magnetic.

The laws of electricity in a state of motion; the inter-reaction of
electric currents. It is distinguished from electro-magnetic induction
as the latter refers to the production of currents by induction. The
general laws of electro-dynamics are stated under Induction,
Electro-magnetic, q. v.




Electro-dynamometer, Siemens'.
An apparatus for measuring currents by the reaction between two coils,
one fixed and one movable, through which the current to be measured
passes. It is one of the oldest commercial ammeters or current
measurers. It comprises a fixed coil of a number of convolutions and a
movable coil often of only one convolution surrounding the other. The
movable coil is suspended by a filament or thread from a spiral spring.
The spring is the controlling factor. Connection is established through
mercury cups so as to bring the two coils in series. In use the spring
and filament are adjusted by turning a milled head to which they are
connected until the coils are at right angles. Then the current is
turned on and deflects the movable coil. The milled head is turned until
the deflection is overcome. The angle through which the head is turned
is proportional to the square of the current. The movable coil must in
its position at right angles to the fixed one lie at right angles to the
magnetic meridian.

Thus in the diagram, Fig. 143 A B C D is the fixed coil; E F G H is the
movable coil; S is the spiral spring attached at K to the movable coil.
The arrows show the course of the current as it goes through the coils.

A fixture for supporting electric lamps; the analogue in electric
lighting of the gasolier or gas chandelier. Often both are combined, the
same fixture being piped and carrying gas burners, as well as being
wired and carrying electric lamps.

The separation of a chemical compound into its constituent parts or
elements by the action of the electric current. The compound may be
decomposed into its elements, as water into hydrogen and oxygen, or into
constituent radicals, as sodium sulphate into sodium and sulphion, which
by secondary reactions at once give sodium hydrate and sulphuric acid.
The decomposition proceeds subject to the laws of electrolysis. (See
Electrolysis, Laws of.) For decomposition to be produced there is for
each compound a minimum electro-motive force or potential difference
required. The current passes through the electrolyte or substance
undergoing decomposition entirely by Electrolytic Conduction, q. v. in
accordance with Grothüss' Hypothesis, q. v. The electrolyte therefore
must be susceptible of diffusion and must be a fluid.

The general theory holds that under the influence of a potential
difference between electrodes immersed in an electrolyte, the molecules
touching the electrodes are polarized, in the opposite sense for each
electrode. If the potential difference is sufficient the molecules will
give up one of their binary constituents to the electrode, and the other
constituent will decompose the adjoining molecule, and that one being
separated into the same two constituents will decompose its neighbor,
and so on through the mass until the other electrode is reached. This
one separates definitely the second binary constituent from the
molecules touching it.


Thus there is an exact balance preserved. Just as many molecules are
decomposed at one electrode as at the other, and the exact chain of
decomposition runs through the mass. Each compound electrolyzed develops
a binary or two-fold composition, and gives up one constituent to one
electrode and the other to the other.


The cut shows the assumed polarization of an electrolyte. The upper row
shows the molecules in irregular order before any potential difference
has been produced, in other words, before the circuit is closed. The
next row shows the first effects of closing the circuit, and also
indicates the polarization of the mass, when the potential difference is
insufficient for decomposition. The third row indicates the
decomposition of a chain of molecules, one constituent separating at
each pole.


Electrolysis, Laws of.
The following are the principal laws, originally discovered by
Faraday, and sometimes called Faraday's Laws of Electrolysis:

1. Electrolysis cannot take place unless the electrolyte is a conductor.
Conductor here means an electrolytic conductor, one that conducts by its
own molecules traveling, and being decomposed. (See Grothüss'

II. The energy of the electrolytic action of the current is the same
wherever exercised in different parts of the circuit.

III. The same quantity of electricity--that is the same current for the
same period----- decomposes chemically equivalent quantities of the
bodies it decomposes, or the weights of elements separated in
electrolytes by the same quantity of electricity (in coulombs or some
equivalent unit) are to each other as their chemical equivalent.

IV. The quantity of a body decomposed in a given time is proportional to
the strength of the current.

To these may be added the following:

V. A definite and fixed electro-motive force is required for the
decomposition of each compound, greater for some and less for others.
Without sufficient electro-motive force expended on the molecule no
decomposition will take place. (See Current, Convective.)

A body susceptible of decomposition by the electric current, and capable
of electrolytic conduction. It must be a fluid body and therefore
capable of diffusion, and composite in composition. An elemental body
cannot be an electrolyte.

Electrolytic Analysis.
Chemical analysis by electrolysis. The quantitative separation of a
number of metals can be very effectively executed. Thus, suppose that a
solution of copper sulphate was to be analyzed. A measured portion of
the solution would be introduced into a weighed platinum vessel. The
vessel would be connected to the zinc plate terminal of a battery. From
the other terminal of the battery a wire would be brought and would
terminate in a plate of platinum. This would be immersed in the solution
in the vessel. As the current would pass the copper sulphate would be
decomposed and eventually all the copper would be deposited in a firm
coating on the platinum. The next operations would be to wash the metal
with distilled water, and eventually with alcohol, to dry and to weigh
the dish with the adherent copper. On subtracting the weight of the dish
alone from the weight of the dish and copper, the weight of the metallic
copper in the solution would be obtained.

In similar ways many other determinations are effected. The processes of
analysis include solution of the ores or other substances to be analyzed
and their conversion into proper form for electrolysis. Copper as just
described can be precipitated from the solution of its sulphate. For
iron and many other metals solutions of their double alkaline oxalates
are especially available forms for analysis.

The entire subject has been worked out in considerable detail by
Classen, to whose works reference should be made for details of

Electrolytic Convection.
It is sometimes observed that a single cell of Daniell battery, for
instance, or other source of electric current establishing too low a
potential difference for the decomposition of water seems to produce a
feeble but continuous decomposition. This is very unsatisfactorily
accounted for by the hydrogen as liberated combining with dissolved
oxygen. (Ganot.) The whole matter is obscure. (See Current, Convection.)


Electrolytic Conduction.
Conduction by the travel of atoms or radicals from molecule to molecule
of a substance with eventual setting free at the electrodes of the atoms
or radicals as elementary molecules or constituent radicals. A substance
to be capable of acting as an electrolytic conductor must be capable of
diffusion, and must also have electrolytic conductivity. Such a body is
called an electrolyte. (See Grothüss' Hypothesis--Electrolysis--
Electrolysis, Laws of--Electro-chemical Equivalent.)

A mass, in practice always of iron, around which an electric circuit is
carried, insulated from the iron. When a current is passed through the
circuit the iron presents the characteristics of a magnet. (See
Magnetism, Ampére's Theory of--Solenoid--Lines of Force.) In general
terms the action of a circular current is to establish lines of force
that run through the axis of the circuit approximately parallel thereto,
and curving out of and over the circuit, return into themselves outside
of the circuit. If a mass of iron is inserted in the axis or elsewhere
near such current, it multiplies within itself the lines of force, q. v.
(See also Magnetic Permeability--Permeance--Magnetic Induction,
Coefficient of Magnetic Susceptibility--Magnetization, Coefficient of
Induced.) These lines of force make it a magnet. On their direction,
which again depends on the direction of the magnetizing current, depends
the polarity of the iron. The strength of an electro-magnet, below
saturation of the core (see Magnetic Saturation), is proportional nearly
to the ampere-turns, q. v. More turns for the same current or more
current for the same turns increase its strength.

In the cut is shown the general relation of current, coils, core and
line of force. Assume that the magnet is looked at endwise, the observer
facing one of the poles; then if the current goes around the core in the
direction opposite to that of the hands of a clock, such pole will be
the north pole. If the current is in the direction of the hands of a
clock the pole facing the observer will be the south pole. The whole
relation is exactly that of the theoretical Ampérian currents, already
explained. The direction and course of the lines of force created are
shown in the cut.

The shapes of electro-magnets vary greatly. The cuts show several forms
of electro- magnets. A more usual form is the horseshoe or double limb
magnet, consisting generally of two straight cores, wound with wire and
connected and held parallel to each other by a bar across one end, which
bar is called the yoke.

In winding such a magnet the wire coils must conform, as regards
direction of the current in them to the rule for polarity already cited.
If both poles are north or both are south poles, then the magnet cannot
be termed a horseshoe magnet, but is merely an anomalous magnet. In the
field magnets of dynamos the most varied types of electro-magnets have
been used. Consequent poles are often produced in them by the direction
of the windings and connections.

To obtain the most powerful magnet the iron core should be as short and
thick as possible in order to diminish the reluctance of the magnetic
circuit. To obtain a greater range of action a long thin shape is
better, although it involves waste of energy in its excitation.




Electro-magnet, Annular.
An electro-magnet consisting of a cylinder with a circular groove cut in
its face, in which groove a coil of insulated wire is placed. On the
passage of a current the iron becomes polarized and attracts an armature
towards or against its grooved face. The cut shows the construction of
an experimental one. It is in practice applied to brakes and clutches.
In the cut of the electro-magnetic brake (see Brake, Electro-magnetic),
C is the annular magnet receiving its current through the brushes, and
pressed when braking action is required against the face of the moving
wheel. The same arrangement, it can be seen, may apply to a clutch.



Electro-magnet, Bar.
A straight bar of iron surrounded with a magnetizing coil of wire. Bar
electromagnets are not much used, the horseshoe type being by far the
more usual.

Electro-magnet, Club-foot.
An electro-magnet, one of whose legs only is wound with wire, the other
being bare.


Electro-magnet, Hinged.
An electro-magnet whose limbs are hinged at the yoke. On excitation by a
current the poles tend to approach each other.


Electro-magnetic Attraction and Repulsion.
The attraction and repulsion due to electromagnetic lines of force,
which lines always tend to take as short a course as possible and also
seek the medium of the highest permeance. This causes them to
concentrate in iron and steel or other paramagnetic substance and to
draw them towards a magnet by shortening the lines of force connecting
the two. It is exactly the same attraction as that of the permanent
magnet for its armature, Ampére's theory bringing the latter under the
same title. In the case of two magnets like poles repel and unlike
attract. In the case of simple currents, those in the same direction
attract and those in opposite directions repel each other. This refers
to constant current reactions. Thus the attraction of unlike poles of
two magnets is, by the Ampérian theory, the attraction of two sets of
currents of similar direction, as is evident from the diagram. The
repulsion of like poles is the repulsion of unlike currents and the same
applies to solenoids, q. v. (See Magnetism and do. Ampére's Theory
of--Induction, Electro-dynamic--Electro-magnetic Induction.)


Electro-magnetic Control.
Control of a magnet, iron armature, or magnetic needle in a
galvanometer, ammeter, voltmeter or similar instrument by an
electro-magnetic field, the restitutive force being derived from an
electro-magnet. The restitutive force is the force tending to bring the
index to zero.

Electro-magnetic Field of Force.
A field of electro-magnetic lines of force, q. v., established through
the agency of an electric current. A wire carrying a current is
surrounded by circular concentric lines of force which have the axis of
the wire as the locus of their centres. Electro-magnets produce lines of
force identical with those produced by permanent magnets. (See Field of
Force--Magnetic Field of Force--Controlling Field--Deflecting Field.)

Electro-magnetic Induction.
When two currents of unlike direction are brought towards each other,
against their natural repulsive tendency work is done, and the
consequent energy takes the form of a temporary increase in both
currents. When withdrawn, in compliance with the natural tendency of
repulsion, the currents are diminished in intensity, because energy is
not expended on the withdrawal, but the withdrawal is at the expense of
the energy of the system. The variations thus temporarily produced in
the currents are examples of electro-magnetic induction. The currents
have only the duration in each case of the motion of the circuits. One
circuit is considered as carrying the inducer current and is termed the
primary circuit and its current the primary current, the others are
termed the secondary circuit and current respectively. We may assume a
secondary circuit in which there is no current. It is probable that
there is always an infinitely small current at least, in every closed
circuit. Then an approach of the circuits will induce in the secondary
an instantaneous current in the reverse direction. On separating the two
circuits a temporary current in the same direction is produced in the


A current is surrounded by lines of force. The approach of two circuits,
one active, involves a change in the lines of force about the secondary
circuit. Lines of force and current are so intimately connected that a
change in one compels a change in the other. Therefore the induced
current in the secondary may be attributed to the change in the field of
force in which it lies, a field maintained by the primary circuit and
current. Any change in a field of force induces a current or change of
current in any closed circuit in such field, lasting as long as the
change is taking place. The new current will be of such direction as to
oppose the change. (See Lenz's Law.)

The action as referred to lines of force may be figured as the cutting
of such lines by the secondary circuit, and such cutting may be brought
about by moving the secondary in the field. (See Lines of Force--Field
of Force.) The cutting of 1E8 lines of force per second by a closed
circuit induces an electro-motive force of one volt. (See Induction,
Mutual, Coefficient of.)

Electro-magnet, Iron Clad.
A magnet whose coil and core are encased in a iron jacket, generally
connected to one end of the core. This gives at one end two poles, one
tubular, the other solid, and concentric with each other. It is
sometimes called a tubular magnet.

Electro-magnet, One Coil.
An electro-magnet excited by one coil. In some dynamos the field magnets
are of this construction, a single coil, situated about midway between
the poles, producing the excitation.

Electro-magnetic Leakage.
The leakage of lines of force in an electro-magnet; the same as magnetic
leakage. (See Magnetic Leakage.)

Electro-magnetic Lines of Force.
The lines of force produced in an electro-magnetic field. They are
identical with Magnetic Lines of Force, q. v. (See also Field of
Force-Line of Force.)

Electro-magnetic Stress.
The stress in an electro-magnetic field of force, showing itself in the
polarization of light passing through a transparent medium in such a
field. (See Magnetic Rotary Polarization.)

Electro-magnetic Theory of Light.
This theory is due to J. Clark Maxwell, and the recent Hertz experiments
have gone far to prove it. It holds that the phenomena of light are due
to ether waves, identical in general factors with those produced by
electro-magnetic induction of alternating currents acting on the ether.
In a non-conductor any disturbance sets an ether wave in motion owing to
its restitutive force; electricity does not travel through such a
medium, but can create ether waves in it. Therefore a non-conductor of
electricity is permeable to waves of ether or should transmit light, or
should be transparent. A conductor on the other hand transmits
electrical disturbances because it has no restitutive force and cannot
support an ether wave. Hence a conductor should not transmit light, or
should be opaque. With few exceptions dielectrics or non-conductors are
transparent, and conductors are opaque.


Again, the relation between the electrostatic and electro-magnet units
of quantity is expressed by 1 : 30,000,000,000; the latter figure in
centimeters gives approximately the velocity of light. The
electro-magnetic unit depending on electricity in motion should have
this precise relation if an electro-magnetic disturbance was propagated
with the velocity of light. If an electrically charged body were whirled
around a magnetic needle with the velocity of light, it should act in
the same way as a current circulating around it. This effect to some
extent has been shown experimentally by Rowland.

A consequence of these conclusions is (Maxwell) that the specific
inductive capacity of a non-conductor or dielectric should be equal to
the square of its index of refraction for waves of infinite length. This
is true for some substances--sulphur, turpentine, petroleum and benzole.
In others the specific inductive capacity is too high, e. g., vegetable
and animal oils, glass, Iceland spar, fluor spar, and quartz.

Electro-magnetic Unit of Energy.
A rate of transference of energy equal to ten meg-ergs per second.

The branch of electrical science treating of the magnetic relations of a
field of force produced by a current, of the reactions of
electro-magnetic lines of force, of the electromagnetic field of force,
of the susceptibility, permeability, and reluctance of diamagnetic and
paramagnetic substances, and of electro-magnets in general.

Electro-magnet, Long Range.
An electro-magnet so constructed with extended pole pieces or otherwise,
as to attract its armature with reasonably constant force over a
considerable distance. The coil and plunger, q. v., mechanisms
illustrate one method of getting an extended range of action. When a
true electro-magnet is used, one with an iron core, only a very limited
range is attainable at the best. (See Electro-magnet, Stopped Coil--do.

Electro-magnet, Plunger.
An electro-magnet with hollow coils, into which the armature enters as a
plunger. To make it a true electro-magnet it must have either a yoke,
incomplete core, or some polarized mass of iron.

Electro-magnet, Polarized.
An electro-magnet consisting of a polarized or permanently magnetized
core wound with magnetizing coils, or with such coils on soft iron cores
mounted on its ends. The coils may be wound and connected so as to
cooperate with or work against the permanent magnet on which it is
mounted. In Hughes' magnet shown in the cut it is mounted in opposition,
so that an exceedingly feeble current will act to displace the armature,
a, which is pulled away from the magnet by a spring, s.



Electro-magnets, Interlocking.
Electro-magnets so arranged that their armatures interlock. Thus two
magnets, A A and B B, may be placed with their armatures, M and N, at
right angles and both normally pulled away from the poles. When the
armature M is attracted a catch on its end is retained by a hole in the
end of the other armature N, and when the latter armature N is attracted
by its magnet the armature M is released. In the mechanism shown in the
cut the movements of the wheel R are controlled. Normally it is held
motionless by the catch upon the bottom of the armature M, coming
against the tooth projecting from its periphery. A momentary current
through the coils of the magnet A A releases it, by attracting M, which
is caught and retained by N, and leaves it free to rotate. A momentary
current through the coils of the magnet B B again releases M, which
drops down and engages the tooth upon R and arrests its motion.



Electro-magnet, Stopped Coil.
An electro-magnet consisting of a tubular coil, in which a short fixed
core is contained, stopping up the aperture to a certain distance, while
the armature is a plunger entering the aperture. This gives a longer
range of action than usual.

Electro-magnet, Surgical.
An electro-magnet, generally of straight or bar form, fitted with
different shaped pole pieces, used for the extraction of fragments of
iron or steel from the eyes. Some very curious cases of successful
operations on the eyes of workmen, into whose eyes fragments of steel or
iron had penetrated, are on record.

Electro-medical Baths.
A bath for the person provided with connections and electrodes for
causing a current of electricity of any desired type to pass through the
body of the bather. Like all electro-therapeutical treatment, it should
be administered under the direction of a physician only.

(a) In the reduction of ores the electric current has been proposed but
never extensively used, except in the reduction of aluminum and its
alloys. (See Reduction of Ores, Electric.)

(b) Electro-plating and deposition of metal from solutions is another
branch. (See Electroplating and Electrotyping.)

(c) The concentration of iron ores by magnetic attraction may come under
this head. (See Magnetic Concentration of Ores.)

An instrument for use in the measurement of potential difference, by the
attraction or repulsion of statically charged bodies. They are
distinguished from galvanometers as the latter are really current
measurers, even if wound for use as voltmeters, depending for their
action upon the action of the current circulating in their coils.

Electrometer, Absolute.
An electrometer designed to give directly the value of a charge in
absolute units. In one form a plate, a b, of conducting surface is
supported or poised horizontally below a second larger plate C, also of
conducting surface. The poised plate is surrounded by a detached guard
ring--an annular or perforated plate, r g r' g'--exactly level and even
with it as regards the upper surface. The inner plate is carried by a
delicate balance. In use it is connected to one of the conductors and
the lower plate to earth or to the other. The attraction between them is
determined by weighing. By calculation the results can be made absolute,
as they depend on actual size of the plates and their distance, outside
of the potential difference of which of course nothing can be said. If S
is the area of the disc, d the distance of the plates, V-V1 the
difference of their potential, which is to be measured, and F the force
required to balance their attraction, we have:

F = ( ( V - V1 )^2 * S )  / ( 8 * PI * d^2 )


If  V = 0 this reduces to

   F =  ( V^2 * S ) / ( 8 * PI * d^2 )  (2)
  V =  d * SquareRoot( (8 * PI * F ) / S )   (3)

As F is expressed as a weight, and S and a as measures of area and
length, this gives a means of directly obtaining potential values in
absolute measure. (See Idiostatic Method--Heterostatic Method.)

Synonyms--Attracted Disc Electrometer--Weight Electrometer.


In some forms the movable disc is above the other, and supported at the
end of a balance beam. In others a spring support, arranged so as to
enable the attraction to be determined in weight units, is adopted. The
cuts, Figs. 152 and 154, show one of the latter type, the portable
electrometer. The disc portion is contained within a cylindrical vessel.


Referring to Fig. 152  g is the stationary disc, charged through the
wire connection r; f is the movable disc, carried by a balance beam
poised at i on a horizontal and transverse stretched platinum wire,
acting as a torsional spring. The position of the end k of the balance
beam shows when the disc f is in the plane of the guard ring h h. The
end k is forked horizontally and a horizontal sighting wire or hair is
fastened across the opening of the fork. When the hair is midway between
two dots on a vertical scale the lever is in the sighted position, as it
is called, and the disc is in the plane of the guard ring.



The general construction is seen in Fig. 154. There the fixed disc D is
carried by insulating stem g1. The charging electrode is supported by an
insulating stem g2, and without contact with the box passes out of its
cover through a guard tube E, with cover, sometimes called umbrella, V.
The umbrella is to protect the apparatus from air currents. At m is the
sighting lens. H is a lead box packed with pumice stone, moistened with
oil of vitriol or concentrated sulphuric acid, to preserve the
atmosphere dry. Before use the acid is boiled with some ammonium
sulphate to expel any corrosive nitrogen oxides, which might corrode the

In use the upper disc is charged by its insulated electrode within the
tube E; the movable disc is charged if desired directly through the case
of the instrument. The upper disc is screwed up or down by the
micrometer head M, until the sighted position is reached. The readings
of the micrometer on the top of the case give the data for calculation.



Electrometer, Capillary.
An electrometer for measuring potential difference by capillary action,
which latter is affected by electrostatic excitement. A tube A contains
mercury; its end drawn out to a fine aperture dips into a vessel B which
contains dilute sulphuric acid with mercury under it, as shown. Wires
running from the binding-posts a and b connect one with the mercury in
A, the other with that in B. The upper end of the tube A connects with a
thick rubber mercury reservoir T, and manometer H. The surface tension
of the mercury-acid film at the lower end of the tube A keeps all in
equilibrium. If now a potential difference is established between a and
b, as by connecting a battery thereto, the surface tension is increased
and the mercury rises in the tube B. By screwing down the compressing
clamp E, the mercury is brought back to its original position. The
microscope M is used to determine this position with accuracy. The
change in reading of the manometer gives the relation of change of
surface tension and therefore of potential. Each electrometer needs
special graduation or calibration, but is exceedingly sensitive and
accurate. It cannot be used for greater potential differences than .6
volt, but can measure .0006 volt. Its electrostatic capacity is so small
that it can indicate rapid changes. Another form indicates potential
difference by the movement of a drop of sulphuric acid in a horizontal
glass tube, otherwise filled with mercury, and whose ends lead into two
mercury cups or reservoirs. The pair of electrodes to be tested are
connected to the mercury vessels. The drop moves towards the negative
pole, and its movement for small potential differences (less than one
volt) is proportional to the electro-motive force or potential


Electrometer Gauge.
An absolute electrometer (see Electrometer, Absolute) forming an
attachment to a Thomson quadrant electrometer. It is used to test the
potential of the flat needle connected with the inner surface of the
Leyden jar condenser of the apparatus. This it does by measuring the
attraction between itself and an attracting disc, the latter connected
by a conductor with the interior of the jar.

Electrometer, Lane's.
A Leyden jar with mounted discharger, so that when charged to a certain
point it discharges itself. It is connected with one coating of any jar
whose charge is to be measured, which jar is then charged by the other
coating. As the jar under trial becomes charged to a certain point the
electrometer jar discharges itself, and the number of discharges is the
measure of the charge of the other jar. It is really a unit jar, q. v.




Electrometer, Quadrant.
(a) Sir William Thomson's electrometer, a simple form of which is shown
in the cut, consists of four quadrants of metal placed horizontally;
above these a broad flat aluminum needle hangs by a very fine wire,
acting as torsional suspension. The quadrants are insulated from each
other, but the opposite ones connect with each other by wires. The
apparatus is adjusted so that, when the quadrants are in an unexcited
condition the needle is at rest over one of the diametrical divisions
between quadrants. The needle by its suspension wire is in communication
with the interior of a Leyden jar which is charged. The whole is covered
with a glass shade, and the air within is kept dry by a dish of
concentrated sulphuric acid so that the jar retains its charge for a
long time and keeps the needle at approximately a constant potential. If
now two pairs of quadrants are excited with opposite electricities, as
when connected with the opposite poles of an insulated galvanic cell,
the needle is repelled by one pair and attracted by the other, and
therefore rotates through an arc of greater or less extent. A small
concave mirror is attached above the needle and its image is reflected
on a graduated screen. This makes the smallest movement visible.
Sometimes the quadrants are double, forming almost a complete box,
within which the needle moves.

(b) Henley's quadrant electrometer is for use on the prime conductor of
an electric machine, for roughly indicating the relative potential
thereof. It consists of a wooden standard attached perpendicularly to
the conductor. Near one end is attached a semi-circular or quadrant arc
of a circle graduated into degrees or angular divisions. An index,
consisting of a straw with a pith-bell attached to its end hangs from
the center of curvature of the arc. When the prime conductor is charged
the index moves up over the scale and its extent of motion indicates the
potential relatively.

When the "quadrant electrometer" is spoken of it may always be assumed
that Sir William Thomson's instrument is alluded to. Henley's instrument
is properly termed a quadrant electroscope. (See Electroscope.)

Electro-motive Force.
The cause which produces currents of electricity. In general it can be
expressed in difference of potentials, although the term electro-motive
force should be restricted to potential difference causing a current. It
is often a sustained charging of the generator terminals whence the
current is taken. Its dimensions are

(work done/the quantity of electricity involved),

or ( M * (L^2) /(T^2 ) ) / ((M^.5) * (L^.5)) = ( (M^.5) * (L^1.5) ) /(T^2)

The practical unit of electro-motive force is the volt, q. v. It is
often expressed in abbreviated form, as E. M. D. P., or simply as D. P.,
i. e., potential difference.

Electro-motive force and potential difference are in many cases
virtually identical, and distinctions drawn between them vary with
different authors. If we consider a closed electric circuit carrying a
current, a definite electro-motive force determined by Ohm's law from
the resistance and current obtains in it. But if we attempt to define
potential difference as proper to the circuit we may quite fail.
Potential difference in a circuit is the difference in potential between
defined points of such circuit. But no points in a closed circuit can be
found which differ in potential by an amount equal to the entire
electro-motive force of the circuit. Potential difference is properly
the measure of electro-motive force expended on the portion of a circuit
between any given points. Electro-motive force of an entire circuit, as
it is measured, as it were, between two consecutive points but around
the long portion of the circuit, is not conceivable as merely potential
difference. Taking the circle divided in to degrees as an analogy, the
electro-motive force of the entire circuit might be expressed as 360º,
which are the degrees intervening between two consecutive points,
measured the long way around the circle. But the potential difference
between the same two points would be only 1º, for it would be measured
by the nearest path.

[Transcriber's notes: If 360º is the "long" way, 0º is the "short". A
formal restatement of the above definition of EMF: "If a charge Q passes
through a device and gains energy U, the net EMF for that device is the
energy gained per unit charge, or U/Q. The unit of EMF is a volt, or
newton-meter per coulomb."]


Electro-motive Force, Counter.
A current going through a circuit often has not only true or ohmic
resistance to overcome, but meets an opposing E. M. F. This is termed
counter-electro-motive force. It is often treated in calculations as
resistance, and is termed spurious resistance. It may be a part of the
impedance of a circuit.

In a primary battery hydrogen accumulating on the negative plate
develops counter E. M. F. In the voltaic arc the differential heating of
the two carbons does the same. The storage battery is changed by a
current passing in the opposite direction to its own natural current;
the polarity of such a battery is counter E. M. F.

Electro-motive Force, Unit.
Unit electro-motive force is that which is created in a conductor moving
through a magnetic field at such a rate as to cut one unit line of force
per second. It is that which must be maintained in a circuit of unit
resistance to maintain a current of unit quantity therein. It is that
which must be maintained between the ends of a conductor in order that
unit current may do unit work in a second.

Electro-motive Intensity.
The force acting upon a unit charge of electricity. The mean force is
equal to the difference of potential between two points within the field
situated one centimeter apart, such distance being measured along the
lines of force. The term is due to J. Clerk Maxwell.

Electro-motive Series.
Arrangement of the metals and carbon in series with the most
electro-positive at one end, and electronegative at the other end. The
following are examples for different exciting liquids:

Dilute Sulphuric   Dilute Hydrochloric   Caustic   Potassium
Acid               Acid.                 Potash.   Sulphide.

Zinc               Zinc                  Zinc      Zinc
Cadmium            Cadmium               Tin       Copper
Tin                Tin                   Cadmium   Cadmium
Lead               Lead                  Antimony  Tin
Iron               Iron                  Lead      Silver
Nickel             Copper                Bismuth   Antimony
Bismuth            Bismuth               Iron      Lead
Antimony           Nickel                Copper    Bismuth
Copper             Silver                Nickel    Nickel
Silver             Antimony              Silver    Iron

In each series the upper metal is the positive, dissolved or attacked


An invention of Thomas A. Edison. A cylinder of chalk, moistened with
solution of caustic soda, is mounted so as to be rotated by a handle. A
diaphragm has an arm connected to its center. This arm is pressed
against the surface of the cylinder by a spring. When the cylinder is
rotated, a constant tension is exerted on the diaphragm. If a current is
passed through the junction of arm and cylinder the electrolytic action
alters the friction so as to change the stress upon the diaphragm.

If the current producing this effect is of the type produced by the
human voice through a microphone the successive variations in strain
upon the diaphragm will cause it to emit articulate sounds. These are
produced directly by the movement of the cylinder, the electrolytic
action being rather the regulating portion of the operation. Hence very
loud sounds can be produced by it. This has given it the name of the
loud- speaking telephone.

The same principle may be applied in other ways. But the practical
application of the motograph is in the telephone described.


This term is sometimes applied to a current generator, such as a voltaic

Electro-muscular Excitation.
A term in medical electricity indicating the excitation of muscle as the
effect of electric currents of any kind.

Electro-negative. adj.
Appertaining to negative electrification; thus of the elements oxygen is
the most electro-negative, because if separated by electrolytic action
from any combination, it will be charged with negative electricity.


The branch of natural science treating of the relations between light
and electricity. Both are supposed to be phenomena of or due to the
luminiferous ether. To it may be referred the following:

(a) Electro-magnetic Stress and Magnetic Rotary Polarization;

(b) Dielectric Strain; all of which may be referred to in this book;

(c) Change in the resistance of a conductor by changes in light to which
it is exposed (see Selenium);

(d) The relation of the index of refraction of a dielectric to the
dielectric constant (see Electro-magnetic Theory of Light);

(e) The identity (approximate) of the velocity of light in centimeters
and the relative values of the electrostatic and electro-magnet units
of intensity, the latter being 30,000,000,000 times greater than the
former, while the velocity of light is 30,000,000,000 centimeters per

Electrophoric Action.
The action of an electrophorous; utilized in influence machines. (See


An apparatus for the production of electric charges of high potential by
electrostatic induction, q. v. It consists of a disc of insulating
material B, such as resin or gutta percha, which is held in a shallow
metal-lined box or form. The disc may be half an inch thick and a foot
or more in diameter, or may be much smaller and thinner. A metal disc A,
smaller in diameter is provided with an insulating handle which may be
of glass, or simply silk suspension strings. To use it the disc B is
excited by friction with a cat-skin or other suitable substance. The
metallic disc is then placed on the cake of resin exactly in its centre,
so that the latter disc or cake projects on all sides. Owing to
roughness there is little real electric contact between the metal and
dielectric. On touching the metal disc a quantity of negative
electricity escapes to the earth. On raising it from the cake it comes
off excited positively, and gives a spark and is discharged. It can be
replaced, touched, removed and another spark can be taken from it, and
so on as long as the cake stays charged.

The successive discharges represent electrical energy expended. This is
derived from the muscular energy expended by the operator in separating
the two discs when oppositely excited. As generally used it is therefore
an apparatus for converting muscular or mechanical energy into electric


The science of the electric phenomena of the animal system. It may also
be extended to include plants. The great discovery of Galvani with the
frog's body fell into this branch of science. The electric fishes,
gymnotus, etc., present intense phenomena in the same.

The deposition by electrolysis of a coating of metal upon a conducting
surface. The simplest system makes the object to be plated the negative
electrode or plate in a galvanic couple. Thus a spoon or other object
may be connected by a wire to a plate of zinc. A porous cup is placed
inside a battery jar. The spoon is placed in the porous cup and the zinc
outside it. A solution of copper sulphate is placed in the porous cup,
and water with a little sodium or zinc sulphate dissolved in it,
outside. A current starts through the couple, and copper is deposited on
the spoon.

A less primitive way is to use a separate battery as the source of
current; to connect to the positive plate by a wire the object to be
plated, and a plate of copper, silver, nickel or other metal to the
other pole of the battery. On immersing both object and plate (anode) in
a bath of proper solution the object will become plated.

In general the anode is of the same material as the metal to be
deposited, and dissolving keeps up the strength of the bath. There are a
great many points of technicality involved which cannot be given here.
The surface of the immersed object must be conductive. If not a fine
wire network stretched over it will gradually fill up in the bath and
give a matrix. More generally the surface is made conductive by being
brushed over with plumbago. This may be followed by a dusting of iron
dust, followed by immersion in solution ot copper sulphate. This has the
effect of depositing metallic copper over the surface as a starter for
the final coat.

Attention must be paid to the perfect cleanliness of the objects, to the
condition of the bath, purity of anodes and current density.

Voltaic batteries are largely used for the current as well as special
low resistance dynamos. Thermo-electric batteries are also used to some
extent but not generally.

Electro-pneumatic Signals.
Signals, such as railroad signals or semaphores, moved by compressed
air, which is controlled by valves operated by electricity. The House
telegraph, which was worked by air controlled by electricity, might come
under this term, but it is always understood as applied to railroad
signals, or their equivalent.


Electropoion Fluid.
An acid depolarizing solution for use in zinc-carbon couples, such as
the Grenet battery. The following are formulae for its preparation:

(a) Dissolve one pound of potassium bichromate in ten pounds of water,
to which two and one-half pounds of concentrated sulphuric acid have
been gradually added. The better way is to use powdered potassium
bichromate, add it to the water first, and then gradually add the
sulphuric acid with constant stirring.

(b) To three pints of water add five fluid ounces of concentrated
sulphuric acid; add six ounces pulverized potassium bichromate.

(c) Mix one gallon concentrated sulphuric acid and three gallons of
water. In a separate vessel dissolve six pounds potassium bichromate in
two gallons of boiling water. Mix the two.

The last is the best formula. Always use electropoion fluid cold. (See
Trouvé's Solution--Poggendorff's Solution--Kakogey's Solution--
Tissandrier's Solution--Chutaux's Solution.)

Electro-positive. adj.
Appertaining to positive electrification; thus potassium is the most
electro-positive of the elements. (See Electro-negative.)

The introduction into the system of a platinum point or needle,
insulated with vulcanite, except near its point, and connected as the
anode of a galvanic battery. The kathode is a metal one, covered with a
wet sponge and applied on the surface near the place of puncture. It is
used for treatment of aneurisms or diseased growths, and also for
removal of hair by electrolysis. (See Hair, Removal of by Electrolysis.)


Electro-receptive. adj.
A term applied to any device or apparatus designed to receive and absorb
electric energy. A motor is an example of an electro-receptive

An apparatus for indicating the presence of an electric charge, and also
for determining the sign, or whether the charge is positive or negative.
The simplest form consists of a thread doubled at its centre and hung
therefrom. On being charged, or on being connected to a charged body the
threads diverge. A pair of pith balls may be suspended in a similar way,
or a couple of strips of gold leaf within a flask (the gold leaf
electroscope). To use an electroscope to determine the sign of the
charge it is first slightly charged. The body to be tested is then
applied to the point of suspension, or other charging point. If at once
further repelled the charge of the body is of the same sign as the
slight charge first imparted to the electroscope leaves; the leaves as
they become more excited will at once diverge more. If of different sign
they will at first approach as their charge is neutralized and will
afterwards diverge.

The gold-leaf electroscope is generally enclosed in a glass bell jar or
flask. Sometimes a pair of posts rise, one on each side, to supply
points of induction from the earth to intensify the action. (See
Electrometer, Quadrant--Electroscope, Gold leaf, and others.)


Electroscope, Bennett's.
A gold-leaf electroscope, the suspended leaves of which are contained in
a glass shade or vessel of dry air. On the inside of the glass shade are
two strips of gold leaf, which rise from the lower edge a short
distance, being pasted to the glass, and connected to the ground. These
act by induction to increase the sensitiveness of the instruments.

Electroscope, Bohenberger's.
A condensing electroscope (see Electroscope, Condensing) with a single
strip of gold leaf suspended within the glass bell. This is at an equal
distance from the opposite poles of two dry piles (see Zamboni's Dry
Pile) standing on end, one on each side of it. As soon as the leaf is
excited it moves toward one and away from the other pile, and the sign
of its electrification is shown by the direction of its motion.

Electroscope, Condensing.
A gold leaf electroscope, the glass bell of which is surmounted by an
electrophorous or static condenser, to the lower plate of which the
leaves of gold are suspended or connected.

In use the object to be tested is touched to the lower plate, and the
upper plate at the same time is touched by the finger. The plates are
now separated. This reduces the capacity of the lower plate greatly and
its charge acquires sufficient potential to affect the leaves, although
the simple touching may not have affected them at all.

Electroscope, Gold Leaf.
An electroscope consisting of two leaves of gold leaf hung in contact
with each other from the end of a conductor. When excited they diverge.
The leaves are enclosed in a glass vessel.



Electroscope, Pith Ball.
Two pith balls suspended at opposite ends of a silk thread doubled in
the middle. When charged with like electricity they repel each other.
The extent of their repulsion indicates the potential of their charge.

Electrostatic Attraction and Repulsion.
The attraction and repulsion of electrostatically charged bodies for
each other, shown when charged with electricity. If charged with
electricity of the same sign they repel each other. If with opposite
they attract each other. The classic attraction and subsequent repulsion
of bits of straw and chaff by the excited piece of amber is a case of
electrostatic attraction and repulsion. (See Electricity,
Static--Electrostatics--Coulomb's Laws of Electrostatic Attraction and

Electrostatic Induction, Coefficient of.
The coefficient expressing the ratio of the charge or change of charge
developed in one body to the potential of the inducing body.

Electrostatic Lines of Force.
Lines of force assumed to exist in an electrostatic field of force, and
to constitute the same. In general they correspond in action and
attributes with elcctro-magnetic lines of force. They involve in almost
all cases either a continuous circuit, or a termination at both ends in
oppositely charged surfaces.




The cut, Fig. 161, shows the general course taken by lines of force
between two excited surfaces when near together. Here most of them are
straight lines reaching straight across from surface to surface, while a
few of them arch across from near the edges, tending to spread. If the
bodies are drawn apart the spreading tendency increases and the
condition of things shown in the next cut, Fig. 162, obtains. There is
an axial line whose prolongations may be supposed to extend
indefinitely, as occupying a position of unstable equilibrium. Here the
existence of a straight and unterminated line of force may be assumed.

A direction is predicated to lines of force corresponding with the
direction of an electric current. They are assumed to start from a
positively charged and to go towards a negatively charged surface. A
positively charged body placed in an electrostatic field of force will
be repelled from the region of positive into or towards the region of
negative potential following the direction of the lines of force, not
moving transversely to them, and having no transverse component in its

[Transcriber's note: More precisely, "A positively charged body placed
in an electrostatic field of force will be repelled from the region of
positive into or towards the region of negative potential ACCELERATING
in the direction of the lines of force, not ACCELERATING transversely to
them, and having no transverse component in its ACCELERATION."
Previously acquired momentum can produce a transverse component of

The division of electric science treating of the phenomena of electric
charge, or of electricity in repose, as contrasted with electro-dynamics
or electricity in motion or in current form. Charges of like sign repel,
and of unlike sign attract each other. The general inductive action is
explained by the use of the electrostatic field of force and
electrostatic lines of force, q. v. The force of attraction and
repulsion of small bodies or virtual points, which are near enough to
each other, vary as the square of the distance nearly, and with the
product of the quantities of the charges of the two bodies.

Electrostatic Refraction.
Dr. Kerr found that certain dielectrics exposed to electric strain by
being placed between two oppositely excited poles of a Holtz machine or
other source of very high tension possess double refracting powers, in
other words can rotate a beam of polarized light, or can develop two
complimentary beams from common light. Bisulphide of carbon shows the
phenomenon well, acting as glass would if the glass were stretched in
the direction of the electrostatic lines of force. To try it with glass,
holes are drilled in a plate and wires from an influence machine are
inserted therein. The discharge being maintained through the glass it
polarizes light.

Synonym--Kerr Effect.

Electrostatic Series.
A table of substances arranged in the order in which they are
electrostatically charged by contact, generally by rubbing against each
other. The following series is due to Faraday. The first members become
positively excited when rubbed with any of the following members, and
vice versa. The first elements correspond to the carbon plate in a
galvanic battery, the succeeding elements to the zinc plate.

Cat, and Bear-skin--Flannel--Ivory--Feathers--Rock Crystal--Flint
Glass--Cotton--Linen--Canvas--White Silk--the Hand--Wood--Shellac--the
Metals (Iron-Copper-Brass-Tin-Silver-Platinum)--Sulphur. There are some
irregularities. A feather lightly drawn over canvas is negatively
electrified; if drawn through folds pressed against it it is positively
excited. Many other exceptions exist, so that the table is of little


Electrostatic Stress.
The stress produced upon a transparent medium in an electrostatic field
of force by which it acquires double refracting or polarizing properties
as regards the action of such medium upon light. (See Electrostatic

Electro-therapeutics or Therapy.
The science treating of the effects of electricity upon the animal
system in the treatment and diagnosis of disease.

An altered condition of functional activity occurring in a nerve
subjected to the passage of an electric current. If the activity is
decreased, which occurs near the anode, the state is one of
anelectrotonus, if the activity is increased which occurs near the
kathode the condition is one of kathelectrotonus.

The reproduction of a form of type or of an engraving or of the like by
electroplating, for printing purposes. The form of type is pressed upon
a surface of wax contained in a shallow box. The wax is mixed with
plumbago, and if necessary some more is dusted and brushed over its
surface and some iron dust is sprinkled over it also. A matrix or
impression of the type is thus obtained, on which copper is deposited by
electroplating, q. v.

Element, Chemical.
The original forms of matter that cannot be separated into constituents
by any known process. They are about seventy in number. Some of the
rarer ones are being added to or cancelled with the progress of chemical
discovery. For their electric relations see Electro-chemical
Equivalents--Electro-chemical Series.

The elements in entering into combination satisfy chemical affinity and
liberate energy, which may take the form of electric energy as in the
galvanic battery, or of heat energy, as in the combustion of carbon or
magnesium. Therefore an uncombined element is the seat of potential
energy. (See Energy, Potential.) In combining the elements always
combine in definite proportions. A series of numbers, one being proper
to each element which denote the smallest common multipliers of these
proportions, are called equivalents. Taking the theory of valency into
consideration the product of the equivalents by the valencies gives the
atomic weights.


Element, Mathematical.
A very small part of anything, corresponding in a general way to a
differential, as the element of a current.

Element of a Battery Cell.
The plates in a galvanic couple are termed elements, as the carbon and
zinc plates in a Bunsen cell. The plate unattacked by the solution, as
the carbon plate in the above battery, is termed the negative plate or
element; the one attacked, as the zinc plate, is termed the positive
plate or element.

Synonym--Voltaic Element.

Elements, Electrical Classification of.
This may refer to Electro-chemical Series, Electrostatic Series, or
Thermo-electric Series, all of which may be referred to.

Element, Thermo-electric.
One of the metals or other conductors making a thermo-electric couple,
the heating of whose junction produces electro-motive force and a
current, if on closed circuit. The elements of a couple are respectively
positive and negative, and most conductors can be arranged in a series
according to their relative polarity. (See Thermo-electric Series.)

The throw of the magnetic needle. (See Throw.)


Embosser, Telegraph.
A telegraphic receiver giving raised characters on a piece of paper. It
generally refers to an apparatus of the old Morse receiver type, one
using a dry point stylus, which pressing the paper into a groove in the
roller above the paper, gave raised characters in dots and lines.



E. M. D. P.
Abbreviation for "electro-motive difference of potential" or for
electro-motive force producing a current as distinguished from mere
inert potential difference.

E. M. F.
Abbreviation for "electro-motive force."

Fig. 164. END-ON METHOD.

End-on Method.
A method of determining the magnetic moment of a magnet. The magnet
under examination, N S, is placed at right angles to the magnetic
meridian, M O R, and pointing directly at or "end on" to the centre of a
compass needle, n s. From the deflection a of the latter the moment is

Endosmose, Electric.
The inflowing current of electric osmose. (See Osmose, Electric.)

End Play.
The power to move horizontally in its bearings sometimes given to
armature shafts. This secures a more even wearing of the commutator
faces. End play is not permissible in disc armatures, as the attraction
of the field upon the face of the armature core would displace it
endwise. For such armatures thrust-bearings preventing end play have to
be provided.

The capacity for doing work. It is measured by work units which involve
the exercise of force along a path of some length. A foot-pound,
centimeter-gram, and centimeter-dyne are units of energy and work.

The absolute unit of energy is the erg, a force of one dyne exercised
over one centimeter of space. (See Dyne.)

The dimensions of energy are
  force (M * L / T^2) * space (L) = M * (L^2 / T^2).
Energy may be chemical (atomic or molecular), mechanical,
electrical, thermal, physical, potential, kinetic, or actual, and other
divisions could be formulated.


Energy, Atomic.
The potential energy due to atomic relations set free by atomic change;
a form of chemical energy, because chemistry refers to molecular as well
as to atomic changes. When atomic energy loses the potential form it
immediately manifests itself in some other form, such as heat or
electric energy. It may be considered as always being potential energy.
(See Energy, Chemical.)

[Transcriber's note: This item refers to chemical energy, that is
manifest in work done by electric forces during re-arrangement of
electrons. Atomic energy now refers to re-arrangement of  nucleons
(protons and neutrons) and the resulting conversion of mass into

Energy, Chemical.
A form of potential energy (see Energy, Potential) possessed by elements
in virtue of their power of combining with liberation of energy, as in
the combination of carbon with oxygen in a furnace; or by compounds in
virtue of their power of entering into other combinations more
satisfying to the affinities of their respective elements or to their
own molecular affinity. Thus in a galvanic couple water is decomposed
with absorption of energy, but its oxygen combines with zinc with
evolution of greater amount of energy, so that in a voltaic couple the
net result is the setting free of chemical energy, which is at once
converted into electrical energy in current form, if the battery is on a
closed circuit.

Energy, Conservation of.
A doctrine accepted as true that the sum of energy in the universe is
fixed and invariable. This precludes the possibility of perpetual
motion. Energy may be unavailable to man, and in the universe the
available energy is continually decreasing, but the total energy is the
same and never changes.

[Transcriber's note: If mass is counted a energy (E=m*(c^2)) then energy
is strictly conserved.]

Energy, Degradation of.
The reduction of energy to forms in which it cannot be utilized by man.
It involves the reduction of potential energy to kinetic energy, and the
reduction of kinetic energy of different degrees to energy of the same
degree. Thus when the whole universe shall have attained the same
temperature its energy will have become degraded or non-available. At
present in the sun we have a source of kinetic energy of high degree, in
coal a source of potential energy. The burning of all the coal will be
an example of the reduction of potential to kinetic energy, and the
cooling of the sun will illustrate the lowering in degree of kinetic
energy. (See Energy, Conservation of--Energy, Potential--Energy,

Energy, Electric.
The capacity for doing work possessed by electricity
under proper conditions. Electric energy may be either kinetic or
potential. As ordinary mechanical energy is a product of force and
space, so electric energy is a product of potential difference and
quantity. Thus a given number of coulombs of electricity in falling a
given number of volts develop electric energy. The dimensions are found
therefore by multiplying electric current intensity quantity
  ((M^.5) * (L^.5)),
by electric potential
  ((M^.5)*(L^1.5) / (T^2)),
giving (M * (L^2)/(T^2)),
the dimensions of energy in general as it should be.

The absolute unit of electric energy in electro-magnetic measure is
(1E-7) volt coulombs.


The practical unit is the volt-coulomb. As the volt is equal to 1E8
absolute units of potential and the coulomb to 0.1 absolute units of
quantity, the volt-coulomb is equal to 1E7 absolute units of energy.

The volt-coulomb is very seldom used, and the unit of Electric Activity
or Power (see Power, Electric), the volt-ampere, is universally used.
This unit is sometimes called the Watt, q. v., and it indicates the rate
of expenditure or of production of electric energy.

The storing up in a static accumulator or condenser of a given charge of
electricity, available for use with a given change of potential
represents potential electric energy.

The passing of a given quantity through a conductor with a given fall of
potential represents kinetic electric energy.

In a secondary battery there is no storage of energy, but the charging
current simply accumulates potential chemical energy in the battery,
which chemical energy is converted into electric energy in the discharge
or delivery of the battery.

It is customary to discuss Ohm's law in this connection; it is properly
treated under Electric Power, to which the reader is referred. (See
Power, Electric.)

[Transcriber's note: A volt-ampere or watt is a unit of power. A
volt-coulomb-second or watt-second is a unit of energy. Power multiplied by
time yields energy.]

Energy, Electric Transmission of.
If an electric current passes through a conductor all its energy is
expended in the full circuit. Part of the circuit may be an electrical
generator that supplies energy as fast as expended. Part of the circuit
may be a motor which absorbs part of the energy, the rest being expended
in forcing a current through the connecting wires and through the
generator. The electric energy in the generator and connecting wires is
uselessly expended by conversion into heat. That in the motor in great
part is utilized by conversion into mechanical energy which can do
useful work. This represents the transmission of energy. Every electric
current system represents this operation, but the term is usually
restricted to the transmission of comparatively large quantities of

A typical installation might be represented thus. At a waterfall a
turbine water wheel is established which drives a dynamo. From the
dynamo wires are carried to a distant factory, where a motor or several
motors are established, which receive current from the dynamo and drive
the machinery. The same current, if there is enough energy, may be used
for running lamps or electroplating. As electric energy (see Energy,
Electric,) is measured by the product of potential difference by
quantity, a very small wire will suffice for the transmission of a small
current at a high potential, giving a comparatively large quantity of
energy. It is calculated that the energy of Niagara Falls could be
transmitted through a circuit of iron telegraph wire a distance of over
1,000 miles, but a potential difference of 135,000,000 volts would be
required, something quite impossible to obtain or manage.

[Transcriber's note: Contemporary long distance power transmission lines
use 115,000 to 1,200,000 volts. At higher voltages corona discharges
(arcing) create unacceptable losses.]


Energy, Kinetic.
Energy due to matter being actually in motion. It is sometimes called
actual energy. The energy varies directly with the mass and with the
square of the velocity. It is represented in formula by .5 *M * (v^2).

Synonyms--Actual Energy--Energy of Motion--Dynamic Energy.

Energy, Mechanical.
The energy due to mechanical change or motion, virtually the same as
molar energy. (See Energy, Molar.)

Energy, Molar.
The energy of masses of matter due to movements of or positions of
matter in masses; such as the kinetic energy of a pound or of a ton in
motion, or the potential energy of a pound at an elevation of one
hundred feet.

Energy, Molecular.
The potential energy due to the relations of molecules and set free by
their change in the way of combination. It is potential for the same
reason that applies to atomic and chemical energy, of which latter it is
often a form, although it is often physical energy. The potential energy
stored up in vaporization is physical and molecular energy; the
potential energy stored up in uncombined potassium oxide and water, or
calcium oxide (quicklime) and water is molecular, and when either two
substances are brought together kinetic, thermal or heat energy is set
free, as in slaking lime for mortar.

Energy of an Electrified Body.
An electrified body implies the other two elements of a condenser. It is
the seat of energy set free when discharged. (See Dielectric, Energy
of.) The two oppositely charged bodies tend to approach. This tendency,
together with the distances separating them, represents a potential

Energy of Stress.
Potential energy due to stress, as the stretching of a spring. This is
hardly a form of potential energy. A stressed spring is merely in a
position to do work at the expense of its own thermal or kinetic energy
because it is cooled in doing work. If it possessed true potential
energy of stress it would not be so cooled.

Energy of Position.
Potential energy due to position, as the potential energy of a pound
weight raised ten feet (ten foot lbs.). (See Energy, Potential.)

Energy, Physical.
The potential energy stored up in physical position or set free in
physical change. Thus a vapor or gas absorbs energy in its vaporization,
which is potential energy, and appears as heat energy when the vapor


Energy, Potential, or Static Energy.
The capacity for doing work in a system due to advantage of position or
other cause, such as the stress of a spring. A pound weight supported
ten feet above a plane has ten foot lbs. of potential energy of position
referred to that plane. A given weight of an elementary substance
represents potential chemical energy, which will be liberated as actual
energy in its combination with some other element for which it has an
affinity. Thus a ton of coal represents a quantity of potential chemical
energy which appears in the kinetic form of thermal energy when the coal
is burning in a furnace. A charged Leyden jar represents a source of
potential electric energy, which becomes kinetic heat energy as the same
is discharged.

Energy, Thermal.
A form of kinetic molecular energy due to the molecular motion of bodies
caused by heat.

Non-available energy. As energy may in some way or other be generally
reduced to heat, it will be found that the equalizing of temperature,
actual and potential, in a system, while it leaves the total energy
unchanged, makes it all unavailable, because all work represents a fall
in degree of energy or a fall in temperature. But in a system such as
described no such fall could occur, therefore no work could be done. The
universe is obviously tending in that direction. On the earth the
exhaustion of coal is in the direction of degradation of its high
potential energy, so that the entropy of the universe tends to zero.
(See Energy, Degradation of.)

[Transcriber's note: Entropy (disorder) INCREASES, while AVAILABLE
ENERGY tends to zero.]

Entropy, Electric.
Clerk Maxwell thought it possible to recognize in the Peltier effect, q.
v., a change in entropy, a gain or loss according to whether the
thermo-electric junction was heated or cooled. This is termed Electric
Entropy. (See Energy, Degradation of.)



Epinus' Condenser.
Two circular brass plates, A and B, are mounted on insulating supports,
and arranged to be moved towards or away from each other as desired.
Between them is a plate of glass, C, or other dielectric. Pith balls may
be suspended back of each brass plate as shown. The apparatus is charged
by connecting one plate to an electric machine and the other to the
earth. The capacity of the plate connected to the machine is increased
by bringing near to it the grounded plate, by virtue of the principle of
bound charges. This apparatus is used to illustrate the principles of
the electric condenser. It was invented after the Leyden jar was


E. P. S.
Initials of Electrical Power Storage; applied to a type of secondary
battery made by a company bearing that title.



In electro-magnetic mechanism an arrangement for converting the pull of
the electro-magnet varying in intensity greatly over its range of
action, into a pull of sensibly equal strength throughout. The use of a
rocking lever acting as a cam, with leverage varying as the armature
approaches or recedes from the magnet core is one method of effecting
the result. Such is shown in the cut. E is an electro-magnet, with
armature a. A and B are the equalizer cams. The pull on the short end of
the cam B is sensibly equal for its whole length.

Many other methods have been devised, involving different shapes of pole
pieces, armatures or mechanical devices other than the one just shown.

Equipotential. adj.
Equal in potential; generally applied to surfaces. Thus every magnetic
field is assumed to be made up of lines of force and intersecting those
lines, surfaces, plane, or more or less curved in contour, can be
determined, over all parts of each one of which the magnetic intensity
will be identical. Each surface is the locus of equal intensity. The
same type of surface can be constructed for any field of force, such as
an electrostatic field, and is termed an equipotential surface.

Equipotential Surface, Electrostatic.
A surface in an electrostatic field of force, which is the locus of all
points of a given potential in such field; a surface cutting all the
lines of force at a point of identical potential. Lines of force are cut
perpendicularly by an equipotential surface, or are normal thereto.

Equipotential Surface, Magnetic and Electro-magnetic.
A surface bearing the same relation to a magnetic or electro-magnetic
field of force that an electrostatic equipotential surface (see
Equipotential Surface, Electrostatic,) does to an electrostatic field of

Equivalent, Chemical.
The quotient obtained by dividing the atomic weight of an element by its

Equivalents, Electro-chemical.
The weight of any substance set free by one coulomb of electricity. The
following give some equivalents expressed in milligrams:

Hydrogen            .0105    Mercury (mercurous)   2.10
Gold                .6877    Iron (ferric)          .1964
Silver             1.134     Iron (ferrous)         .294
Copper (cupric)     .3307    Nickel                 .3098
Mercury (mercuric) 1.05      Zinc                   .3413
Lead               1.0868    Chlorine               .3728
Oxygen              .89


Equivalent, Electro-mechanical.
The work or energy equivalent to unit quantities of electric energy, q.
v.; or equivalent to a unit current in a conductor whose ends differ one
unit of potential. The unit of electric energy taken is the watt-second
or volt-coulomb. One volt-coulomb is equal to
  Ergs                  1E7   [10000000]
  Foot Pound           .737337
  Gram-degree C.       .24068
  Horse Power Second   .0013406
  Pound-degree F.      .000955
  One horse power is equal to 745.943 volt coulombs per second.

Equivalent, Electro-thermal.
The heat produced by a unit current passing through a conductor with
unit difference of potential at its ends; the heat equivalent of a
volt-coulomb or watt-second. It is equal to
  Gram-degree C.   .24068
  Pound-degree F.  .000955

Equivalent, Thermo-chemical.
The calories evolved by the combination of one gram of any substance
with its equivalent of another substance being determined, the product
obtained by multiplying this number by the equivalent (atomic or
molecular weight / valency) of the first element or substance is the
thermo-chemical equivalent. If expressed in kilogram calories, the
product of the thermo-chemical equivalent by 0.43 gives the voltage
required to effect such decomposition.

The following are thermo-chemical equivalents of a few combinations:
  Water                34.5
  Zinc oxide           43.2
  Iron protoxide       34.5
  Iron Sesquioxide     31.9 X 3
  Copper oxide         19.2

"The mechanical energy of one volt electro-motive force exerted under
unit conditions through one equivalent of chemical action in grains."
(J. T. Sprague.) This unit is not in general use as the unit of electric
energy, the volt-coulomb and (for rate of electric energy) the
volt-ampere being always used.

The absolute or fundamental C. G. S. unit of work or energy. The work
done or energy expended in moving a body through one centimeter against
a resistance of one dyne.

Ten millions of ergs, or ten meg-ergs.

A term applied to leakage of current.

Etching, Electric.
A process of producing an etched plate. The plate is coated with wax,
and the design traced through as in common etching. It is then placed in
a bath and is connected to the positive terminal from a generator, whose
negative is immersed in the same bath, so that the metal is dissolved by
electrolytic action. By attaching to the other terminal and using a
plating bath, a rough relief plate may be secured, by deposition in the
lines of metal by electroplating.

Synonym--Electric Engraving.


The ether is a hypothetical thing that was invented to explain the
phenomena of light. Light is theoretically due to transverse vibrations
of the ether. Since the days of Young the conception of the ether has
extended, and now light, "radiant heat," and electricity are all treated
as phenomena of the ether. Electrical attraction and repulsion are
explained by considering them due to local stresses in the ether;
magnetic phenomena as due to local whirlpools therein. The ether was
originally called the luminiferous ether, but the adjective should now
be dropped. Its density is put at 936E-21 that of water, or equal to
that of the atmosphere at 210 miles above the earth's surface. Its
rigidity is about 1E-9 that of steel (see Ten, Powers of); as a whole it
is comparable to an all-pervading jelly, with almost perfect elasticity.
The most complete vacuum is filled with ether.

All this is a hypothesis, for the ether has never been proved to exist.
Whether gravitation will ever be explained by It remains to be seen.

[Transcriber's note: The Michelson-Morley experiment in 1887 (five years
before this book) cast serious doubt on the ether. In 1905 Einstein
explained electromagnetic phenomenon with photons. In 1963 Edward M.
Purcell used special relativity to derive the existence of magnetism and

A graduated glass tube for measuring the volumes of gases. In its
simplest form it is simply a cylindrical tube, with a scale etched or
engraved upon it, closed at one end and open at the other. The gas to be
measured is collected in it over a liquid, generally water, dilute
sulphuric acid in the gas voltameter, or mercury. Many different shapes
have been given them by Hoffmann, Ure, Bunsen and others.

Evaporation, Electric.
The superficial sublimation or evaporation of a substance under the
influence of negative electricity. It is one of the effects investigated
by Crookes in his experiments with high vacua. He found that when a
metal, even so infusible as platinum, was exposed to negative
electrification in one of his high vacuum tubes, that it was volatilized
perceptibly. A cadmium electrode heated and electrified negatively was
found to give a strong coating of metal on the walls of the tube. Even
in the open air the evaporation of water was found to be accelerated by
negative electrification.

Exchange, Telephone.
The office to which telephone wires lead in a general telephone system.
In the office by a multiple switch board, or other means, the different
telephones are interconnected by the office attendants, so that any
customers who desire it may be put into communication with each other.
The exchange is often termed the Central Office, although it may be only
a branch office.

Excitability, Faradic.
The action produced in nerve or muscle of the animal system by an
alternating or intermitting high potential discharge from an induction


Excitability, Galvanic.
The same as Faradic excitability, except that it refers to the effects
of the current from a galvanic battery.

Excitability of Animal System, Electric.
The susceptibility of a nerve or muscle to electric current shown by the
effect produced by its application.

A generator used for exciting the field magnet of a dynamo. In
alternating current dynamos, e. g., of the Westinghouse type, a special
dynamo is used simply to excite the field magnet. In central station
distribution the same is often done for direct current dynamos.

Exosmose, Electric.
The outflowing current of electric osmose. (See Osmose, Electric.)

Expansion, Coefficient of.
The number expressing the proportional increase in size, either length,
area or volume, of a substance under the influence generally of heat.
There are three sets of coefficients, (1) of linear expansion, (2) of
superficial expansion, (3) of cubic expansion or expansion of volume.
The first and third are the only ones much used. They vary for different
substances, and for the same substance at different temperatures. They
are usually expressed as decimals indicating the mixed number referred
to the length or volume of the body at the freezing point as unity.

Expansion, Electric.
(a) The increase in volume of a condenser, when charged
electrostatically. A Leyden jar expands when charged, and contracts when

(b) The increase in length of a bar of iron when magnetized.

This is more properly called magnetic expansion or magnetic elongation.

(a) A small magneto-generator for producing a current for heating the
wire in an electric fuse of the Abel type (see Fuse, Electric), and
thereby determining an explosion.

(b) The term may also be applied to a small frictional or influence
machine for producing a spark for exploding a spark fuse.

A coil, similar to a magnetizing coil (see Coil, Magnetizing), used for
investigating the electro-magnetic circuit and for similar purposes. If
placed around an electro-magnet and connected with a galvanometer, it
will produce a deflection, owing to a momentary induced current, upon
any change in the magnet, such as removing or replacing the armature. It
is useful in determining the leakage of lines of force and for general
investigations of that nature. It is often called an exploring coil.
Hughes' Induction Balance (see Induction Balance, Hughes') is sometimes
called a Magnetic Explorer. The exploring coil may be put in circuit
with a galvanometer for quantitative measurements or with a telephone
for qualitative ones.


Extension Bell Call.
A system of relay connection, q. v., by which a bell is made to continue
ringing after the current has ceased coming over the main line. It is
designed to prolong the alarm given by a magneto call bell, q. v., which
latter only rings as long as the magneto handle is turned. A vibrating
electric bell (see Bell, Electric,) is connected in circuit with a local
battery and a switch normally open, but so constructed as to close the
circuit when a current is passed and continue to do so indefinitely. The
distant circuit is connected to this switch. When the magneto is worked
it acts upon the switch, closes the local battery circuit and leaves it
closed, while the bell goes on ringing until the battery is exhausted or
the switch is opened by hand.

Eye, Electro-magnetic.
An apparatus used in exploring a field of electro-magnetic radiations.
It is a piece of copper wire 2 millimeters (.08 inch) in diameter, bent
into an almost complete circle 70 millimeters (.28 inch) in diameter,
with terminals separated by an air gap. This is moved about in the
region under examination, and by the production of a spark indicates the
locality of the loops or venters in systems of stationary waves.


Abbreviation for Fahrenheit, as 10º F., meaning 10º Fahrenheit. (See
Fahrenheit Scale.)

Fahrenheit Scale.
A thermometer scale in use in the United States and England. On this
scale the temperature of melting ice is 32°; that of condensing steam is
212°; the degrees are all of equal length. Its use is indicated by the
letter F., as 180° F. To convert its readings into centigrade, subtract
32 and multiply by 5/9. (b) To convert centigrade into F. multiply by
9/5 and add 32. Thus 180° F. = ((180-32) * 5/9)° C. = 82.2° C. Again
180° C. = (180 * 9/5) + 32 = 324° F.

[Transcribers note: 180° C. = (180 * 9/5) + 32 = 356° F. ]

The additions and subtractions must be algebraic in all cases. Thus when
the degrees are minus or below zero the rules for conversion might be
put thus: To convert degrees F. below zero into centigrade to the number
of degrees F. add 32, multiply by 5/9 and place a minus sign (-) before
it. (b) To convert degrees centigrade below zero into Fahrenheit,
multiply the number of degrees by 9/5, subtract from 32 if smaller; if
greater than 32 subtract 32 therefrom, and prefix a minus sign, thus:
-10° C. = 32 - (10 * 9/5) = 14°. Again, -30°C. = (30 * 9/5) - 32 = 22 =
-22° F.


The practical unit of electric capacity; the capacity of a conductor
which can retain one coulomb of electricity at a potential of one volt.

The quantity of electricity charged upon a conducting surface raises its
potential; therefore a conductor of one farad capacity can hold two
coulombs at two volts potential, and three coulombs at three volts, and
so on. The electric capacity of a conductor, therefore, is relative
compared to others as regards its charge, for the latter may be as great
as compatible with absence of sparking and disruptive discharge. In
other words, a one farad or two farad conductor may hold a great many
coulombs. Charging a conductor with electricity is comparable to pumping
air into a receiver. Such a vessel may hold one cubic foot of air at
atmospheric pressure and two at two atmospheres, and yet be of one cubic
foot capacity however much air is pumped into it.

The farad is equal to one fundamental electrostatic unit of capacity
multiplied by 9E11 and to one electro-magnetic unit multiplied by 1E-9.

The farad although one of the practical units is far too large, so the
micro-farad is used in its place. The capacity of a sphere the size of
the earth is only .000636 of a farad.

[Transcriber's note: Contemporary calculations give about .000720

Faraday, Effect.
The effect of rotation of its plane produced upon a polarized beam of
light by passage through a magnetic field. (See Magnetic Rotary

Faraday's Cube.
To determine the surface action of a charge, Faraday constructed a room,
twelve feet cube, insulated, and lined with tinfoil. This room he
charged to a high potential, but within it he could detect no excitement
whatever. The reason was because the electricity induced in the bodies
within the room was exactly equal to the charge of the room-surface, and
was bound exactly by it. The room is termed Faraday's cube.

Faraday's Dark Space.
A non-luminous space between the negative and positive glows, produced
in an incompletely exhausted tube through which a static discharge, as
from an induction coil, is produced. It is perceptible in a rarefaction
of 6 millimeters (.24 inch) and upwards. If the exhaustion is very high
a dark space appears between the negative electrode and its discharge.
This is known as Crookes' dark space.

Faraday's Disc.
A disc of any metal, mounted so as to be susceptible of rotation in a
magnetic field of force, with its axis parallel to the general direction
of the lines of force. A spring bears against its periphery and another
spring against its axle. When rotated, if the springs are connected by a
conductor, a current is established through the circuit including the
disc and conductor. The radius of the disc between the spring contacts
represents a conductor cutting lines of force and generating a potential
difference, producing a current. If a current is sent through the
motionless wheel from centre to periphery it rotates, illustrating the
doctrine of reversibility. As a motor it is called Barlow's or
Sturgeon's Wheel. If the disc without connections is rapidly rotated it
produces Foucault currents, q. v., within its mass, which resist its
rotation and heat the disc.


Fig. 168. "FARADAY'S NET."

Faraday's Net.
An apparatus for showing that the electric charge resides on the
surface. It consists of a net, conical in shape and rather deep, to
whose apex two threads, one on each side, are attached. Its mouth is
fastened to a vertical ring and the whole is mounted on an insulating

It is pulled out to its full extent and is electrified. No charge can be
detected inside it. By pulling one of the threads it is turned with the
other side out. Now all the charge is found on the outside just as
before, except that it is of course on the former inside surface of the
bag. The interior shows no charge.

Faraday's Transformer.
The first transformer. It was made by Michael Faraday. It was a ring of
soft iron 7/8 inch thick, and 6 inches in external diameter. It was
wound with bare wire, calico being used to prevent contact of the wire
with the ring and of the layers of wire with each other, while twine was
wound between the convolutions to prevent the wires from touching.
Seventy-two feet of copper wire, 1/20 inch diameter, were wound in three
superimposed coils, covering about one-half of the ring. On the other
half sixty feet of copper wire were wound in two superimposed coils.
Faraday connected his coils in different ways and used a galvanometer to
measure the current produced by making and breaking one of the circuits
used as a primary.

The coil is of historic interest.

Faraday's Voltameter.
A voltameter, in which the coulombs of current are measured by the
volume of the gas evolved from acidulated water. (See Voltameter, Gas.)

Faradic. adj.
Referring to induced currents, produced from induction coils. As Faraday
was the original investigator of the phenomena of electro-magnetic
induction, the secondary or induced electro-magnetic currents and their
phenomena and apparatus are often qualified by the adjective Faradic,
especially in electro-therapeutics. A series of alternating
electrostatic discharges, as from an influence machine (Holtz), are
sometimes called Franklinic currents. They are virtually Faradic, except
as regards their production.


Faradic Brush.
A brush for application of electricity to the person. It is connected as
one of the electrodes of an induction coil or magneto generator. For
bristles wire of nickel plated copper is generally employed.

In medical electricity the analogue of galvanization; the effects due to
secondary or induced currents; galvanization referring to currents from
a galvanic battery; also the process of application of such currents.

Sources of loss of current or of increased resistance or other troubles
in electric circuits.

A lead in an electric central station distribution system, which lead
runs from the station to some point in the district to supply current.
It is not used for any side connections, but runs direct to the point
where current is required, thus "feeding" the district directly. In the
two wire system a feeder may be positive or negative; in the three wire
system there is also a neutral feeder. Often the term feeder includes
the group of two or of three parallel lines.

Feeder Equalizer.
An adjustable resistance connected in circuit with a feeder at the
central station. The object of the feeder being to maintain a definite
potential difference at its termination, the resistance has to be varied
according to the current it is called on to carry.

Feeder, Main or Standard.
The main feeder of a district. The standard regulation of pressure
(potential difference between leads) in the district is often determined
by the pressure at the end of the feeder.

Feeder, Negative.
The lead or wire in a set of feeders, which is connected to the negative
terminal of the generator.

Feeder, Neutral.
In the three wire system the neutral wire in a set of feeders. It is
often made of less diameter than the positive and negative leads.

Feeder, Positive.
The lead or wire in a set of feeders, which wire is connected to the
positive terminal of the generator.

Ferranti Effect.
An effect as yet not definitely explained, observed in the mains of the
Deptford, Eng., alternating current plant. It is observed that the
potential difference between the members of a pair of mains rises or
increases with the distance the place of trial is from the station.

[Transcriber's note: This effect is due to the voltage drop across the
line inductance (due to charging current) being in phase with the
sending end voltages. Both capacitance and inductance are responsible
for producing this phenomenon.  The effect is more pronounced in
underground cables and with very light loads.]


Ferro-magnetic. adj.
Paramagnetic; possessing the magnetic polarity of iron.

Fibre and Spring Suspension.
A suspension of the galvanometer needle used in marine galvanometers.
The needle is supported at its centre of gravity by a vertically
stretched fibre attached at both its ends, but with a spring
intercalated between the needle and one section of the fibre.

Fibre Suspension.
Suspension, as of a galvanometer needle, by a vertical or hanging fibre
of silk or cocoon fibre, or a quartz fibre. (See Quartz.)

This suspension, while the most delicate and reliable known, is very
subject to disturbance and exacts accurate levelling of the instrument.

Fibre suspension is always characterized by a restitutive force. Pivot
suspension, q. v., on the other hand, has no such force.

Field, Air.
A field the lines of force of which pass through air; the position of a
field comprised within a volume of air.

Field, Alternating.
Polarity or direction being attributed to lines of force, if such
polarity is rapidly reversed, an alternating field results. Such field
may be of any kind, electro-magnetic or electrostatic. In one instance
the latter is of interest. It is supposed to be produced by high
frequency discharges of the secondary of an induction coil, existing in
the vicinity of the discharging terminals.

Field Density.
Field density or density of field is expressed in lines of force per
unit area of cross-section perpendicular to the lines of force.

Field, Distortion of.
The lines of force reaching from pole to pole of an excited field magnet
of a dynamo are normally symmetrical with respect to some axis and often
with respect to several. They go across from pole to pole, sometimes
bent out of their course by the armature core, but still symmetrical.
The presence of a mass of iron in the space between the pole pieces
concentrates the lines of force, but does not destroy the symmetry of
the field.

When the armature of the dynamo is rotated the field becomes distorted,
and the lines of force are bent out of their natural shape. The new
directions of the lines of force are a resultant of the lines of force
of the armature proper and of the field magnet. For when the dynamo is
started the armature itself becomes a magnet, and plays its part in
forming the field. Owing to the lead of the brushes the polarity of the
armature is not symmetrical with that of the field magnets. Hence the
compound field shows distortion. In the cut is shown diagrammatically
the distortion of field in a dynamo with a ring armature. The arrow
denotes the direction of rotation, and n n * * * and s s * * * indicate
points of north and south polarity respectively.


The distorted lines must be regarded as resultants of the two induced
polarities of the armature, one polarity due to the induction of the
field, the other to the induction from its own windings. The positions
of the brushes have much to do with determining the amount and degree of
distortion. In the case of the ring armature it will be seen that some
of the lines of force within the armature persist in their polarity and
direction, almost as induced by the armature windings alone, and leak
across without contributing their quota to the field. Two such lines are
shown in dotted lines.

In motors there is a similar but a reversed distortion.




Field, Drag of.
When a conductor is moved through a field so that a current is generated
in it, the field due to that current blends with the other field and
with its lines of force, distorting the field, thereby producing a drag
upon its own motion, because lines of force always tend to straighten
themselves, and the straightening would represent cessation of motion in
the conductor. This tendency to straightening therefore resists the
motion of the conductor and acts a drag upon it.

Field of Force.
The space in the neighborhood of an attracting or repelling mass or
system. Of electric fields of force there are two kinds, the
Electrostatic and the Magnetic Fields of Force, both of which may be
referred to. A field of force may be laid out as a collection of
elements termed Lines of Force, and this nomenclature is universally
adopted in electricity. The system of lines may be so constructed that
(a) the work done in passing from one equipotential surface to the next
is always the same; or (b) the lines of force are so laid out and
distributed that at a place in which unit force is exercised there is a
single line of force passing through the corresponding equipotential
surface in each unit of area of that surface. The latter is the
universal method in describing electric fields. It secures the following
advantages:--First: The potential at any point in the field of space
surrounding the attracting or repelling mass or masses is found by
determining on which imaginary equipotential surface that point lies.
Second: If unit length of a line of force cross n equipotential
surfaces, the mean force along that line along the course of that part
of it is equal to n units; for the difference of potential of the two
ends of that part of the line of force = n; it is also equal to F s (F
= force), because it represents numerically a certain amount of work;
but s = I, whence n = F. Third: The force at any part of the field
corresponds to the extent to which the lines of force are crowded
together; and thence it may be determined by the number of lines of
force which pass through a unit of area of the corresponding
equipotential surface, that area being so chosen as to comprise the
point in question. (Daniell.)

Field of Force, Electrostatic.
The field established by the attracting, repelling and stressing
influence of an electrostatically charged body. It is often termed an
Electrostatic Field. (See Field of Force.)


Field of Force of a Current.
A current establishes a field of force around itself, whose lines of
force form circles with their centres on the axis of the current. The
cut, Fig. 172, shows the relation of lines of force to current.




The existence of the field is easily shown by passing a conductor
vertically through a horizontal card. On causing a current to go through
the wire the field is formed, and iron filings dropped upon the card,
tend, when the latter is gently tapped, to take the form of circles. The
experiment gives a version of the well-known magnetic figures, q. v. See
Fig. 171.

The cut shows by the arrows the relation of directions of current to the
direction of the lines of force, both being assumptions, and merely
indicating certain fixed relations, corresponding exactly to the
relations expressed by the directions of electro-magnetic or magnetic
lines of force


Field, Pulsatory.
A field produced by pulsatory currents. By induction such field can
produce an alternating current.

Field, Rotating.
In a dynamo the field magnets are sometimes rotated instead of the
armature, the latter being stationary. In Mordey's alternator the
armature, nearly cylindrical, surrounds the field, and the latter
rotates within it, the arrangement being nearly the exact reverse of the
ordinary one. This produces a rotating field.

Field, Rotatory.
A magnetic field whose virtual poles keep rotating around its centre of
figure. If two alternating currents differing one quarter period in
phase are carried around four magnetizing coils placed and connected in
sets of two on the same diameter and at right angles to each other, the
polarity of the system will be a resultant of the combination of their
polarity, and the resultant poles will travel round and round in a
circle. In such a field, owing to eddy currents, masses of metal,
journaled like an armature, will rotate, with the speed of rotation of
the field.

Field, Stray.
The portion of a field of force outside of the regular circuit;
especially applied to the magnetic field of force of dynamos expressing
the portion which contributes nothing to the current generation.

Synonym--Waste Field.

Field, Uniform.
A field of force of uniform density. (See Field Density.)

Figure of Merit.
In the case of a galvanometer, a coefficient expressing its delicacy. It
is the reciprocal of the current required to deflect the needle through
one degree. By using the reciprocal the smaller the current required the
larger is the figure of merit. The same term may be applied to other

It is often defined as the resistance of a circuit through which one
Daniell's element will produce a deflection of one degree on the scale
of the instrument. The circuit includes a Daniell's cell of resistance
r, a rheostat R, galvanometer G and shunt S. Assume that with the shunt
in parallel a deflection of a divisions is obtained. The resistance of
the shunted galvanometer is (GS/G+S ; the multiplying power m of the
shunt is S+G/S; the formula or figure of merit is m d (r+R +G S/G+S).

The figure of merit is larger as the instrument is more sensitive.
Synonym--Formula of Merit.


A thin long piece of a solid substance. In general it is so thin as to
act almost like a thread, to be capable of standing considerable
flexure. The distinction between filament and rod has been of much
importance in some patent cases concerning incandescent lamps. As used
by electricians the term generally applies to the carbon filament of
incandescent lamps. This as now made has not necessarily any fibres, but
is entitled to the name of filament, partly by convention, partly by its
relative thinness and want of stiffness. (See Incandescent
Lamps--Magnetic Filament.)

Fire Alarm, Electric, Automatic.
A system of telegraph circuits, at intervals supplied with thermostats
or other apparatus affected by a change of temperature, which on being
heated closes the circuit and causes a bell to ring. (See Thermostat.)

Fire Alarm Telegraph System.
A system of telegraphic lines for communicating the approximate location
of a fire to a central station and thence to the separate fire-engine
houses in a city or district. It includes alarm boxes, distributed at
frequent intervals, locked, with the place where the key is kept
designated, or in some systems left unlocked. On opening the door of the
box and pulling the handle or otherwise operating the alarm, a
designated signal is sent to the central station. From this it is
telegraphed by apparatus worked by the central station operator to the
engine houses. The engines respond according to the discipline of the

Fire Cleansing.
Freeing the surface of an article to be plated from grease by heating.

Fire Extinguisher, Electric, Automatic.
A modification of the electric fire alarm (see Fire Alarm, Electric,
Automatic), in which the thermostats completing the circuits turn on
water which, escaping through the building, is supposed to reach and
extinguish a fire.

Flashing in a Dynamo or Magneto-electric Generator.
Bad adjustment of the brushes at the commutator, or other fault of
construction causes the production of voltaic arcs at the commutator of
a generator, to which the term flashing is applied.

Flashing of Incandescent Lamp Carbons.
A process of treatment for the filaments of incandescent lamps. The
chamber before sealing up is filled with a hydro-carbon vapor or gas,
such as the vapor of a very light naphtha (rhigolene). A current is then
passed through the filament heating it to redness. The more attenuated
parts or those of highest resistance are heated the highest, and
decompose most rapidly the hydro-carbon vapor, graphitic carbon being
deposited upon these parts, while hydrogen is set free. This goes on
until the filament is of uniform resistance throughout. It gives also a
way of making the resistance of the filament equal to any desired number
of ohms, provided it is originally of high enough resistance. The
process increases the conductivity of the filament.

After flashing the chambers are pumped out and sealed up.


Flashing Over.
A phenomenon observed in high potential dynamos. On a sudden alteration
of the resistance of the circuit a long blue spark will be drawn out
around the surface of the commutator from brush to brush. The spark is
somewhat of the nature of an arc, and may seriously injure commutators
whose sections are only separated by mica, or other thin insulation. In
the case of commutators whose sections are separated by air spaces it is
not so injurious.

In a commutator of a dynamo, the burning or wearing away of a commutator
segment to a lower level than the rest. Sometimes two adjacent bars will
be thus affected, causing a flat place on the commutator. It is not
always easy to account for the formation of flats. They may have their
origin in periodic vibrations due to bad mounting, or to sparking at the
particular point.

Floor Push.
A press or push button constructed to be set into the floor to be
operated by pressing with the foot. It is used to ring an alarm bell,
sound a buzzer or for similar service.

Fluid, Depolarizing.
A fluid used in voltaic batteries to dispose of the hydrogen, which goes
to the negative plate. This it does by oxidizing it. Chromic acid,
nitric acid, and chloric acids are among the constituents of liquid
depolarizers. (See Electropoion Fluid.)

Fluid, Electric.
The electric current and charge have sometimes been attributed to a
fluid. The theory, which never was much more than hypothetical, survives
to some extent in the single and double fluid theory. (See Single Fluid
Theory-Double Fluid Theory.)

The property of converting ether waves of one length, sometimes of
invisible length, into waves of another length (visible). AEsculin,
quinine salts, uranium glass and other substances exhibit this
phenomenon. The phenomenon is utilized in the production of Geissler

Flush Boxes.
A heavy iron box covered with a heavy hand plate and laid flush (whence
the name), or even with the surface of a roadway. Into it conductors of
an underground system lead, and it is used to make connections therewith
and for examining the leakage of the conductors and for similar
purposes. It is a "man-hole" (q. v.) in miniature.

An electric registering tide gauge or water level gauge.


Fly or Flyer, Electric.
A little wheel, ordinarily poised on a point, like a compass needle. It
carries several tangentially directed points, all pointing in the same
sense. When connected with a source of electricity of high potential it
revolves by reaction. The tension of its charge is highest at the
points, the air there is highly electrified and repelled, the reaction
pushing the wheel around like a Barker's mill or Hero's steam engine.
Sometimes the flyer is mounted with its axis horizontal and across the
rails on a railroad along which it travels.

Synonym--Reaction Wheel.

Foci Magnetic.
The two points on the earth's surface where the magnetic intensity is
greatest. They nearly coincide in position with the magnetic poles.

Fog, Electric.
Fogs occurring when the atmosphere is at unusually high potential and
accompanied by frequent change of such polarity.

Following Horns.
In dynamo-electric machines the projecting ends of the pole pieces
towards which the outer uncovered perimeter of the armature turns in its
regular operations. The leading horns are those away from which the
armature rotates. In considering rotation the exposed portion of the
superficies of the armature is considered. The definition would have to
be reversed if the part facing the pole pieces were considered.

Synonym--Trailing Horns.

A unit of illuminating power; the light given by one standard candle at
a distance of one foot. The ordinary units of illuminating power are
entirely relative; this is definite. It is due to Carl Herring.

A practical unit of work or energy. The quantity of work required to
raise a pound one foot, or one hundred pounds one-hundredth of a foot,
and so on; or the potential energy represented by a weight at an
elevation under these conditions.

In a dynamo with armature at the lower end of its field magnets, the
plate generally of zinc, interposed between it and the iron base plate
to prevent the leakage of lines of force outside of the circuit. Any
diamagnetic material which is mechanically suitable may be used.

Force may be variously defined.
(a) Any cause of change of the condition of matter with respect to
motion or rest.

(b) A measurable action upon a body under which the state of rest of
that body, or its state of uniform motion in a straight line, suffers

(c) It may be defined by its measurement as the rate of change of
momentum, or

(d) as the rate at which work is done per unit of space traversed.

Force is measured by the acceleration or change of motion it can impart
to a body of unit mass in a unit of time, or, calling
force, F,
mass, m
acceleration per second a
we have F = m a.

The dimensions of force are
mass (M) * acceleration (L/(T^2)) = (M*L)/(T^2).


Force de Cheval. Horse power (French).
It is the French or metric horse power.
It is equal to:
  542.496    Foot lbs. per second.
     .9864   English Horse Power.
   75.0      Kilogram-meters per second.

Force, Electro-magnetic.
The mechanical force of attraction or repulsion acting on the
electro-magnetic unit of quantity. Its intensity varies with the square
of the distance. It may also be defined as electric force in the
electro-magnetic system.

Its dimensions are equal to
mechanical force ((M*L)/(T^2)) divided by quantity ((M^.5)*(L^.5))
= ((M^.5)*(L^.5))/(T^2).

Force, Electrostatic.
The force by which electric matter or electrified surfaces attract or
repel each other. It is also termed electric force (not good) and
electro-motive intensity. It is the mechanical force acting upon a unit
quantity of electricity. Its intensity varies with the square of the

Its dimensions are therefore equal to
(quantity * unity / (square of distance) Q. * 1 / (L^2)
 = ((M^.5) * (L^1.5) )/ T*1 / (L^2)
 = ((M^.5) * (L^.5)) / T
These dimensions are also those of potential difference.

[Transcriber's Note: The image of the preceding paragraph is included
for "clarity".]

The objection to the term electric force is that it may be applied also
to electro-magnetic force, and hence be a source of confusion.

Forces, Parallelogram of.
The usual method of composing forces or resolving a force. The sides of
a parallelogram of forces represent component forces and the diagonal
represents the resultant. See Component--Resultant--Forces, Composition
of--Forces, Resolution of.

Forces, Composition of.
When several forces act in a different direction upon a point they may
be drawn or graphically represented as arrows or lines emanating from
the point in the proper direction and of lengths proportional to the
force they exercise. Any two can be treated as contiguous sides of a
parallelogram and the parallelogram can be completed. Then its diagonal,
called the resultant, will represent the combined action of the two
forces, both as regards direction and intensity. This is the composition
of two forces.

If more than two forces act upon the given point the resultant can be
composed with any of the others and a new force developed. The new
resultant can be combined with another force, and the process kept up,
eliminating the components one by one until a final resultant of all is
obtained. This will give the exact direction and intensity of the
forces, however many or varied.


Forces, Resolution of.
The developing from a single force treated as a resultant, two other
forces in any desired direction. The reverse of composition of forces.
(See Forces, Composition of--Forces, Parallelogram

Force, Tubes of.
Aggregations of lines of force, either electrostatic or magnetic. They
generally have a truncated, conical or pyramidal shape and are not
hollow. Every cross-section contains the same number of lines. The name
it will seem is not very expressive.

Force, Unit of.
The fundamental or C. G. S. unit or force is the dyne, q. v.

The British unit of force is the poundal (the force which will produce
an acceleration of one foot per second in a mass of one pound). It is
equal to about 10/322 pound. A force cannot be expressed accurately in
weight units, because weight varies with the latitude.

The process of producing secondary battery plates from lead plates by
alternately passing a charging current through the cell and then
allowing it to discharge itself and repeating the operation. (See
Battery, Secondary, Planté's.)

Foundation Ring.
In a dynamo armature the ring-shaped core on which Gramme ring armatures
and other ring armatures are wound.

Fourth State of Matter.
Gas so rarefied that its molecules do not collide, or rarely do so;
radiant matter, q. v.

[Transcriber's note: This term now refers to plasma, an ionized gas,
which contains free electrons. The ions and electrons move somewhat
independently making plasma electrically conductive. It responds
strongly to electromagnetic fields.]

In a dynamo the bed-piece is sometimes called the frame.

Franklin's Experiment.
Franklin proved the identity of lightning and electricity by flying a
kite in a thunder storm. The kite was of silk so as to endure the
wetting. When the string became wet sparks could be taken from a key
attached to its end. The main string was of hemp; at the lower end was a
length of silk to insulate it. The key was attached near the end of and
to the hemp string.

Franklin's Plate.
A simple form of condenser. It consists of a plate of glass coated on
each side with tinfoil with a margin of about an inch of clear glass.
One coating may be grounded as indicated in the cut, and the plate
charged like a Leyden jar. Or one side may be connected with one
terminal, and the other with the other terminal of an influence machine
and the pane will be thus charged.

Synonym--Fulminating Pane.



Franklin's Theory.
The single fluid theory, q. v., of electricity.

The number of double reversals or complete alternations per second in an
alternating current.


Frictional Electricity.
Electricity produced by friction of dissimilar substances. (See
Electrostatic Series.) The contact theory holds that friction plays only
a secondary rôle in this process; that it increases the thoroughness of
contact, and tends to dry the rubbing surfaces, but that the charges
induced are due to contact of dissimilar substances, not to friction of
one against the other.

Frictional Heating.
The heating of a conductor by the passage of a current; the Joule
effect, q. v.

The outlying edge of a magnetic field.

Frog, Galvani's Experiment With.
A classic experiment in electricity, leading to the discovery of current
or dynamic electricity. If a pair of legs of a recently killed frog are
prepared with the lumbar nerves exposed near the base of the spinal
column, and if a metallic conductor, one half-length zinc and the other
half-length copper, is held, one end between the lumbar nerves and the
spine, and the other end against one of the muscles of the thigh or
lower legs, the moment contact occurs and the circuit is completed
through the animal substance the muscles contract and the leg is
violently drawn upwards. Galvani, in 1786, first performed, by accident,
this famous experiment, it is said, with a scalpel with which he was
dissecting the animal. He gave his attention to the nerves and muscles.
Volta, more happily, gave his attention to the metals and invented the
voltaic battery, described by him in a letter to Sir Joseph Banks, dated

Frog, Rheoscopic.
If the nerve or living muscle of a frog is suddenly dropped upon another
living muscle so as to come in contact with its longitudinal and
transverse sections, the first muscle will contract on account of the
stimulation of its nerve due to the passage of a current derived from
the second muscle (Ganot). The experiment goes under the above title.


A term applied to a noise sometimes produced in a voltaic arc due to too
close approach of the carbons to each other. It has been suggested that
it may be due to volatilization of the carbon. (Elihu Thomson.)

An irregular and tubular mass of vitrified quartz, believed to be formed
by melting under the lightning stroke.


Furnace, Electric.
A furnace in which the heat is produced by the electric current. It has
hitherto been practically used only in the extraction of aluminum and
silicium  from their ores. The general principle involves the formation
of an arc between carbon electrodes. The substances to be treated are
exposed to the heat thus produced. Sometimes the substances in the arc
form imperfect conductors, and incandescence takes a part in the action.
Sometimes the substances are merely dropped through the arc.

[Transcriber's note: Silicium is silicon.]

Fuse Board.
A tablet on which a number of safety fuses are mounted. Slate is
excellent material for the tablet, as it is incombustible, and is easily
drilled and worked.

Fuse Box.
A box containing a safety fuse. Porcelain is an excellent material for
its base. No combustible material should enter into its composition.

Fuse, Cockburn.
A safety fuse or cut off which consists of a wire of pure tin running
from terminal to terminal, to whose centre a leaden ball is secured by
being cast into position. The connection with the terminals is made by
rings at the ends of the wire through which the terminal screws are
passed and screwed home. When the tin softens under too heavy a current
the weight of the shot pulls it apart.




Fuse, Electric.
A fuse for igniting an explosive by electricity. There are two kinds. In
one a thin wire unites the ends of the two conducting wires as they
enter the case of the fuse. The larger wires are secured to the case, so
that no strain comes on the fine wire. On passing a current of
sufficient strength the small wire is heated. In use the fuse is bedded
in powder, which again may be surrounded by fulminating powder, all
contained in a copper or other metallic case. Such a detonator is used
for exploding guncotton and other high explosives.

The other kind of fuse is similar, but has no thin connecting wire. The
ends of the conductors are brought nearer together without touching. In
use a static discharge is produced across from end to end of the
conductors, igniting a proper explosive placed there as in the other

The first kind of fuse is generally operated by a battery or small
mechanical generator--the latter by a spark coil, frictional or
influence machine or by a Leyden jar.


Galvanic. adj.
Voltaic; relating to current electricity or the electrolytic and
electro-chemical relations of metals. (For titles in general under this
head see Voltaic--or the main title.)

Galvanic Element.
A galvanic couple with exciting fluid and adjuncts; a galvanic cell. The
word element is sometimes applied to the electrodes of a cell, as the
carbon element or zinc element.


Galvanic Polarization.
The polarization of a voltaic couple. (See Polarization.)

The science of voltaic or current electricity.

(a) Electroplating or depositing a metal over the surface of another by

(b) In medical electricity the effects produced on any part of the
system by the current of voltaic battery. Various descriptive
qualifications are prefixed, such as "general" galvanization, indicating
its application as applied to the whole body, "local" for the reverse
case, and so on.

Galvanization, Labile.
Application of the galvanic current in electro-therapeutics where one
sponge electrode is employed which is rubbed or moved over the body, the
other being in constant contact with the body.

Galvanized Iron.
Iron coated with zinc by cleaning and immersion in melted zinc. The iron
is prevented from rusting by galvanic action. It forms the negative
element in a couple of which the zinc is the positive element. From this
electric protective action the name is derived.

Galvano-cautery, Chemical.
Electro-therapeutic treatment with sharp electrodes, one of which is
inserted in the tissue and a current passed by completing the circuit
through the tissue so as to electrolyze or decompose the fluids of the
tissue. It is applied in the removal of hair or extirpation of the
follicle. The process is not one of heating, and is improperly named

In medical electricity the application of the voltaic and induced or
secondary current simultaneously to any part of the system.

An instrument for measuring current strength and sometimes for measuring
inferentially potential difference, depending on the action of a
magnetic field established by the current, such action being exerted on
a magnetic needle or its equivalent.

A current passing through a conductor establishes circular lines of
force. A magnetic needle placed in their field is acted on and tends to
place itself parallel with the lines, in accordance with the principles
of current induction. (See Induction, Electro-magnetic.) A common
compass held near a conductor through which a current is passing tends
to place itself at right angles to such conductor. For a maximum effect
the conductor or the part nearest the needle should lie in the magnetic
meridian. If at right angles thereto its action will only strengthen the
directive force of the earth's induction or magnetic field, as the
needle naturally points north and south. Such combination is virtually a


A typical galvanometer comprises a flat coil of wire placed horizontally
within which a magnetic needle is delicately poised, so as to be free to
rotate with the least possible friction. The needle may be supported on
a sharp point like a compass needle, or may be suspended by a long fine
filament. It should be covered by a glass plate and box, or by a glass
shade. Finally a graduated disc may be arranged to show the amount of
deflection of the needle.

In use the apparatus is turned about until the needle, as acted on by
the earth's magnetic field, lies parallel to the direction of the coils
of wire. On passing a current through the coil the needle is deflected,
more or less, according to its strength.

By using exceedingly fine wire, long enough to give high resistance, the
instrument can be used for very high potentials, or is in condition for
use in determining voltage. By using a coil of large wire and low
resistance it can be employed in determining amperage. In either case
the deflection is produced by the current.

The needle is often placed above or below the coil so as only to receive
a portion of its effect, enough for all practical purposes in the
commoner class of instruments.

The galvanometer was invented by Schweigger a short time after Oersted's
discovery, q. v.

Galvanometer, Absolute.
A galvanometer giving absolute readings; properly one whose law of
calibration can be deduced from its construction. Thus the diameter of
the coil, and the constants and position of a magnetic needle suspended
in its field being known, the current intensity required to deflect the
needle a given number of degrees could be calculated.

Galvanometer, Aperiodic.
A galvanometer whose needle is damped (see Damping) as, for instance, by
the proximity of a plate of metal, by an air vane or otherwise, so that
it reaches its reading with hardly any oscillation. A very light needle
and a strong magnetic field also conduce to vibrations of short period
dying out very quickly. Such galvanometers are termed "dead-beat." No
instrument is absolutely dead-beat, only relatively so.



Galvanometer, Astatic.
A galvanometer with a pair of magnetic needles connected astatically, or
parallel with their poles in opposition. (See Astatic Needle.) Each
needle has its own coil, the coils being wound in opposite directions so
as to unite in producing deflections in the same sense. As there should
be some directive tendency this is obtained by one of the magnets being
slightly stronger than the other or by the proximity of a fixed and
adjustable controlling magnet, placed nearer one needle than the other.

For small deflections the currents producing them are proportional to
their extent.

Galvanometer, Ballistic.
A galvanometer whose deflected element has considerable moment of
inertia; the exact opposite of an aperiodic or dead beat galvanometer.
(See Galvanometer, Aperiodic.) All damping by air vanes or otherwise
must be carefully done away with.


Siemens & Halske's galvanometer is of the reflecting or mirror type (see
Galvanometer, Reflecting) with suspended, bell-shaped magnet, in place
of the ordinary magnetic needle, or astatic combination of the lightest
possible weight in the regular instrument. A copper ball drilled out to
admit the magnet is used as damper in the ordinary use of the
instrument. To convert it into a ballistic galvanometer the copper ball
is removed. The heavy suspended magnet then by its inertia introduces
the desired element into the instrument.


Referring to the cut, Fig. 179, M is the suspended magnet, with north
and south poles n and s; S is the reflecting mirror; r is the tube
containing the suspending thread; R is the damper removed for ballistic

The ballistic galvanometer is used to measure quantities of electricity
in an instantaneous discharge, which discharge should be completed
before the heavy needle begins to move. The extreme elongation or throw
of the needle is observed, and depends (1) on the number of coulombs (K)
that pass during the discharge; (2) on the moment of inertia of the
needle and attached parts; (3) on the moment of the controlling forces,
i. e., the forces tending to pull the needle back to zero; (4) on the
moment of the damping forces; (5) on the moment of the deflecting forces
due to a given constant current. The formula is thus expressed:

K = (P / PI ) * A * sin( kº / 2 ) / tan( aº )

in which K = coulombs discharged; P = periodic time of vibration of
needle; A = amperes producing a steady deflection equal to  aº  ; kº =
first angular deflection of needle. For accuracy kº and aº should both
be small and the damping so slight as to be negligible. Otherwise a
correction for the latter must be applied. For approximate work for kº
and aº the deflections read on the scale may be used with the following

K = (P / PI ) * ( A / 2 ) * ( kº / aº )

Galvanometer Constant.
Assume a galvanometer with a very short needle and so placed with
respect to its coils that the magnetic field produced by a current
circulating in them is sensibly uniform in the neighborhood of the
needle, with its lines of force at right angles thereto. The field is
proportional to the current i, so that it may be denoted by G i. Then G
is the galvanometer constant. If now the angle of deflection of the
needle is ? against the earth's field H, M being the magnetic moment of
the needle we have G i M cos ? = H M sin ? or i = (H/G)* tan ?. H/G is
the reduction factor; variable as H varies for different places.

For a tangent galvanometer the constant G is equal to  2*PI*(n/a), in
which n denotes the number of turns of wire, and a denotes the radius of
the circle.

Galvanometer, Differential.
A galvanometer in which the needle is acted on by two coils wound in
opposition, each of equal deflecting action and of equal resistance. If
a current is divided between two branches or parallel conductors, each
including one of the coils, when the needle points to zero the
resistances of the two branches will bc equal. In the cut, C C'
represent the coils, and A and B the two leads into which the circuit, P
Q, is divided.




Galvanometer, Direct Reading.
A calibrated galvanometer, whose scale is graduated by volts or amperes,
instead of degrees.

Galvanometer, Marine. (Sir William Thomson's.)
A galvanometer of the reflecting type, for use on shipboard. A fibre
suspension is adopted for the needle. The fibre is attached to a fixed
support at one end and to a spring at the other, and the needle is
suspended by its centre of gravity. This secures it to a considerable
extent from disturbance due to the rolling of the ship. A thick iron box
encloses the needle, etc., to cut off any magnetic action from the ship.
(See Galvanometer, Reflecting.)

Galvanometer, Potential.
A galvanometer wound with fine German silver wire to secure high
resistance used for determination of potential difference.

Galvanometer, Proportional.
A galvanometer so constructed that the deflections of its index are
proportional to the current passing. It is made by causing the
deflecting force to increase as the needle is deflected, more and more,
or by causing the restitutive force to diminish under like conditions,
or by both. The condition is obtained in some cases by the shape and
position of the deflecting coils.

Galvanometer, Quantity.
A galvanometer for determining quantities of electricity, by the
deflections produced by discharging the quantities through their coils.
It is a ballistic galvanometer with very little or no damping.




Galvanometer, Reflecting.
A galvanometer the deflections of whose needle are read by an image
projected by light reflected from a mirror attached to the needle or to
a vertical wire carrying the needle. A lamp is placed in front of the
instrument facing the mirror. The light of the lamp is reflected by the
mirror upon a horizontal scale above the lamp. An image of a slit or of
a wire may be caused thus to fall upon the scale, the mirror being
slightly convex, or a lens being used to produce the projection.


If the mirror swings through a horizontal arc, the reflected image will
move, in virtue of a simple geometrical principle, through an arc of
twice as many degrees. The scale can be placed far from the mirror, so
that the ray of light will represent a weightless index of very great
length, and minute deflections of the needle will be shown distinctly
upon the scale.

In the cut, Fig. 182, the ray of light from the lamp passes through the
aperture, m m, and is made parallel by the lens, L. At s is the mirror
attached to the needle and moving with it. A scale placed at t receives
the reflection from the mirror. The cut, Fig. 183, shows one form of the
instrument set up for use.

Synonym--Mirror Galvanometer.

Galvanometer Shunt.
To prevent too much current passing through a galvanometer (for fear of
injury to its insulation) a shunt is sometimes placed in parallel with
it. The total current will be distributed between galvanometer and shunt
in the inverse ratio of their respective resistances. (See Multiplying
Power of a Shunt.)



Galvanometer, Sine.
A galvanometer whose measurements depend upon the sine of the angle of
deflection produced when the coil and needle lie in the same vertical

The needle, which may be a long one, is surrounded by a coil, which can
be rotated about a vertical axis passing through the point of suspension
of the needle. Starting with the needle at rest in the plane of the
coil, a current is passed through the coil deflecting the needle, the
coil is swung around deflecting the needle still more, until the needle
lies in the plane of the coil; the intensity of the current will then be
in proportion to the sine of the angle through which the coil and needle

In the galvanometer M is a circle carrying the coil, N is a scale over
which the needles, m and n, move, the former being a magnetic needle,
the latter an index at right angles and attached thereto; a and b are
wires carrying the current to be measured. The circles, M and N, are
carried by a base, O, around which they rotate. H is a fixed horizontal
graduated circle. In use the circle, M, is placed in the magnetic
meridian, the current is passed through the coil, M; the needle is
deflected; M is turned until its plane coincides with the direction of
the needle, m. The current strength is proportional to the sine of the
angle of deflection. This angle is measured by the vernier, C, on the
circle, H. The knob, A, is used to turn the circle, M.



Galvanometer, Tangent.
A galvanometer in which the tangents of the angles of deflection are
proportional to the currents producing such deflections.

For this law to apply the instrument in general must fulfill the
following conditions:

(1) The needle must be controlled by a uniform magnetic field such as
that of the earth;

(2) the diameter of the coil must be large compared to the length of the

(3) the centre of suspension of the needle must be at the centre of the

(4) the magnetic axis of the needle must lie in the plane of the coil
when no current is passing.

If a single current strength is to be measured the best results will be
attained when the deflection is 45°; in comparing two currents the best
results will be attained when the deflections as nearly as possible are
at equal distances on both sides of 45°.

The needle should not exceed in length one-tenth the diameter of the

For very small deflections any galvanometer follows the law of
tangential deflection.

As for very small deflections the tangents are practically equal to the
arcs subtended, for such deflections the currents are proportional to
the deflections they produce.

The sensibility is directly proportional to the number of convolutions
of wire and inversely proportional to their diameter.

The tangent law is most accurately fulfilled when the depth of the coil
in the radial direction is to the breadth in the axial direction as
squareRoot(3):squareRoot(2), or about as 11:9.

Galvanometer, Torsion.
A galvanometer whose needle is suspended by a long filament or by a
thread and spiral spring against whose force of torsion the movements of
the needle are produced. The current strength is determined by bringing
the needle back to its position of rest by turning a hand-button or
other arrangement. The angle through which this is turned gives the
angle of torsion. From this the current strength is calculated on the
general basis that it is proportional to the angle of torsion.



Galvanometer, Vertical.
A galvanometer whose needle is mounted on a horizontal axis and is
deflected in a vertical plane. One of the poles is weighted to keep it
normally vertical, representing the control. It is not used for accurate

Synonym--Upright Galvanometer.


Galvanometer, Volt- and Ampere-meter.
A galvanometer of Sir William Thomson's invention embodying the tangent
principle, and having its sensibility adjustable by moving the magnetic
needle horizontally along a scale (the "meter") towards or away from the
coil. A curved magnet is used to adjust the control. The leads are
twisted to prevent induction.

The instrument is made with a high resistance coil for voltage
determinations, and with a low resistance coil for amperage

At one end of a long base board a vertical coil with its plane at right
angles to the axis of the board is mounted. A scale (the "meter" of the
name) runs down the centre of the board. A groove also runs down the
centre. The magnetic needle is contained in a quadrant-shaped
glass-covered box which slides up and down the groove. A number of short
parallel needles mounted together, with an aluminum pointer are used.



In the cut P is the base board, M is a glass covered case containing the
magnetic needle, and sliding along the base board, being guided by the
central groove, C, is the coil. Between the coil and the needle is the
arched or bent controlling magnet. The long twisted connecting wires are
seen on the right hand.

The deposition of metals by electrolysis, a disused term replaced
by electro-deposition, electroplating, and electro-metallurgy.

An operation in medical electricity. (See Electro-puncture.)

An instrument, generally of the galvanometer type, used for ascertaining
whether a current is flowing or not. Any galvanoscope, when calibrated,
if susceptible thereof, becomes a galvanometer.

Gas, Electrolytic.
Gas produced by the decomposition, generally of water, by electrolysis.
It may be hydrogen or oxygen, or a mixture of the two, according to how
it is collected. (See Gases, Mixed.)

Gases, Mixed.
The mixture of approximately one volume of oxygen and two volumes of
hydrogen collected in the eudiometer of a gas voltameter or other
electrolytic apparatus.

The evolution of gas from the plates of a storage battery in the
charging process, due to too high voltage in the circuit of the charging

An apparatus for illuminating by an incandescent lamp the interior of
the stomach, and with prisms to refract the rays of light so that the
part can be seen. The stomach is inflated with air, if desirable, to
give a better view. An incandescent platinum spiral in a water jacket
has been employed for the illumination.

Gassiot's Cascade.
A goblet lined for half its interior surface with tinfoil. It is placed
in the receiver of an air pump from the top of whose bell a conductor
descends into it, not touching the foil. On producing a good
rarefaction, and discharging high tension electricity from between the
conductor just mentioned and the metal of the machine, a luminous effect
is produced, as if the electricity, pale blue in color, was overflowing
the goblet.

A name suggested for unit intensity of magnetic field. Sylvanus P.
Thomson proposed for its value the intensity of a field of 1E8 C. G. S.
electro-magnetic units. J. A. Fleming proposed the strength of field
which would develop one volt potential difference in a wire 1E6
centimeters long, moving through such field with a velocity of one
centimeter per second. This is one hundred times greater than Thomson's
standard. Sir William Thomson suggested the intensity of field produced
by a current of one ampere at a distance of one centimeter

The gauss is not used to any extent; practical calculations are based on
electro-magnetic lines of force.


Gauss' Principle.
An electric circuit acts upon a magnetic pole in such a way as to make
the number of lines of force that pass through the circuit a maximum.


Gauss, Tangent Positions of.
The "end on" and "broadside" methods of determining magnetization
involve positions which have been thus termed. (See Broadside Method and
End on Method.)

Gear, Magnetic Friction.
Friction gear in which the component wheels are pressed against each
other by electromagnetic action. In the cut, repeated from Adherence,
Electro-magnetic, the magnetizing coil makes the wheels, which are of
iron, press strongly together.



Geissler Tubes.
Sealed tubes of glass containing highly rarefied gases, and provided
with platinum electrodes extending through the glass tightly sealed as
they pass through it, and often extending a short distance beyond its
interior surface.

On passing through them the static discharge luminous effects are
produced varying with the degree of exhaustion, the contents (gas), the
glass itself, or solutions surrounding it. The two latter conditions
involve fluorescence phenomena often of a very beautiful description.

The pressure of the gas is less than one-half of a millimeter of
mercury. If a complete vacuum is produced the discharge will not pass.
If too high rarefaction is produced radiant matter phenomena (see
Radiant State) occur.

Geissler tubes have been used for lighting purposes as in mines, or for
illuminating the interior cavities of the body in surgical or medical

Generating Plate.
The positive plate in a voltaic couple, or the plate which is dissolved;
generally a plate of zinc.

Synonyms--Positive Plate--Positive Element.

Generator, Current.
Any apparatus for maintaining an electric current. It may be as regards
the form of energy it converts into electrical energy, mechanical, as a
magneto or dynamo electric machine or generator; thermal, as a
thermo-electric battery; or chemical, as a voltaic battery; all of which
may be consulted.

Generator, Secondary.
A secondary or storage battery. (See Battery, Secondary.)

German Silver.
An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to
its high resistance and moderate cost and small variation in resistance
with change of temperature, it is much used for resistances. From Dr.
Mathiessen's experiment the following constants are deduced in legal
  Relative Resistance (Silver = 1),      13.92
  Specific Resistance at 0° C. (32F.),   20.93 microhms.
  Resistance of a wire,
  (a) 1 foot long, weighing 1 grain,      2.622   ohms.
  1 foot long, 1/1000 inch thick,       125.91     "
  1 meter long, weighing 1 gram,          1.830    "
  1 meter long, 1 millimeter thick,       0.2666   "
  Resistance of a 1 inch cube at 0°C. (32° F.),   8.240 microhms.

Approximate percentage increase of resistance per 1° C. (1.8° F.) at
about 20° C. (68° F.), 0.044 per cent.

Gilding, Electro-.
The deposition of gold by an electric current, or electrolytically in
the electroplating bath.

Gilding Metal.
A special kind of brass, with a high percentage of copper, used to make
objects which are to be gilded by electrolysis.


A suspension used for ships' compasses and sometimes for other
apparatus. It consists of a ring held by two journals, so as to bc free
to swing in one plane. The compass is swung upon this ring, being placed
concentrically therewith. Its journals are at right angles to those of
the ring. This gives a universal joint by which the compass, weighted
below its line of support, is always kept horizontal.


A fused mixture of silicates of various oxides. It is of extremely
varied composition and its electric constants vary greatly. Many
determinations of its specific resistance have been made. For flint
glass at 100° C. (212° F.) about (2.06E14) ohms --at 60° C (140° F.)
(1.020E15) (Thomas Gray) is given, while another observer (Beetz) gives
for glass at ordinary temperatures an immeasurably high resistance. It
is therefore a non-conductor of very high order if dry. As a dielectric
the specific inductive capacity of different samples of flint glass is
given as 6.57--6.85--7.4--10.1 (Hopkinson), thus exceeding all other
ordinary dielectrics. The densest glass, other things being equal, has
the highest specific inductive capacity.

A metal, one of the elements; symbol Au. c .; atomic weight, 196.8;
equivalent, 65.6; valency, 3; specific gravity 19.5.
It is a conductor of electricity.

                                            Annealed.   Hard drawn.
Relative Resistance (Annealed Silver = 1),   1.369       1.393
Specific Resistance,                         2.058       2.094
Resistance of a wire at 0° C. (32°F.)
(a) 1 foot long, weighing 1 grain,          57.85     58.84   ohms
(b) 1 foot long, 1/1000 inch thick,         12.38     12.60    "
(c) 1 meter long, weighing 1 gram,            .4035     .4104  "
(d) 1 meter long, 1 millimeter thick,         .02620    .02668 "
Resistance of a 1 inch cube at 0° C.(32° F.)  .8102     .8247

Approximate increase in resistance per 0° C., (1.8° F)
at about 20° C. (68° F.), 0.365 per cent.

Electro-chemical equivalent (Hydrogen = .0105), .6888


Gold Bath.
A solution of gold used for depositing the metal in the electroplating

A great number of formulae have been devised, of which a few
representative ones are given here.
                            COLD BATHS.            HOT BATHS.
Water,               10,000  10,000  10,000  10,000   5,000  3,000
Potassium Cyanide,      200      --     200      10      --     50
Gold,                   100      15     100      10      10     10
Potassium Ferrocyanide,  --     200      --      --     150     --
Potassium Carbonate,     --     150      --      --      50     --
Ammonium Chloride,       --      30      --      --      20     --
Aqua Ammoniae,           --      --     500      --      --     --
Sodium Phosphate,        --      --      --     600      --     --
Sodium Bisulphite,       --      --      --     100      --     --


In the baths the gold is added in the form of neutral chloride, Auric
chloride (Au Cl6).

Gold Stripping Bath.
A bath for removing gold from plated articles without dissolving the
base in order to save the precious metal. A bath of 10 parts of
potassium cyanide and 100 parts of water may be used, the articles to be
stripped being immersed therein as the anode of an active circuit. If
the gilding is on a silver or copper basis, or on an alloy of these
metals the same solution attacks the base and dissolves it, which is
objectionable. For silver articles it is enough to heat to cherry red
and throw into dilute sulphuric acid. The gold scales off in metallic
spangles. For copper articles, a mixture of 10 volumes concentrated
sulphuric acid, 1 volume nitric acid, and 2 volumes hydrochloric acid
may be used by immersion only, or with a battery. The sulphuric acid in
such large excess is supposed to protect the copper. For copper articles
concentrated sulphuric acid alone with the battery may be used. This
does not sensibly attack the copper if it is not allowed to become
diluted. Even the dampness of the air may act to dilute it.

Apparatus for enabling the same line to be used for telegraph signals
and telephoning.

One type consists in coils with iron cores or simply electromagnets.
These act to retard the current in reaching its full power and also
prolong it. This gives a graduated effect to the signals, so that the
telephone diaphragm is not audibly affected by the impulses.

The telephoning current is so slight and so rapid in its characteristic
changes that it is without effect upon the ordinary telegraph.


The unit of weight in the metric system; accepted as the unit of
mass in the absolute of C. G. S. system of units. It is the
one-thousandth part of mass of a standard weight preserved under proper
conditions in Paris, and supposed to be the mass of a cubic decimeter of
distilled water at the temperature of the maximum density of water. The
standard is the kilogram; the temperature is 3.9º C. (39º F.). The
standard kilogram is found to be not exactly the weight of a cubic
decimeter of water, the latter weighing 1.000013 kilogram.

If therefore the defined gram on the water basis is taken as the unit it
varies very slightly from the accepted gram.

1 gram is equal to 15.43234874 grains. (Prof. W. H. Miller.)

The number of grams of an element equal numerically to the atomic
weight, as 16 grams of oxygen, 1 gram of hydrogen, 35.5 grams of
chlorine; all which might be expressed as gram-atoms of oxygen, hydrogen
and chlorine respectively.

The gram-atom approximately expresses the number of gram-calories
required to heat one gram of the substance 1º C. (1.8º F.). This is in
virtue of Dulong and Petit's discovery that the atomic weight of an
element multiplied by its specific heat gives approximately a constant
for all elements.

[Transcriber's note: A gram-atom is the mass, in grams, of one mole of
atoms in a monatomic element. A mole consists of Avogadro's number of
atoms, approximately 6.02214E23.]

The number of grams of a substance equal numerically to its molecular

Carbon; one of three allotropic modifications of this element. It occurs
in nature as a mineral.

It is used as a lubricant for machinery; for commutator brushes; for
making surfaces to be plated conductive, and for mixing with manganese
binoxide in Leclanché cells.

A natural force which causes all masses of matter to attract each other.
Its cause is unknown; it is often supposed to be due to the luminiferous

[Transcriber's note: Einstein's explanation of gravity, General
Relativity and the curvature of space-time, came 23 years later, 1915.]


Gravity, Acceleration of.
The velocity imparted to a body in one second by the action of
gravitation at any standard point upon the earth's surface in a vacuum.
This will vary at different places, owing principally to the variation
in centrifugal force due to the earth's rotation. For standard valuation
it must be reduced to sea level. The following are examples of its

Equator,          978.1028       centimeters per second
Paris,            980.94                   "
Greenwich         981.I7                   "
Edinburgh,        981.54                   "
Pole (N. or S.),  983.1084 (theoretical)   "

As round numbers for approximate calculations 981 centimeters or 32.2
feet may be employed.

[Transcriber's note: The acceleration of gravity at the equator is also
reduced by the increased distance from the center of the earth
(equatorial bulge). Increased altitude reduces gravity. Reduced air
density at altitude reduces buoyancy and increases apparent weight.
Local variations of rock density affects gravity.]

Gravity, Control.
Control by weight. In some ammeters and voltmeters gravity is the
controlling force.

A lead plate perforated or ridged for use in a storage battery as the
supporter of the active materials and in part as contributing thereto
from its own substance.

The contact of a conductor of an electric circuit with the earth,
permitting the escape of current if another ground exists.

A metaphorical term applied to the earth when used as a return circuit.


Grove's Gas Battery.
A voltaic battery depending for its action on the oxidation of hydrogen
instead of the oxidation of zinc. Its action is more particularly
described under Battery, Gas. In the cut B, B1 * * * are the terminals
of the positive or hydrogen electrodes, marked H, and A, Al * * * are
the terminals of the negative or oxygen electrodes marked O, while M, M1
* * * is dilute sulphuric acid.


Guard Ring.
An annular horizontal surface surrounding the balanced disc in the
absolute electrometer. (See Electrometer, Absolute.)

Guard Tube.
A metal tube surrounding a dry pile used with a quadrant electrometer,
or other electrometers of that type. It prevents the capacity of the
lower brass end of the pile (which brass end closes the glass tube
containing the discs) from momentary change by approach of some
conductor connected to the earth. There are other guard tubes also.

Gun, Electro-magnetic.
An electro-magnet with tubular core. If, when it is excited a piece of
an iron rod is pushed into the central aperture of the core and is
released, the magnetic circle will try to complete itself by pushing the
rod out so that it can thus be discharged, as if from a popgun.

Synonym--Electric Popgun.


Gutta Percha.
The hardened milky juice of a tree, the Isonandra gutta, growing in
Malacca and other parts of the Eastern Archipelago. It is much used as
an insulator or constituent of insulators.

Resistance after several minutes electrification per 1 centimeter cube
at 54º C. (75º F.),  4.50E14 ohms.

The specific resistance varies--from 2.5E13 to 5.0E14 ohms. A usual
specification is 2.0E14 ohms. The influence of temperature on its
resistance is given in Clark & Bright's empirical formula, R = R0 at, in
which R is the resistance at temperature tº C--Ro the resistance at 0º C
(32º F), a is the coefficient .8944.

The resistance increases with the time of passage of the current, the
variation being less the higher the temperature.


Time of            Relative Resistance     Relative Resistance
Electrification.   at 0º C (32º F.)        at 24º C (75º F.)
   1 minute        100                     5.51
   2   "           127.9                   6.
   5   "           163.1                   6.66
  10   "           190.9                   6.94
  20   "           230.8                   7.38
  30   "           250.6                   7.44
  60   "           290.4                   7.6
  90   "           318.3                   7.66

In cable testing one minute is generally taken as the time of

Pressure increases the resistance by the formula Rp=R (1+ .00327 P) in
which Rp is the resistance at pressure p--R resistance at atmospheric
pressure--p pressure in atmospheres. Thus in the ocean at a depth of
4,000 meters (2.4855 miles), the resistance is more than doubled. The
longer the pressure is applied, the greater is the resistance.

The specific inductive capacity of gutta percha is 4.2.

Good gutta percha should not break when struck with a hammer, should
recover its shape slowly, and it should support much more than 300 times
its own weight.

Gyrostatic Action of Armatures.
Owing to gyrostatic action a rotating armature resists any change of
direction of its axis. On ships and in railway motors which have to turn
curves this action occurs. A 148 lb. armature running at 1,300
revolutions per minute may press with 30 lbs. on each journal as the
ship rolls through an angle of 20° in 16 seconds.


(a) The symbol for the horizontal component of the earth's

(b) The symbol for the intensity of a magnetizing force or field. The
symbol H, as it is generally used, may mean either the number of dynes
which act upon a unit pole, or the number of lines of force per

(c) The symbol for the unit of self-induction.

Hair, Removal of, by Electrolysis.
A method of depilation by destruction of individual hair follicles by

A fine platinum electrode is thrust into a hair follicle. It is the
negative electrode. The positive electrode is in contact with the body
of the person under treatment; it is often a sponge electrode simply
held in his hand. A current of two to four milliamperes from an E. M. F.
of 15 to 20 volts, is passed. This destroys the follicle, the hair is
removed and never grows again. A gradual increase of current is advised
for the face. As only one hair is removed at once, but a small number
are taken out at a sitting.


Haldat's Figures.
With a pole of a strong bar magnet, used like a pencil, imaginary
figures are drawn upon a hard steel plate, such as a saw-blade. The
pattern is gone over several times. By dusting iron filings on a sheet
of paper laid over the steel plate, while horizontal, very complicated
magnetic figures are produced.

Hall's Experiment.
A cross of thin metal, such as gold leaf, is secured upon a pane of
glass. To two opposite arms a battery is connected in circuit with them.
To the other two arms a galvanometer is connected in circuit. If the
cross is put into a field of force whose lines are perpendicular
thereto, the galvanometer will disclose a constant current. The current
is pushed, as it were, into the galvanometer circuit. Other metals have
been used with similar results. They must be thin or the experiment
fails. If the arm receiving the battery current is horizontal, and if it
flows from left to right, and if the lines of force go from downward
through the cross, the current in the galvanometer circuit will flow
from the observer through the other arms of the cross, if the cross is
of gold, silver, platinum or tin, and the reverse if of iron. The
experiment has indicated a possible way of reaching the velocity of
electricity in absolute measure.

Hall Effect.
The effect observed in Hall's experiment, q. v.

Hall Effect, Real.
A transverse electro-motive force in a conductor through which a current
is passing produced by a magnetic field.

Hall Effect, Spurious.
A spurious electro-motive force produced in a conductor, through which a
current is passing by changes in conductivity of the conductor brought
about by a magnetic field.

Hanger Board.
A board containing two terminals, a suspending hook, and a switch, so
that an arc lamp can be introduced into a circuit thereby, or can be
removed as desired.

Harmonic Receiver.
A receiver containing a vibrating reed, acted on by an electro-magnet.
Such a reed answers only to impulses tuned to its own pitch. If such are
received from the magnet it will vibrate. Impulses not in tune with it
will not affect it. (See Telegraph, Harmonic.)

Head Bath, Electric.
A fanciful name for an electro-medical treatment of the head. The
patient is insulated by an insulating stool or otherwise. His person is
connected with one terminal of an influence machine. An insulated
metallic circle, with points of metal projecting inward or downward, is
placed about the head. The circle is connected with the other pole of
the machine. On working it a silent or brush discharge with air
convection streams occurs between the patient's head and the circle of


Head-light, Electric.
An electric head-light for locomotives has been experimented with. It
includes the parabolic reflection of the regular light with an arc-lamp
in place of the oil lamp. An incandescent lamp may be used in the same
place, but has no great advantage over oil as regards illuminating

A form of kinetic energy, due to a confused oscillatory movement of the
molecules of a body. Heat is not motion, as a heated body does not
change its place; it is not momentum, but it is the energy of motion. If
the quantity of molecular motion is doubled the momentum of the
molecules is also doubled, but the molecular mechanical energy or heat
is quadrupled.

As a form of energy it is measured by thermal units. The calorie is the
most important, and unfortunately the same term applies to two units,
the gram-degree C. and the kilogram-degree C. (See Calorie.) Calories
are determined by a calorimeter, q. v.

Independent of quantity of heat a body may be hotter or colder.
Thermometers are used to determine its temperature.

Heat is transmitted by conduction, a body conducting it slowly for some
distance through its own substance. Bodies vary greatly in their
conductivity for heat. It is also transmitted by convection of gases or
liquids, when the heated molecules traveling through the mass impart
their heat to other parts. Finally it is transmitted by ether waves with
probably the speed of light. This mode of transmission and the phenomena
of it were attributed to radiant heat. As a scientific term this is now
dropped by many scientists. This practice very properly restricts the
term "heat" to kinetic molecular motion.

The mechanical equivalent of heat is the number of units of work which
the energy of one unit quantity of heat represents. (See Equivalents,
Mechanical and Physical.)

Heat, Atomic.
The product of the specific heat of an element by its atomic weight. The
product is approximately the same for all the elements, and varies as
determined between 5.39 and 6.87. The variations are by some attributed
principally to imperfection of the work in determining them. The atomic
heat represents the number of gram calories required to raise the
temperature of a gram atom (a number of grams equal numerically to the
atomic weight) one degree centigrade.


Heat, Electric.
This term has been given to the heat produced by the passage of a
current of electricity through a conductor. It is really electrically
produced heat, the above term being a misnomer.

The rise of temperature produced in a cylindrical conductor by a current
depends upon the diameter of the conductor and on the current. The
length of the wire has only the indirect connection that the current
will depend upon the resistance and consequently upon its length.

The quantity of heat produced in a conductor by a current is in
gram-degree C. units equal to the product of the current, by the
electro-motive force or potential difference maintained between the ends
of the wire, by .24.

The cube of the diameter of a wire for a given rise of temperature
produced in such conductor by a current is equal approximately to the
product of the square of the current, by the specific resistance (q. v.)
of the material of the conductor, by .000391, the whole divided by the
desired temperature in centigrade units.

Heat, Electrical Convection of.
A term applied to the phenomena included under the Thomson effect, q.
v., the unequal or differential heating effect produced by a current of
electricity in conductors whose different parts are maintained at
different temperatures.

Heater, Electric.
An apparatus for converting electrical energy into thermal energy.

An incandescent lamp represents the principle, and in the Edison meter
has been used as such to maintain the temperature of the solutions.
Heaters for warming water and other purposes have been constructed,
utilizing conductors heated by the passage of the current as a source of
heat. (See also Heating Magnet.)

Heating Error.
In voltmeters the error due to alteration of resistance of the coil by
heating. If too strong a current is sent through the instrument, the
coils become heated and their resistance increased. They then do not
pass as much current as they should for the potential difference to
which they may be exposed. Their readings then will be too low. One way
of avoiding the trouble is to have a key in circuit, and to pass only an
instantaneous or very brief current through the instrument and thus get
the reading before the coils have time to heat.

The heating error does not exist for ammeters, as they are constructed
to receive the entire current, and any heating "error" within their
range is allowed for in the dividing of the scale.

Heating Magnet.
An electro-magnet designed to be heated by Foucault currents induced in
its core by varying currents in the windings. It has been proposed as a
source of artificial heat, a species of electric heating apparatus for
warming water, or other purposes.


Heat, Irreversible.
The heat produced by an electric current in a conductor of identical
qualities and temperature throughout. Such heat is the same whatever the
direction of the current. The heating effect is irreversible because of
the absence of the Thomson effect, q. v.) or Peltier effect, q. v.

Heat, Mechanical Equivalent of.
The mechanical energy corresponding to a given quantity of heat energy.
Mechanical energy is generally represented by some unit of weight and
height, such as the foot-pound; and heat energy is represented by a
given weight of water heated a given amount, such as a pound-degree
centigrade. Joule's equivalent is usually accepted; it states that
772.55 foot pounds of mechanical energy are equivalent to 1 pound-degree
F. (one pound avds. of water raised in temperature one degree
Fahrenheit). Other equivalencies have also been deduced.

Heat, Molecular.
The product of a specific heat of the compound by its molecular weight.
It is approximately equal to the sum of the atomic heats of its
constituent elements.

The molecular heat represents the number of gram calories required to
raise the temperature of a gram-molecule (a number of grams equal
numerically to the molecular weight) one degree centigrade.

The molecular heat is approximately equal for all substances.

Heat, Specific.
The capacity of a body for heat; a coefficient representing the relative
quantity of heat required to raise the temperature of an identical
weight of a given body a defined and identical amount.

The standard of comparison is water; its specific heat is taken as
unity. The specific heats by weight of other substances are less than
unity. The specific heat varies with the temperature. Thus the specific
heat of water is more strictly 1+.00015 tº C.

Specific heat is greater when a substance is in the liquid than when it
is in the solid state. Thus the specific heat of ice is 0.489; less
than half that of water. It differs with the allotropic modifications of
bodies; the specific heat of graphite is .202; of diamond, .147.

The product of the specific heat by the atomic weight of elements gives
a figure approximately the same. A similar law applies in the case of
molecules. (See Heat, Atomic-Heat, Molecular.)

The true specific heat of a substance should be separated from the heat
expended in expanding a body against molecular and atomic forces, and
against the atmospheric pressure. So far this separation has not been
possible to introduce in any calculations.


Heat, Specific, of Electricity.
A proposed term to account for the heat absorbed or given out in
unhomogeneous conductors, by the Thomson effect, or Peltier effect (see
Effect, Thomson--Effect, Peltier.) If a current of electricity be
assumed to exist, then under the action of these effects it may be
regarded as absorbing or giving out so many coulombs of heat, and thus
establishing a basis for specific heat.

Heat Units.
The British unit of heat is the pound degree F--the quantity of heat
required to raise the temperature of a pound of water from 32° to 33° F.

The C. G. S. unit is the gram-degree C.; another metric unit is the
kilogram-degree C. The latter is the calorie; the former is sometimes
called the small calorie or the joule; the latter is sometimes called
the large calorie. The term joule is also applied to a quantity of heat
equivalent to the energy of a watt-second or volt-coulomb. This is equal
to .24l gram degree calorie.

A prefix to terms of measurement--meaning one hundred times, as
hectometer, one hundred meters.

An apparatus for reflecting flashes of light to a distant observer. By
using the Morse telegraph code messages may thus be transmitted long
distances. When possible the sun's light is used.

A coil of wire; properly a coil wound so as to follow the outlines of a
screw without overlaying itself.



The practical unit of electro-magnetic or magnetic inductance. It is
equal to 1E9 C. G. S., or absolute units of inductance. As the
dimensions of inductance are a length the henry is equal to 1E9
centimeters, or approximately to one quadrant of the earth measured on
the meridian.



Hermetically Sealed.
Closed absolutely tight. Glass vessels, such as the bulbs of
incandescent lamps, are hermetically sealed often by melting the glass
together over any opening into their interior.

Heterostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer Absolute.) The formula for its idiostatic use, q. v.,
involves the determination of d, the distance between the suspended and
fixed discs. As this is difficult to determine the suspended disc and
guard ring may be kept at one potential and the lower fixed disc is then
connected successively with the two points whose potential difference is
to be determined. Their difference is determined by the difference
between d and d', the two distances between the discs. This difference
is the distance through which the micrometer screw is moved. The
heterostatic formula is:

V' - V = (d' - d)* squareRoot( 8*PI*F / S )

in which V and V' are potentials of the two points; d' and d the two
distances between the discs necessary for equilibrium; S the area of the
disc and F the force of attraction in dynes. (See Idiostatic Method.)

High Bars of Commutator.
Commutator bars, which in the natural wear of the commutator, project
beyond the others. The surface then requires turning down, as it should
be quite cylindrical.

High Frequency.
A term used as a noun or as an adjective to indicate in an alternating
current, the production of a very great number of alternations per unit
of time--usually expressed as alternations per second.

A term applied to a noise sometimes produced by a voltaic arc; probably
due to the same cause as frying, q. v.

Hittorf's Solution.
A solution used as a resistance. It is a solution of cadmium iodide in
amylic alcohol. Ten per cent. of the salt is used. It is contained in a
tube with metallic cadmium electrodes. (See Resistance, Hittorf' s.)



(a) The adjustable clamps for holding the armature brushes of dynamos
and motors.

(b) The clamps for holding the carbons of arc lamps.

(c) The clamps for holding safety fuses, q. v.

(d) Holders for Jablochkoff candles and other electric candles. (See
Candle Holders.)

(e) A box or block of porcelain for holding safety fuses.

A tin hood placed over an arc-lamp. Such hoods are often truncated cones
in shape, with the small end upwards. They reflect a certain amount of
light besides protecting the lamp to some extent from rain.

The extensions of the pole pieces of a dynamo or motor. (See Following
Horns-Leading Horns.)

Synonym--Pole Tips.

Horse Power.
A unit of rate of work or activity. There are two horse powers.

The British horse power is equal to 33,000 pounds raised one foot per
minute, or 550 foot pounds per second, or 1.0138 metric horse power.

The metric horse power (French) is equal to 75 kilogram-meters, or 542
foot pounds per second, or .986356 British horse power.

H. P. is the abbreviation for horse power. (See Horse Power, Electric.)

Horse Power, Actual.
The rate of activity of a machine, as actually developed in condition
for use. It is less than the indicated or total horse power, because
diminished by the hurtful resistances of friction, and other sources of
waste. It is the horse power that can be used in practise, and which in
the case of a motor can be taken from the fly-wheel.

Horse Power, Electric.
The equivalent of a mechanical horse power in electric units, generally
in volt-amperes or watts; 745.943 watts are equivalent to the activity
of one British horse power; 735.75 are equivalent to one metric horse
power. The number 746 is usually taken in practical calculations to give
the equivalency.

[Transcriber's note: Contemporary values are: Mechanical (British)
horsepower = 745.6999 Watts; Metric horsepower = 735.49875 Watts]

Horse Power, Indicated.
The horse power of an engine as indicated by its steam pressure, length
of stroke, and piston area, and vacuum, without making any deduction for
friction or hurtful resistances. The steam pressure is in accurate work
deduced from indicator diagrams.

Horse Power, Hour.
A horse power exerted for one hour, or the equivalent thereof. As the
horse power is a unit of activity, the horse power hour is a unit of
work or of energy. It is equal to 1,980,000 foot pounds.

H. P.
Abbreviation for "horse power."


Hughes' Electro-magnet.
A horseshoe electro-magnet with polarized core. It is made by mounting
two bobbins of insulated wire on the ends of a permanent horseshoe
magnet. It was devised for use in Hughes' printing telegraph, where very
quick action is required. The contact lasts only .053 second, 185
letters being transmitted per minute.



Hughes' Induction Balance.
An apparatus for determining the presence of a concealed mass of metal.
The apparatus is variously connected. The cut shows a representative
form; a and a' are two primary coils, each consisting of 100 meters (328
feet) of No. 32 silk covered copper wire (0.009 inch diameter) wound on
a boxwood spool ten inches in depth; b and b' are secondary coils. All
coils are supposed to be alike. The primary coils are joined in series
with a battery of three or four Daniell cells. A microphone m is
included in the same circuit. The secondary coils are joined in series
with a telephone and in opposition with each other. The clock is used to
produce a sound affecting the microphone. If all is exactly balanced
there will be no sound produced in the telephone. This balance is
brought about by slightly varying the distance of one of the secondaries
from the primary, until there is no sound in the telephone. If now a
piece of metal is placed within either of the coils, it disturbs the
balance and the telephone sounds.


To measure the forces acting a sonometer or audiometer is used. This is
shown in the upper part of the cut. Two fixed coils, c and e are mounted
at the ends of a graduated bar. A movable coil d is connected in the
telephone circuit; c and e by a switch can be connected with the battery
and microphone circuit, leaving out the induction balance coils. The
ends of the coils c and e, facing each other are of the same polarity.
If these coils, c and e, were equal in all respects, no sound would be
produced when d was midway between them. But they are so wound that the
zero position for d is very near one of them, c.

Assume that a balance has been obtained in the induction balance with
the coil d at zero. No sound is heard whether the switch is moved to
throw the current into one or the other circuit. A piece of metal placed
in one of the balance coils will cause the production of a sound. The
current is turned into the sonometer and d is moved until the same
sound, as tested by rapid movements of the switch, is heard in both
circuits. The displacement of d gives the value of the sound.

A milligram of copper is enough to produce a loud sound. Two coins can
be balanced against each other, and by rubbing one of them, or by
breathing on one of them, the balance will be disturbed and a sound will
be produced.

Prof. Hughes has also dispensed with the audiometer. He has used a strip
of zinc tapering from a width of 4 mm. (.16 inch) at one end to a sharp
edge or point at the other. The piece to be tested being in place in one
coil, the strip is moved across the face of the other until a balance is

As possible uses the detection of counterfeit coins, the testing of
metals for similarity of composition and the location of bullets in the
body have been suggested. Care has to be taken that no masses of metal
interfere. Thus in tests of the person of a wounded man, the presence of
an iron truss, or of metallic bed springs may invalidate all

The same principle is carried out in an apparatus in which the parts are
arranged like the members of a Wheatstone bridge. One pair of coils is
used, which react on each other as primary and secondary coils. One of
the coils is in series with a telephone in the member of the bridge
corresponding to that containing the galvanometer of the Wheatstone
bridge. The latter is more properly termed an induction bridge.

Synonyms--Inductance Bridge--Inductance Balance--Induction Bridge.


Hydro-electric. adj.
(a) A current produced by a voltaic couple or the couple itself is
sometimes thus characterized or designated as a "hydro-electric current"
or a "hydro-electric couple." It distinguishes them from

(b) Armstrong's steam boiler electric machine (see Hydroelectric
Machine) is also termed a hydro-electric machine.

Hydro-electric Machine.
An apparatus for generating high potential difference by the escape of
steam through proper nozzles.

It consists of a boiler mounted on four glass legs or otherwise
insulated. An escape pipe terminates in a series of outlets so shaped as
to impede the escape of the steam by forcing it out of the direct
course. These jets are lined with hard wood. They are enclosed in or led
through a box which is filled with cold water.


This is to partly condense the steam so as to get it into the vesicular
state, which is found essential to its action. Dry steam produces no
excitation. If the boiler is fired and the steam is permitted to escape
under the above conditions the vesicles presumably, or the "steam" is
found to be electrified. A collecting comb held against the jet becomes
charged and charges any connected surface.


The boiler in the above case is negatively and the escaping "steam" is
positively charged. By changing the material of the linings of the jets,
or by adding turpentine the sign of the electricity is reversed. If the
water contains acid or salts no electricity is produced. The regular
hydro-electric machine is due to Sir William Armstrong.

Faraday obtained similar results with moist air currents.

An element existing under all except the most extreme artificial
conditions of pressure and cold as a gas. It is the lightest of known
substances. Atomic weight, 1; molecular weight, 2; equivalent, 1;
valency, 1; specific gravity, .0691-.0695. (Dumas & Boussingault.)

It is a dielectric of about the same resistance as air. Its specific
inductive capacity at atmospheric pressure is:
    .9997 (Baltzman)   .9998 (Ayrton)

Electro-chemical equivalent, .0105 milligram.
The above is usually taken as correct. Other values are as follows:
.010521 (Kohllrausch)   .010415 (Mascart)

The electro-chemical equivalent of any element is obtained by
multiplying its equivalent by the electro-chemical equivalent of
hydrogen. The value .0105 has been used throughout this book.

An instrument for determining the moisture in the air. One form consists
of a pair of thermometers, one of which has its bulb wrapped in cloth
which is kept moist during the observation. The evaporation is more or
less rapid according to the dryness or moisture of the air, and as the
temperature varies with this evaporation the relative readings of the
two thermometers give the basis for calculating the hygrometric state of
the air. Another form determines the temperature at which dew is
deposited on a silver surface, whence the calculations are made.

Hysteresis, Magnetic.
A phenomenon of magnetization of iron. It may be attributed to a sort of
internal or molecular friction, causing energy to be absorbed when iron
is magnetized. Whenever therefore the polarity or direction of
magnetization of a mass of iron is rapidly changed a considerable
expenditure of energy is required. It is attributed to the work done in
bringing the molecules into the position of polarity.


The electric energy lost by hysteresis may be reduced by vibrations or
jarring imparted to the iron, thus virtually substituting mechanical for
electrical work.

On account of hysteresis the induced magnetization of a piece of iron or
steel for fields of low intensity will depend on the manner in which the
material has been already magnetized. Let the intensity of field
increase, the magnetization increasing also; then lower the intensity;
the substance tends to and does retain some of its magnetism. Then on
again strengthening the field it will have something to build on, so
that when it attains its former intensity the magnetization will exceed
its former value. For a moderate value of intensity of field the
magnetization can have many values within certain limits.

Synonym--Hysteresis--Hysteresis, Static--Magnetic Friction.

Hysteresis, Viscous.
The gradual increase or creeping up of magnetization when a magnetic
force is applied with absolute steadiness to a piece of iron. It may
last for half an hour or more and amount to several per cent. of the
total magnetization. It is a true magnetic lag.


A symbol sometimes used to indicate current intensity. Thus Ohm's law is
often expressed I = E/R, meaning current intensity is equal to
electro-motive force divided by resistance. C is the more general symbol
for current intensity.

Ideoelectrics or Idioelectrics.
Bodies which become electric by friction. This was the old definition,
the term originating with Gilbert. It was based on a misconception, as
insulation is all that is requisite for frictional electrification,
metals being thus electrified if held by insulating handles. The term is
virtually obsolete; as far as it means anything it means insulating
substances such as scaling wax, sulphur, or glass.

Idle Coils.
Coils in a dynamo, in which coils no electro-motive force is being
generated. This may occur when, as a coil breaks connection with the
commutator brush, it enters a region void of lines of magnetic force, or
where the lines are tangential to the circle of the armature.

Idiostatic Method.
A method of using the absolute or attracted disc electrometer. (See
Electrometer, Absolute.) The suspended disc and guard ring are kept at
the same potential, which is that of one of the points whose potential
difference is to be determined; the lower fixed disc is connected to the
other of the points whose potential difference is to be determined. Then
we have the formula

V = d * SquareRoot( 8 * PI * F ) / S

in which d is the distance between the discs, V is the difference of
potential of the two points, F the force of attraction between the discs
in dynes, and S the area of the suspended disc. (See Heterostatic


Idle Poles.
Poles of wire sealed into Crookes' tubes, not used for the discharge
connections, but for experimental connections to test the effect of
different excitation on the discharge.

Idle Wire.
In a dynamo the wire which plays no part in generating electro-motive
force. In a Gramme ring the wire on the inside of the ring is idle wire.

In arc lamps with fixed parallel carbons of the Jablochkoff type (see
Candle, Jablochkoff) a strip of carbon connects the ends of the carbons
in the unused candle. This is necessary to start the current. Such strip
is called an igniter. It burns away in a very short time when an arc
forms producing the light, and lasts, if all goes well, until the candle
burns down to its end. Without the igniter the current would not start
and no arc would form.

I. H. P.
Symbol for indicated horse-power.

Illuminating Power.
The relative light given by any source compared with a standard light,
and stated in terms of the same, as a burner giving an illuminating
power of sixteen candles. For standards see Candle, Carcel--Methven
Standard--Pentane Standard.

Illuminating Power, Spherical.
The illuminating power of a lamp or source of light may vary in
different directions, as in the case of a gas burner or incandescent
lamp. The average illuminating power determined by photometric test or
by calculation in all directions from the source of light is called the
spherical illuminating power, or if stated in candles is called the
spherical candle power.

Illumination, Unit of.
An absolute standard of light received by a surface. Preece proposed as
such the light received from a standard candle (see Candle, Standard) at
a distance of 12.7 inches. The object of selecting this distance was to
make it equal to the Carcel Standard (see Carcel), which is the light
given by a Carcel lamp at a distance of one meter.

From one-tenth to one-fiftieth this degree of illumination was found in
gas-lighted streets by Preece, depending on the proximity of the gas

Image, Electric.
An electrified point or system of points on one side of a surface which
would produce on the other side of that surface the same electrical
action which the actual electrification of that surface really does
produce. (Maxwell.)

The method of investigating the distribution of electricity by electric
images is due to Sir William Thomson. The conception is purely a
theoretical one, and is of mathematical value and interest.


The ratio of any impressed electro-motive force to the current which it
produces in a conductor. For steady currents it is only the resistance.
For variable currents it may include besides resistance inductance and
permittance. It is the sum of all factors opposing a current, both ohmic
and spurious resistances. It is often determined and expressed as ohms.

Synonym--Apparent Resistance--Virtual Resistance.

Impedance, Oscillatory.
The counter-electro-motive force offered to an oscillatory discharge, as
that of a Leyden jar. It varies with the frequency of the discharge

Synonym--Impulsive Impedance.

Impressed Electro-motive Force.
The electro-motive force expending itself in producing current induction
in a neighboring circuit.

(a) An electro-magnetic impulse is the impulse produced upon the
luminiferous ether by an oscillatory discharge or other varying type of
current; the impulse is supposed to be identical, except as regards
wave-length, with a light wave.

(b) An electro-motive impulse is the electro-motive force which rises so
high as to produce an impulsive or oscillatory discharge, such as that
of a Leyden jar.

Incandescence, Electric.
The heating or a conductor to red, or, more etymologically, to white
heat by the passage of an electric current. The practical conditions are
a high intensity of current and a low degree of conductance of the
conductor relatively speaking.

Inclination Map.
A map showing the locus of equal inclination or dips of the magnetic
needle. The map shows a series of lines, each one of which follows the
places at which the dip of the magnetic needle is identical. The map
changes from year to year. (See Magnetic Elements.)

Independence of Currents in Parallel Circuits.
If a number of parallel circuits of comparatively high resistance are
supplied by a single generator of comparatively low resistance, the
current passed through each one will be almost the same whether a single
one or all are connected. Under the conditions named the currents are
practically independent of each other.

[Transcriber's note: The current in each parallel branch depends on the
resistance/impedance of that branch. Only if they all have the same
impedance will the current be the same.]

Indicating Bell.
An electric bell arranged to drop a shutter or disclose in some other
way a designating number or character when rung.


(a) An apparatus for indicating the condition of a distant element, such
as the water level in a reservoir, the temperature of a drying room or
cold storage room or any other datum. They are of the most varied

(b) The receiving instrument in a telegraph system is sometimes thus

Indicator, Circuit.
A galvanometer used to show when a circuit is active, and to give an
approximate measurement of its strength. It is a less accurate and
delicate form of instrument than the laboratory appliance.

The property of a circuit in virtue of which it exercises induction and
develops lines of force. It is defined variously. As clear and
satisfactory a definition as any is the following, due to Sumpner and
Fleming: Inductance is the ratio between the total induction through a
circuit to the current producing it. "Thus taking a simple helix of five
turns carrying a current of two units, and assuming that 1,000 lines of
force passed through the central turn, of which owing to leakage only
900 thread the next adjacent on each side, and again only 800 through
the end turns, there would be 800 + 900 + 1000 + 900 + 800, or 4,400
linkages of lines with the wire, and this being with 2 units of current,
there would be 2,200 linkages with unit current, and consequently the
self-inductance of the helix would be 2,200 centimetres." (Kennelly.)
Inductance, as regards its dimensions is usually reduced to a length,
hence the last word of the preceding quotation.

The practical unit of inductance is termed the henry, from Prof. Joseph
Henry; the secohm, or the quad or quadrant. The latter alludes to the
quadrant of the earth, the value in length of the unit in question.

[Transcriber's note: (L (di/dt) = V). A current changing at the rate of
one ampere per second through a one henry inductance produces one volt.
A sinusoidal current produces a voltage 90 degrees ahead of the current,
a cosine (the derivative of sine is cosine). One volt across one henry
causes the current to increase at one ampere per second.]

Induction, Coefficient of Self.
The coefficient of self-induction of a circuit is the quantity of
induction passing through it per unit current in it. If a given circuit
is carrying a varying current it is producing a varying quantity of
magnetic induction through itself. The quantity of induction through the
circuit due to its current is generally proportional to its current. The
quantity for unit current is the coefficient of self-induction.

Induction, Cross.
The induction of magnetic lines of force in a dynamo armature core by
the current passing around such armature. These lines in a symmetrical
two pole machine are at right angles to the lines of force which would
normally extend across the space between the two magnet poles. The joint
magnetizing effect of the field and of the cross induction produces a
distorted field between the poles .

Synonym--Cross-magnetizing Effect.


Induction, Electro-magnetic.
The inter-reaction of electromagnetic lines of force with the production
of currents thereby.

A current passing through a conductor establishes around it a field of
force representing a series of circular lines of force concentric with
the axis of the conductor and perpendicular thereto. These lines of
force have attributed to them, as a representative of their polarity,
direction. This is of course purely conventional. If one is supposed to
be looking at the end of a section of conductor, assuming a current be
passing through it towards the observer, the lines of force will have a
direction opposite to the motion of the hands of a watch. The idea of
direction may be referred to a magnet. In it the lines of force are
assumed to go from the north pole through the air or other surrounding
dielectric to the south pole.

Two parallel wires having currents passing through them in the same
direction will attract each other. This is because the oppositely
directed segments of lines of force between the conductors destroy each
other, and the resultant of the two circles is an approximation to an
ellipse. As lines of force tend to be as short as possible the
conductors tend to approach each other to make the ellipse become of as
small area as possible, in other words to become a circle.

If on the other hand the currents in the conductors are in opposite
directions the segments of the lines of force between them will have
similar directions, will, as it were, crowd the intervening ether and
the wires will be repelled.


By Ampére's theory of magnetism, (see Magnetism, Ampére's Theory of,) a
magnet is assumed to be encircled by currents moving in the direction
opposite to that of the hands of a watch as the observer faces the north
pole. A magnet near a wire tends to place the Ampérian currents parallel
to the wire, and so that the portion of the Ampérian currents nearest
thereto will correspond in direction with the current in the wire.


This is the principle of the galvanometer. A number of methods of
memoria technica have been proposed to remember it by.

Thus if we imagine a person swimming with the current and always facing
the axis of the conductor, a magnetic needle held where the person is
supposed to be will have its north pole deflected to the right hand of
the person.


Again if we think of a corkscrew, which as it is turned screws itself
along with the current, the motion of the handle shows the direction of
the lines of force and the direction in which the north pole of a needle
is deflected. This much is perhaps more properly electro-dynamics, but
is necessary as a basis for the expression of induction.

If a current is varied in intensity in one conductor it will induce a
temporary current in another conductor, part of which is parallel to the
inducing current and which conductor is closed so as to form a circuit.
If the inducing current is decreased the induced current in the near and
parallel portion of the other circuit will be of identical direction; if
increased the induced current will be of opposite direction.

This is easiest figured by thinking of the lines of force surrounding
the inducing conductor. If the current is decreased these can be
imagined as receiving a twist or turn contrary to their normal
direction, as thereby establishing a turn or twist in the ether
surrounding the other wire corresponding in direction with the direction
of the original lines of force, or what is the same thing, opposite in
direction to the original twist. But we may assume that the
establishment of such a disturbance causes a current, which must be
governed in direction with the requirements of the new lines of force.

The same reasoning applies to the opposite case.


The general statement of a variable current acting on a neighboring
circuit also applies to the approach or recession of an unvarying
current, and to the cutting of lines of force by a conductor at right
angles thereto. For it is evident that the case of a varying current is
the case of a varying number of lines of force cutting or being cut by
the neighboring conductor. As lines of force always imply a current,
they always imply a direction of such current. The cutting of any lines
of force by a closed conductor always implies a change of position with
reference to all portions of such conductor and to the current and
consequently an induced current or currents in one or the other
direction in the moving conductor.

As the inducing of a current represents energy abstracted from that of
the inducing circuit, the direction of the induced current is determined
by (Lenz's Law) the rule that the new current will increase already
existing resistances or develop new ones to the disturbance of the
inducing field.

In saying that a conductor cutting lines of force at right angles to
itself has a current induced in it, it must be understood that if not at
right angles the right angle component of the direction of the wire acts
in generating the current. The case resolves itself into the number of
lines of force cut at any angle by the moving wire.

The lines of force may be produced by a magnet, permanent or electro.
This introduces no new element. The magnet may be referred, as regards
direction of its lines of force, to its encircling currents, actual or
Ampérian, and the application of the laws just cited will cover all

Induction, Coefficient of Mutual.
The coefficient of mutual induction of two circuits is the quantity of
magnetic induction passing through either of them per unit current in
the other. (Emtage.) It is also defined as the work which must be done
on either circuit, against the action of unit current in each, to take
it away from its given position to an infinite distance from the other;
and also as the work which would be done by either circuit on the other
in consequence of unit current in each, as the other moves from an
infinite distance to its given position with respect to the other
conductor. It depends on the form, size, and relative position of the
two circuits; and on the magnetic susceptibilities of neighboring

The ether surrounding two circuits of intensity i' and i" must possess
energy, expressible (Maxwell) as 1/2 L i2 + M i i + 1/2 N i12. It can be
shown that M i i1 in any given position of the two circuits is
numerically equal (1) to the mutual potential energy of the two circuits
(2) to the number of lines of induction, which being due to A, pass from
A through B, or equally being due to B, pass from B through A, and M is
styled the coefficient of mutual induction. (Daniell.)


Induction, Electrostatic.
An electrostatic charge has always an opposite and bound charge. This
may be so distributed as not to be distinguishable, in which case the
charge is termed, incorrectly but conventionally, a free charge. But
when a charge is produced an opposite and equal one always is formed,
which is the bound charge. The region between the two charges and
permeated by their lines of force, often curving out so as to embrace a
volume of cross-sectional area larger than the mean facing area of the
excited surfaces, is an electrostatic field of force. The establishing
of an electrostatic field, and the production of a bound charge are
electrostatic induction.

An insulated conductor brought into such a field suffers a
redistribution of its electricity, or undergoes electrostatic induction.
The parts nearest respectively, the two loci of the original and the
bound charges, are excited oppositely to such charges. The conductor
presents two new bound charges, one referred to the original charge, the
other to the first bound charge.

Induction, Horizontal.
In an iron or steel ship the induction exercised upon the compass needle
by the horizontal members of the structure, such as deck-beams, when
they are polarized by the earth's magnetic induction. This induction
disappears four times in swinging a ship through a circle; deviation due
to it is termed quadrantal deviation. (See Deviation, Quadrantal.)

Induction, Lateral.
A term formerly used to express the phenomenon of the alternative
discharge of a Leyden jar or other oscillatory discharge of electricity.
(See Discharge, Alternative.)

Induction, Magnetic.
The magnetization of iron or other paramagnetic substance by a magnetic

On account of its permeability or multiplying power for lines of force,
a paramagnetic body always concentrates lines of force in itself if
placed in a magnetic field, and hence becomes for the time being a
magnet, or is said to be polarized.

As the tendency of lines of force is to follow the most permeable path,
a paramagnetic bar places itself lengthwise or parallel with the
prevailing direction of the lines of force so as to carry them as far on
their way as possible. Every other position of the bar is one of
unstable equilibrium or of no equilibrium. The end of the bar where the
lines of force enter (see Lines of Force) is a south pole and is
attracted towards the north pole of the magnet.

The production of magnetic poles under these conditions in the bar is
shown by throwing iron filings upon it. They adhere to both ends but not
to the middle.

Induction, Mutual, Electro-magnetic.
The induction due to two electric currents reacting on each other.


Induction, Mutual, Electrostatic.
A charged body always induces a charge upon any other body near it; and
the same charge in the second body will induce the other charge in the
first body if the latter is unexcited. In other words the second body's
induction from the first is the measure of the charge the second would
require to induce in the first its own (the second's) induced charge.
This is the law of mutual electrostatic induction.

Induction, Open Circuit.
Inductive effects produced in open circuits. By oscillatory discharges a
discharge can be produced across a break in a circuit otherwise
complete. The requirements for its production involve a correspondence
or relation of its dimensions to the inducing discharge. The whole is
analogous to the phenomena of sound resonators and sympathetic
vibrations. Synonym--Oscillatory induction.

Induction, Self-.
(a) A phenomenon of electric currents analogous to the inertia of
matter. Just as water which fills a pipe would resist a sudden change in
its rate of motion, whether to start from rest, to cease or decrease its
motion, so an electric current requires an appreciable time to start and
stop. It is produced most strongly in a coiled conductor, especially if
a core of iron is contained within it.

As in the case of two parallel wires, one bearing currents which vary,
momentary currents are induced in the other wire, so in a single
conductor a species of inertia is found which retards and prolongs the
current. If a single conductor is twisted into a helix or corresponding
shape, its separate turns react one on the other in accordance with the
general principles of electromagnetic induction. (See Induction,
Electro-magnetic.) Thus when a current is suddenly formed the coils
acting upon each other retard for an instant its passage, producing the
effect of a reverse induced current or extra current opposing the
principal current. Of course no extra current is perceptible, but only
the diminution. When the current is passing regularly and the current is
broken, the corresponding action prolongs the current or rather
intensifies it for an instant, producing the true extra current. This is
current self-induction.

[Transcriber's note: See inductance.]

Synonyms--Electric Inertia--Electro-dynamic Capacity.

(b) A permanent magnet is said to tend to repel its own magnetism, and
thus to weaken itself; the tendency is due to magnetic self-induction.

Induction Sheath.
In the brush dynamo a thin sheet of copper surrounding the magnet cores
with edges soldered together. The winding is outside of it. Its object
is to absorb extra currents set up by variations in magnetic intensity
in the cores. These currents otherwise would circulate in the cores.


Induction, Unit of Self-.
The unit of self-induction is the same as that of induction in general.
It is the henry, q. v.

Induction, Unipolar.
Induction produced in a conductor which continuously cuts the lines of
force issuing from one pole of a magnet. As the lines of force are
always cut in the same sense a continuous and constant direction current
is produced.

Induction, Vertical.
In an iron or steel ship the induction or attraction exercised in the
compass by vertical elements of the structure. Such vertical masses of
iron in the northern hemisphere would have their upper ends polarized as
south poles, and would affect the magnet as soon as the vessel swung out
of the magnetic meridian. Thus this induction disappears twice in
swinging a ship through a complete circle; deviation due to it is termed
semi-circular deviation. (See Deviation, Semi-circular.)


A method of train telegraphy. The train carries a circuit including a
coil, and messages are picked up by it from coils along the line into
which an alternating current is passed. A telephone is used as a
receiver in place of a sounder or relay. The invention, never
practically used, is due to Willoughby Smith.


(a) In a current generator a mass of iron, generally laminated, which is
moved past a magnet pole to increase the number of lines of force
issuing therefrom. It is used in inductor dynamos. (See Dynamo
Inductor.) In the cut Fig. 202, of an inductor dynamo i, i, are the
laminated inductors.

(b) In influence machines the paper or tinfoil armatures on which the
electrification is induced.

A force in virtue of which every body persists in its state of motion or
rest except so far as it is acted on by some force.

Inertia, Electro-magnetic.
This term is sometimes applied to the phenomena of self-induction, or
rather to the cause of these phenomena.

Infinity Plug.
A plug in a resistance box, which on being pulled out of its seat opens
the circuit or makes it of infinite resistance. The plug seats itself
between two brass plates which are not connected with each other in any
way. The other plates are connected by resistance coils of varying

Influence, Electric.
Electric induction, which may be either electrostatic, current, or

Insolation, Electric.
Exposure to powerful arc-light produces effects resembling those of
sun-stroke. The above term or the term "electric sun-stroke" has been
applied to them.

[Transcriber's note: Operators of arc welders are prone to skin cancer
from ultra violet rays if not properly protected.]

The entire apparatus, buildings and appurtenances of a technical or
manufacturing establishment. An electric light installation, for
instance, would include the generating plant, any special buildings, the
mains and lamps.

Insulating Stool.
A support for a person, used in experiments with static generators. It
has ordinarily a wooden top and glass legs. It separates one standing on
it from the earth and enables his surface to receive an electrostatic
charge. This tends to make his hair stand on end, and anyone on the
floor who touches him will receive a shock.

Insulating Tape.
Prepared tape used in covering the ends of wire where stripped for
making joints. After the stripped ends of two pieces are twisted
together, and if necessary soldered and carefully cleaned of soldering
fluid, they may be insulated by being wound with insulating tape.

The tape is variously prepared. It may be common cotton or other tape
saturated with any insulating compound, or may be a strip of gutta
percha or of some flexible cement-like composition.


Insulating Varnish.
Varnish used to coat the surface of glass electrical apparatus, to
prevent the deposition of hygrometric moisture, and also in the
construction of magnetizing and induction coils and the like. Shellac
dissolved in alcohol is much used. Gum copal dissolved in ether is
another. A solution of sealing wax in alcohol is also used. If applied
in quantities these may need baking to bring about the last drying. (See
Shellac Varnish.)

(a) Any insulating substance.

(b) A telegraph or line insulator for telegraph wires. (See Insulator,
Line or Telegraph.)


Insulator Cap.
A covering or hood, generally of iron, placed over an insulator to
protect it from injury by fracture with stones or missiles.

Insulator, Fluid.
(a) For very high potentials, as in induction coils or alternating
circuits, fluid insulators, such as petroleum or resin oil, have been
used. Their principal merit is that if a discharge does take place
through them the opening at once closes, so that they are self-healing.

(b) Also a form of telegraph or line insulator in which the lower rim is
turned up and inwards, so as to form an annular cup which is filled with

Insulator, Line or Telegraph.
A support often in the shape of a collar or cap, for a telegraph or
other wire, made of insulating material. Glass is generally used in the
United States, porcelain is adopted for special cases; pottery or stone
ware insulators have been used a great deal in other countries.
Sometimes the insulator is an iron hook set into a glass screw, which is
inserted into a hole in a telegraph bracket. Sometimes a hook is caused
to depend from the interior of an inverted cup and the space between the
shank of the hook and cup is filled with paraffine run in while melted.

Insulators are tested by measuring their resistance while immersed in a
vessel of water.

Intensity. Strength.
The intensity of a current or its amperage or strength; the intensity or
strength of a magnetic field or its magnetic density; the intensity or
strength of a light are examples of its use. In the case of dynamic
electricity it must be distinguished from tension. The latter
corresponds to potential difference or voltage and is not an attribute
of current; intensity has no reference to potential and is a
characteristic of current.

Intensity of a Magnetic Field.
The intensity of a magnetic field at any point is measured by the force
with which it acts on a unit magnet pole placed at that point. Hence
unit intensity of field is that intensity of field which acts on a unit
pole with a force of one dyne. (S. P. Thomson.) (See Magnetic Lines of


Crossing a pair of conductors of a metallic circuit from side to side to
avoid induction from outside sources.

Acting at intervals, as an intermittent contact, earth, or grounding of
a telegraph wire.

Interpolar Conductor.
A conductor connecting the two poles of a battery or current generator;
the external circuit in a galvanic circuit.

A process used in getting a closer approximation to the truth from two
varying observations, as of a galvanometer. The process varies for
different cases, but amounts to determining an average or deducing a
proportional reading from the discrepant observed ones.

A circuit breaker. It may be operated by hand or be automatic. (See
Circuit Breaker--Circuit Breaker, Automatic--and others.)

Interrupter, Electro-magnetic, for a Tuning Fork.
An apparatus for interrupting a current which passes through an
electromagnet near and facing one of the limbs of a tuning fork. The
circuit is made and broken by the vibrations of another tuning fork
through which the current passes. The second one is thus made to
vibrate, although it may be very far off and may not be in exact unison
with the first. The first tuning fork has a contact point on one of its
limbs, to close the circuit; it may be one which dips into a mercury

Intrapolar Region.
A term in medical electricity, denoting the part of a nerve through
which a current is passing.

The products of decomposition produced in any given electrolysis are
termed ions, the one which appears at the anode or negative electrode is
the anion. The electrode connected to the carbon or copper plate of a
wet battery is an anode. Thus in the electrolysis of water oxygen is the
anion and hydrogen is termed the kation. In this case both anion and
kation are elements. In the decomposition of copper sulphate the anion
is properly speaking sulphion (S O4), a radical, and the kation is
copper, an element. Electro-negative elements or radicals are anions,
such as oxygen, sulphion, etc., while electro-positive ones are kations,
such as potassium. Again one substance may be an anion referred to one
below it and a kation referred to one above it, in the electro-chemical
series, q. v. Anion means the ion which goes to the anode or positive
electrode; kation, the ion which goes to the kathode or negative

[Transcriber's note: An ion is an atom or molecule that has lost or
gained one or more valence electrons, giving it a positive or negative
electrical charge. A negatively charged ion, with more electrons than
protons in its nuclei, is an anion. A positively charged ion, with fewer
electrons than protons, is a cation. The electron was discovered five
years after this publication.]


A metal; one of the elements; symbol, Fe; atomic weight, 56;
equivalent, 28 and 14, ; valency, 4 and 2.
It is a conductor of electricity. The following data are at
0° C. 32° F., with annealed metal.

  Specific Resistance,   9.716 microhms.
  Relative Resistance.   6.460
  Resistance of a wire,
  (a) 1 foot long weighing 1 grain,      1.085   ohms.
  (b) 1 foot long 1/1000 inch thick,    58.45     "
  (c) 1 meter long weighing 1 gram,       .7570   "
  (d) 1 meter long, 1 millimeter thick,   .1237   "
Percentage increase in resistance per degree C. (1.8° F.)
  at about 20° C. (68°F.), about 0.5 per cent.
Resistance of a 1 inch cube,   3.825 microhms.
Electro-chemical equivalent (Hydrogen = .0105), .147 and .294

Iron, Electrolytic.
Iron deposited by electrolytic action. Various baths are employed for
its formation. (See Steeling.) It has very low coercive power, only
seven to ten times that of nickel.

Ironwork Fault of a Dynamo.
A short circuiting of a dynamo by, or any connection of its coils with,
the iron magnet cores or other iron parts.

Equality of periodic time; as of the times of successive beats of a
tuning fork, or of the times of oscillations of a pendulum.

Isoclinic Lines.
The lines denoting the locus of sets of equal dips or inclinations of
the magnetic needle upon the earth's surface, the magnetic parallels, q.
v. These lines are very irregular. (See Magnetic Elements.)

Isoclinic Map.
A map showing the position of isoclinic lines.

Isodynamic Lines.
Lines marking the locus of places of equal magnetic intensity on the
earth's surface. (See Magnetic Elements, Poles of Intensity.)

Isodynamic Map.
A map showing the position of isodynamic lines. (See Poles of

Isogonic Lines.
Lines on a map marking the locus of or connecting those points where the
declination or variation of the magnetic needle is the same. (See
Magnetic Elements--Declination of Magnetic Needle.)

Synonyms--Isogonal Lines--Halleyan Lines.


Isogonic Map.
A map showing the isogonic lines. On such a map each line is
characterized and marked with the degrees and direction of variation of
the compass upon itself.

Synonym--Declination Map.

[Transcriber's note: The file Earth_Declination_1590_1990.gif provided
by the U.S. Geological Survey ( is an animation of
the declination of the entire earth.]

Isolated Plant, Distribution or Supply.
The system of supplying electric energy by independent generating
systems, dynamo or battery, for each house, factory or other place, as
contra-distinguished from Central Station Distribution or Supply.


(Greek, equal in manner.)

Having equal properties in all directions; the reverse of anisotropic,
q. v. Thus a homogeneous mass of copper or silver has the same specific
resistance in all directions and is an isotropic conductor. Glass has
the same specific inductive capacity in all directions and is an
isotropic medium or dielectric. The same applies to magnetism. Iron is
an isotropic paramagnetic substance. (See Anisotropic.) The term applies
to other branches of physics also.

I. W. G.
Contraction for Indian Wire Gauge--the gauge adopted in British India.


Symbol for the unit joule, the unit of electric energy.

Jacobi's Law.
A law of electric motors. It states that the maximum work of a motor is
performed when the counter-electromotive force is equal to one-half the
electro-motive force expended on the motor.

Small incandescent lamps are sometimes mounted as articles of jewelry in
scarf-pins or in the hair. They may be supplied with current from
storage or from portable batteries carried on the person.

Joint, American Twist.
A joint for connecting telegraph wires, especially aerial lines. Its
construction is shown in the cut. The end of each wire is closely wound
around the straight portion of the other wire for a few turns.



Joint, Britannia.
A joint for uniting the ends of telegraph and electric wires. The ends
of the wires are scraped clean and laid alongside each other for two
inches, the extreme ends being bent up at about right angles to the
wire. A thin wire is wound four or five times around one of the wires,
back of the joint, the winding is then continued over the lapped
portion, and a few more turns are taken around the other single wire.
The whole is then soldered.


Joint, Butt.
A joint in belting or in wire in which the ends to be joined are cut off
square across, placed in contact and secured. It ensures even running
when used in belting. Any irregularity in thickness of a belt affects
the speed of the driven pulley. As dynamos are generally driven by
belts, and it is important to drive them at an even speed to prevent
variations in the electro-motive force, butt joints should be used on
belting for them, unless a very perfect lap joint is made, which does
not affect either the thickness or the stiffness of the belt.

When a butt joint is used in wire a sleeve may be used to receive the
abutting ends, which may be secured therein by soldering. This species
of joint has been used on lightning rods and may more properly be termed
a sleeve joint.

Joint, Lap.
(a) In belting a joint in which the ends are overlapped, and riveted or
otherwise secured in place. If made without reducing the thickness of
the ends it is a bad joint for electrical work, as it prevents even
running of machinery to which it is applied. Hence dynamo belts should
be joined by butt joints, or if by lap joints the ends should be shaved
off so that when joined and riveted, there will be no variation in the
thickness of the belt.

(b) In wire lap joints are made by overlapping the ends of the wire and
soldering or otherwise securing. The Britannia joint (see Joint,
Britannia,) may be considered a lap-joint.

Joint, Marriage.
A joint for stranded conductors used for Galende's cables. It is made
somewhat like a sailor's long splice. Each one of the strands is wound
separately into the place whence the opposite strand is unwound and the
ends are cut off so as to abutt. In this way all are smoothly laid in
place and soldering is next applied.



Joint, Sleeve.
A joint in electric conductors, in which the ends of the wires are
inserted into and secured in a metallic sleeve or tube, whose internal
diameter is just sufficient to admit them.

Joint, Splayed.
The method of joining the ends of stranded conductors. The insulating
covering is removed, the wires are opened out, and the center wire,
heart or core of the cable is cut off short. The two ends are brought
together, the opened out wires are interlaced or crotched like the
fingers of the two hands, and the ends are wound around the body of the
cable in opposite directions. The joint is trimmed and well soldered.
Tinned wire with rosin flux for the soldering is to be recommended.
Insulating material is finally applied by hand, with heat if necessary.

Joints in Belts.
Belt-joints for electric plants where the belts drive dynamos should be
made with special care. The least inequality affects the electro-motive
force. Butt joints are, generally speaking, the best, where the ends of
the belt are placed in contact and laced. Lap-joints are made by
overlapping the belt, and unless the belt is carefully tapered so as to
preserve uniform strength, the speed of the dynamo will vary and also
the electromotive force.

A name proposed to be substituted for "joule," q. v. It has not been

This term has been applied to several units.

(a) The practical C. G. S. unit of electric energy and work--the
volt-coulomb. It is equal to 1E7 ergs--0.73734 foot pound.--.00134 horse
power seconds. A volt-ampere represents one joule per second.

(b) It has also been used as the name of the gram-degree C. thermal
unit--the small calorie.


Joule Effect.
The heating effect of a current passing through a conductor. It varies
with the product of the resistance by the square of the current, or with

Joule's Equivalent.
The mechanical equivalent of heat, which if stated in foot-pounds per
pound-degree F. units, is 772 (772.55). (See Equivalents.)

Junction Box.
In underground distribution systems, an iron casing or box in which the
feeders and mains are joined, and where other junctions are made.

Synonym--Fishing Box.


The symbol for electrostatic capacity.

A product of decomposition of feldspar, consisting approximately of
silica, 45, alumina, 40, water, 15. It was used in electric candles of
the Jablochkoff type as a constituent of the insulating layer or
colombin. Later it was abandoned for another substance, as it was found
that it melted and acted as a conductor.


Kapp Line of Force.
A line of force proposed by Kapp. It is equal to 6,000 C. G. S. lines of
force, and the unit of area is the square inch. Unfortunately it has
been adopted by many manufacturers, but its use should be discouraged,
as it is a departure from the uniform system of units.

One Kapp line per square inch = 930 C. G. S. lines per square

A term used in medical electricity or electro-therapeutics to indicate
the increased functional activity induced in a nerve by the proximity of
the kathode of an active circuit which is completed through the nerve.
The converse of anelectrotonus.

The terminal of an electric circuit whence an electrolyzing current
passes from a solution. It is the terminal connected to the zinc plate
of a primary battery.

Kathodic Closure Contraction.
A term in electro-therapeutics; the contractions near where the kathode
of an active circuit is applied to the body, which are observed at the
instant when the circuit is closed.

Kathodic Duration Contraction.
A term in electro-therapeutics; the contraction near where the kathode
of an active circuit is applied to the body for a period of time.

K. C. C.
Abbreviation for Kathodic Closure Contraction, q. v.

K. D. C.
Abbreviation for Kathodic Duration Contraction, q. v.

A bar of soft iron used to connect the opposite poles of a horseshoe
magnet or the opposite poles of two bar magnets placed side by side. It
is designed to prevent loss of magnetism. The armature of a horseshoe
magnet is generally used as its keeper. For bar magnets a keeper is used
for each end, the magnets being laid side by side, with their poles in
opposite direction but not touching, and a keeper laid across at each
end connecting the opposite poles.

Kerr Effect.
The effect of an electrostatic field upon polarized light traversing a
dielectric contained within the field. (See Electrostatic Refraction.)

Kerr's Experiment.
Polarized light reflected from the polished face of a magnet pole has
its plane of polarization rotated; when it is reflected from the north
pole the rotation is from left to right.


A switch adapted for making and breaking contact easily when worked by
hand, as a Morse telegraph key.

Key Board.
A board or tablet on which keys or switches are mounted.

(a) A switch board, q. v.

(b) A set of lettered keys similar to those of a typewriter employed in
some telegraph instruments. As each key is depressed it produces the
contact or break requisite for the sending of the signal corresponding
to the letter marked upon the key. The signal in printing telegraphs, on
which such key-boards are used, is the reprinting of the letter at the
distant end of the line.

Key, Bridge.
A key for use with a Wheatstone Bridge, q.v. It is desirable to first
send a current through the four arms of the bridge in using it for
testing resistances and then through the galvanometer, because it takes
a definite time for the current to reach its full strength. This is
especially the case if the element being measured has high static
capacity, as a long ocean cable. If the galvanometer connections were
completed simultaneously with the bridge connections a momentary swing
would be produced even if the arms bore the proper relation to each
other. This would cause delay in the testing. A bridge key avoids this
by first connecting the battery circuit through the arms of the bridge,
and then as it is still further depressed the galvanometer circuit is



Key, Charge and Discharge.
A key for use in observing the discharge of a condenser immediately
after removing the battery. In one typical form it has two contacts, one
below and one above, and being a spring in itself is pressed up against
the upper one. Connections are so made that when in its upper position
it brings the two coatings of the condenser in circuit with the
galvanometer. When depressed it does the same for a battery. In use it
is depressed and suddenly released when the galvanometer receives the
full charge, before there has been time for leakage. This is one method
of connection illustrating its principle.

In the cut L is the spring-key proper. S2, is the upper contact screw
against which the spring normally presses. In this position the
galvanometer G is in circuit with the opposite coatings of the condenser
C. On depressing the contact S2, is broken and S1, is made. This brings
the battery B in circuit with the condenser coatings. On releasing the
key it springs up and the galvanometer receives the effect of the charge
of the condenser as derived from the battery.

Key, Double Contact.
A key arranged to close two distinct circuits, holding the first closed
until the second is completed. It is used for Wheatstone bridge work.

Key, Double Tapper.
A telegraph key giving contacts alternately for currents in opposite
directions, used in needle telegraphy.

Key, Increment.
A key for use in duplex and quadruplex telegraphy. Its action is to
increase the line current, not merely to suddenly turn current into it.



Key, Kempe's Discharge.
A key giving a charging, discharging and insulating connection, for
static condenser work. Referring to the cut l is a lever or spring with
upper discharging contact s, and lower charging contact s'. In use it is
pressed down by the insulating handle or finger piece C, until caught by
the hook attached to the key I. This hook is lower down than that on the
key D, and holds it in contact with the charging contact piece S'. On
pressing the key I, marked or designated "Insulate," it springs up,
breaks contact at S', and catching against the hook on D, which key is
designated "Discharge," remains insulated from both contacts; next on
pressing D it is released and springs up and closes the discharge
contact S. It is a form of charge and discharge key. (See Key, Charge
and Discharge.)

Key, Magneto-electric.
A telegraph key whose movements operate what is virtually a small
magneto-generator, so as to produce currents of alternating direction,
one impulse for each motion of the key. It is employed for telegraphing
without a line battery, a polarized relay being used. In one very simple
form a key is mounted on a base with a permanent magnet and connected to
the armature, so that when the key is pressed downwards it draws the
armature away from the poles of the magnet. If the magnet or its
armature is wound with insulated wire this action of the key will cause
instantaneous currents to go through a circuit connected to the magnet
or armature coils.


In Siemens & Halske's key an H armature E is pivoted between the poles N
S, of a powerful compound horseshoe magnet, G G. It is wound with fine
wire and a key handle H is provided for working it. In its normal
position the handle is drawn upward, and the end S S of the armature
core is in contact with the south pole S of the permanent magnet, and
the end D D with the north pole. This establishes the polarity of the
armature. On depressing the key the contacts are broken and in their
place the end D D comes in contact with the south pole and the end S S
with the north pole. This suddenly reverses the polarity of the armature
and sends a momentary current through the armature coil which is in
circuit with the line. The cut only shows the principle of the key,
whose construction is quite complicated.


Key, Make and Break.
An ordinary electric key, usually making a contact when depressed, and
rising by spring action when released, and in its rise breaking the

Fig. 209. PLUG KEY

Key, Plug.
An appliance for closing a circuit. Two brass blocks are connected to
the terminals, but are disconnected from each other. A brass plug
slightly coned or with its end split so as to give it spring action is
thrust between the blocks to complete the circuit. It is used in
Resistance coils and elsewhere. (See Coil, Resistance.) Grooves are
formed in the blocks to receive the plug.

Key, Reversing.
(a) A double key, arranged so that by depressing one key a current flows
in one direction, and by depressing the other a current flows in the
opposite direction. It is used in connection with a galvanometer in
experimental, testing or measuring operations.

(b) A key effecting the same result used in quadruplex telegraphy.

Key, Sliding-Contact.
A name given to the key used for making instantaneous contacts with the
metre wire of a metre bridge, q. v. The name is not strictly correct,
because it is important that there should be no sliding contact made, as
it would wear out the wire and make it of uneven resistance.

It is a key which slides along over the wire and which, when depressed,
presses a platinum tipped knife edge upon the wire. On being released
from pressure the key handle springs up and takes the knife edge off the
wire. This removal is essential to avoid wearing the wire, whose
resistance per unit of length must be absolutely uniform.

Key, Telegraph.
The key used in telegraphy for sending currents as desired over the
line. It consists of a pivoted lever with finger piece, which lever when
depressed makes contact between a contact point on its end and a
stationary contact point on the base. This closes the circuit through
the line. When released it springs up and opens the line circuit.

A prefix to the names of units; it indicates one thousand times, as
kilogram, one thousand grams. A few such units are given below.

A compound unit; one thousand dynes. (See Dyne.)

A compound unit; one thousand grams; 2.2046 pounds avds.


A compound unit; one thousand joules, q. v.

A compound unit; one thousand meters; 3280.899 feet; 0.621382 statute
miles. (See Meter.)

A compound unit; one thousand watts, q. v.

An absolute or C. G. S. unit of velocity or rate of motion; one
centimeter per second; proposed by the British Association.

Kirchoff's Laws.
These relate to divided circuits.

I. When a steady current branches, the quantity of electricity arriving
by the single wire is equal to the quantity leaving the junction by the
branches. The algebraical sum of the intensities of the currents passing
towards (or passing from) the junction is equal to zero; Summation(C) =
0 (Daniell.) In the last sentence currents flowing towards the point are
considered of one sign and those flowing away from it of the other.

II. In a metallic circuit comprising within it a source of permanent
difference of potential, E, the products of the intensity of the current
within each part of the circuit into the corresponding resistance are,
if the elements of current be all taken in cyclical order together,
equal to E; Summation(C * r) =E. In a metallic circuit in which there is
no source of permanent difference of potential E = 0, and Summation(C *
r)  = 0.

This law applies to each several mesh of a wire network as well as to a
single metallic loop, and it holds good even when an extraneous current
is passed through the loop. (Daniell.)

In this statement of the two laws E stands for electro-motive force, C
for current intensity; and r for resistance of a single member of the

[Transcriber's note: These laws may be restated as: At any point in an
steady-state electrical circuit, the directed sum of currents flowing
towards that point is zero. The directed sum of the electrical potential
differences around any closed circuit is zero.]

Knife-edge Suspension.
The suspension of an object on a sharp edge of steel or agate. The knife
edge should abut against a plane. The knife edge is generally carried by
the poised object. Its edge then faces downward and on the support one
or more plane or approximately plane surfaces are provided on which it
rests. In the ordinary balance this suspension can be seen. It is
sometimes used in the dipping needle.

It is applied in cases where vertical oscillations are to be provided

The geographical mile; a term derived from the knots on the log line,
used by navigators. It is equal to 6,087 feet.

Synonyms--Nautical Mile--Geographical Mile.

[Transcriber's note: A knot is a velocity, 1 nautical mile per hour, not
a distance. The contemporary definition is: 1 international knot = 1
nautical mile per hour = 1.852 kilometres per hour = 1.1507794 miles per
hour = 0.51444444 meters per second = 6076.1152 feet per hour.]


Kohlrausch's Law.
A law of the rate of travel of the elements and radicals in solutions
under the effects of electrolysis. It states that each element under the
effects of electrolysis has a rate of travel for a given liquid, which
is independent of the element with which it was combined. The rates of
travel are stated for different elements in centimeters per hour for a
potential difference of one or more volts per centimeter of path.

[Friedrich Wilhelm Georg Kohlrausch (1840-1910)]

Kookogey's Solution.
An acid exciting and depolarizing solution for a zinc-carbon couple,
such as a Bunsen battery. Its formula is: Potassium bichromate, 227
parts; water, boiling, 1,134 parts; while boiling add very carefully and
slowly 1,558 parts concentrated sulphuric acid. All parts are by weight.
Use cold.

Krizik's Cores.
Cores of iron for use with magnetizing coils, q. v. They are so shaped,
the metal increasing in quantity per unit of length, as the centre is
approached, that the pull of the excited coil upon them will as far as
possible be equal in all positions. A uniform cylinder is attracted with
varying force according to its position; the Krizik bars or cores are
attracted approximately uniformly through a considerable range.


Symbol for length and also for the unit of inductance or coefficient of
induction, because the dimensions of inductance are length.

Lag, Angle of.
(a) The angle of displacement of the magnetic axis of an armature of a
dynamo, due to its magnetic lag. The axis of magnetism is displaced in
the direction of rotation. (See Magnetic Lag.)

(b) The angle expressing the lag of alternating current and
electro-motive force phases.

Laminated. adj.
Made up of thin plates, as a laminated armature core or converter core.

The building up of an armature core or other thing out of plates. The
cores of dynamo armatures or of alternating current converters are often
laminated. Thus a drum armature core may consist of a quantity of thin
iron discs, strung upon a rod and rigidly secured, either with or
without paper insulation between the discs. If no paper is used the film
of oxide on the iron is relied on for insulation. The object of
lamination is to break up the electrical continuity of the core, so as
to avoid Foucault currents. (See Currents, Foucault.) The laminations
should be at right angles to the direction of the Foucault currents
which would be produced, or in most cases should be at right angles to
the active parts of the wire windings.


Lamination of Armature Conductors.
These are sometimes laminated to prevent the formation of eddy currents.
The lamination should be radial, and the strips composing it should be
insulated from each other by superficial oxidation, oiling or
enamelling, and should be united only at their ends.


Lamp, Arc.
A lamp in which the light is produced by a voltaic arc. Carbon
electrodes are almost universally employed. Special mechanism, operating
partly by spring or gravity and partly by electricity, is employed to
regulate the distance apart of the carbons, to let them touch when no
current passes, and to separate them when current is first turned on.

The most varied constructions have been employed, examples of which will
be found in their places. Lamps may in general be divided into classes
as follows, according to their regulating mechanism and other features:

(a) Single light regulators or monophotes. Lamps through whose
regulating mechanism the whole current passes. These are only adapted to
work singly; if several are placed in series on the same circuit, the
action of one regulator interferes with that of the next one.

(b) Multiple light regulators or polyphotes. In these the regulating
mechanism and the carbons with their arc are in parallel; the regulating
device may be a single magnet or solenoid constituting a derived or
shunt-circuit lamp, or it may include two magnets working differentially
against or in opposition to each other constituting a differential lamp.


(c) Lamps with fixed parallel carbons termed candles (q. v., of various

(d) Lamps without regulating mechanism. These include lamps with
converging carbons, whose object was to dispense with the regulating
mechanism, but which in some cases have about as much regulating
mechanism as any of the ordinary arc lamps.

Lamp, Contact.
A lamp depending for its action on loose contact between two carbon
electrodes. At the contact a species of incandescence with incipient
arcs is produced. One of the electrodes is usually flat or nearly so,
and the other one of pencil shape rests upon it.

Lamp, Differential Arc.
An arc lamp, the regulation of the distance between whose carbons
depends on the differential action of two separate electrical coils. The
diagram illustrates the principle. The two carbons are seen in black;
the upper one is movable, The current arrives at A. It divides, and the
greater part goes through the low resistance coil M to a contact roller
r, and thence by the frame to the upper carbon, and through the arc and
lower carbon to B, where it leaves the lamp. A smaller portion of the
current goes through the coil M1 of higher resistance and leaves the
lamp also at B. A double conical iron core is seen, to which the upper
carbon holder is attached. This is attracted in opposite directions by
the two coils. If the arc grows too long its resistance increases and
the coil M1 receiving more current draws it down and thus shortens the
arc. If the arc grows too short, its resistance falls, and the coil M
receives more current and draws the core upwards, thus lengthening the
arc. This differential action of the two cores gives the lamp its name.
R is a pulley over which a cord passes, one end attached to the core and
the other to a counterpoise weight, W.



Lamp, Holophote.
A lamp designed for use alone upon its own circuit. These have the
regulating mechanism in series with the carbon and arc, so that the
whole current goes through both. (See Lamp, Arc.)

Synonym--Monophote Lamp.

A unit of commercial supply of electric energy; the volt-coulombs
required to maintain an electric lamp for one hour. A sixteen-candle
power incandescent lamp is practically the lamp alluded to, and requires
about half an ampere current at 110 volts, making a lamp-hour equal to
about 198,000 volt-coulombs.

[Transcriber's note: 0.55 KW hours.]

Lamp, Incandescent.
An electric lamp in which the light is produced by heating to whiteness
a refractory conductor by the passage of a current of electricity. It is
distinguished from an arc lamp (which etymologically is also an
incandescent lamp) by the absence of any break in the continuity of its
refractory conductor. Many different forms and methods of construction
have been tried, but now all have settled into approximately the same

The incandescent lamp consists of a small glass bulb, called the
lamp-chamber, which is exhausted of air and hermetically sealed. It
contains a filament of carbon, bent into a loop of more or less simple
shape. This shape prevents any tensile strain upon the loop and also
approximates to the outline of a regular flame.



The loop is attached at its ends to two short pieces of platinum wire,
which pass through the glass of the bulb and around which the glass is
fused. As platinum has almost exactly the same coefficient of
heat-expansion as glass, the wires do not cause the glass to crack.

The process of manufacture includes the preparation of the filament.
This is made from paper, silk, bamboo fibre, tamidine, q. v., or other
material. After shaping into the form of the filament the material is
carbonized at a high heat, while embedded in charcoal, or otherwise
protected from the air. The flashing process (see Flashing of
incandescent Lamp Carbons) may also be applied. The attachment to the
platinum wires is effected by a minute clamp or by electric soldering.
The loop is inserted and secured within the open globe, which the glass
blower nearly closes, leaving one opening for exhaustion.

The air is pumped out, perhaps first by a piston pump, but always at the
end by a mercurial air pump. (See Pump, Geissler--and others.) As the
exhaustion becomes high a current is passed through the carbons heating
them eventually to white heat so as to expel occluded gas. The occluded
gases are exhausted by the pump and the lamp is sealed by melting the
glass with a blowpipe or blast-lamp flame. For the exhaustion several
lamps are usually fastened together by branching glass tubes, and are
sealed off one by one.

The incandescent lamps require about 3.5 watts to the candle power, or
give about 12 sixteen-candle lamps to the horse power expended on them.

Generally incandescent lamps are run in parallel or on multiple arc
circuits. All that is necessary in such distribution systems is to
maintain a proper potential difference between the two leads across
which the lamps are connected. In the manufacture of lamps they are
brought to an even resistance and the proper voltage at which they
should be run is often marked upon them. This may be fifty volts and
upward. One hundred and ten volts is a very usual figure. As current one
ampere for a fifty-volt, or about one-half an ampere for a one hundred
and ten volt lamp is employed.

Lamp, Incandescent, Three Filament.
A three filament lamp is used for three phase currents. It has three
filaments whose inner ends are connected, and each of which has one
leading-in wire. The three wires are connected to the three wires of the
circuit. Each filament receives a current varying in intensity, so that
there is always one filament passing a current equal to the sum of the
currents in the other two filaments.

Lamp, Lighthouse.
A special type of arc light. It is adapted for use in a lighthouse
dioptric lantern, and hence its arc has to be maintained in the same
position, in the focus of the lenses. The lamps are so constructed as to
feed both carbons instead of only one, thereby securing the above


Lamp, Pilot.
A lamp connected to a dynamo, and used by its degree of illumination to
show when the dynamo on starting becomes excited, or builds itself up.

Lamp, Polyphote.
An arc lamp adapted to be used, a number in series, upon the same
circuit. The electric regulating mechanism is placed in shunt or in
parallel with the carbons and arc. (See Lamp, Arc.)

Lamps, Bank of.
A number of lamps mounted on a board or other base, and connected to
serve as voltage indicator or to show the existence of grounds, or for
other purposes.

Lamp, Semi-incandescent.
A lamp partaking of the characteristics of both arc and incandescence; a
lamp in which the imperfect contact of two carbon electrodes produces a
part of or all of the resistance to the current which causes

The usual type of these lamps includes a thin carbon rod which rests
against a block of carbon. The species of arc formed at the junction of
the two heats the carbons. Sometimes the upper carbon or at least its
end is heated also by true incandescence, the current being conveyed
near to its end before entering it.

Semi-incandescent lamps are not used to any extent now.

Lamp Socket.
A receptacle for an incandescent lamp; the lamp being inserted the
necessary connections with the two leads are automatically made in most
sockets. The lamps may be screwed or simply thrust into the socket and
different ones are constructed for different types of lamps. A key for
turning the current on and off is often a part of the socket.

Latent Electricity.
The bound charge of static electricity. (See Charge, Bound.)

Law of Intermediate Metals.
A law of thermo-electricity. The electro-motive force between any two
metals is equal to the sum of electro-motive forces between each of the
two metals and any intermediate metal in the thermo-electric series, or
the electro-motive force between any two metals is equal to the sum of
the electromotive forces between all the intermediate ones and the
original two metals; it is the analogue of Volta's Law, q. v.

Law of Inverse Squares.
When force is exercised through space from a point, its intensity varies
inversely with the square of the distance. Thus the intensity of light
radiated by a luminous point at twice a given distance therefrom is of
one-fourth the intensity it had at the distance in question.
Gravitation, electric and magnetic attraction and repulsion and other
radiant forces are subject to the same law.


Law of Successive Temperatures.
A law of thermo-electricity. The electro-motive force due to a given
difference of temperature between the opposite junctions of the metals
is equal to the sum of the electro-motive forces produced by fractional
differences of temperature, whose sum is equal to the given difference
and whose sum exactly fills the given range of temperature.

Law, Right-handed Screw.
This rather crude name is given by Emtage to a law expressing the
relation of direction of current in a circuit to the positive direction
of the axis of a magnet acted on by such current. It is thus expressed:
A right-handed screw placed along the axis of the magnet and turned in
the direction of the current will move in the positive direction, i. e.,
towards the north pole of the axis of the magnet.

A metal; one of the elements; symbol Pb. Atomic weight, 207;
equivalent, 103-1/2; valency, 2.
Lead may also be a tetrad, when its equivalent is 51.75.
The following data are at 0º C. (32º F.) with compressed metal:
Relative Resistance, (Silver = l)     13.05
Specific Resistance,                  19.63   microhms.
Resistance of a wire,
(a) 1 ft. long, weighing 1 grain,       3.200   ohms.
(b) 1 meter long, weighing 1 gram,      2.232  "
(c) 1 meter long, 1 millimeter thick,    .2498  "
Resistance of 1 inch cube,              7.728   microhms.
Electro-Chemical Equivalent (Hydrogen = .0105)   1.086   mgs.

Leading Horns.
The tips of pole pieces in a dynamo, which extend in the direction of
movement of the armature.

Leading-in Wires.
The platinum wires passing through the glass of an incandescent
lamp-chamber, to effect the connection of the carbon filament with the
wires of the circuit.

Lead of Brushes, Negative.
In a motor the brushes are set backwards from their normal position, or
in a position towards the direction of armature rotation or given a
negative lead instead of a positive one, such as is given to dynamo

A loss or escape of electricity by accidental connection either with the
ground or with some conductor. There are various kinds of leak to which
descriptive terms are applied.

The loss of current from conductors; due to grounding at least at two
places, or to very slight grounding at a great many places, or all along
a line owing to poor insulation. In aerial or pole telegraph lines in
wet weather there is often a very large leakage down the wet poles from
the wire. (See Surface Leakage--Magnetic Leakage.)


Leakage Conductor.
A conductor placed on telegraph poles to conduct directly to earth any
leakage from a wire and thus prevent any but a very small portion
finding its way into the other wires on the same pole. It presents a
choice of evils, as it increases the electrostatic capacity of the line,
and thus does harm as well as good. It consists simply of a wire
grounded and secured to the pole.

Leg of Circuit.
One lead or side of a complete metallic circuit.

Lenz's Law.
A law expressing the relations of direction of an inducing current or
field of force to the current induced by any disturbance in the
relations between such field and any closed conductor within its
influence. It may be variously expressed.

(a) If the relative position of two conductors, A and B, be changed, of
which A is traversed by a current, a current is induced in B in such a
direction that, by its electro-dynamic action on the current in A, it
would have imparted to the conductors a motion of the contrary kind to
that by which the inducing action was produced. (Ganot.)

(b) The new (induced) current will increase the already existing
resistances, or develop new resistance to that disturbance of the field
which is the cause of induction. (Daniell.)

(c) When a conductor is moving in a magnetic field a current is induced
in the conductor in such a direction as by its mechanical action to
oppose the motion. (Emtage.)

(d) The induced currents are such as to develop resistance to the change
brought about.

Letter Boxes, Electric.
Letter boxes with electrical connections to a bell or indicator of some
sort, which is caused to act by putting a letter into the box.

Leyden Jar.
A form of static condenser.

In its usual form it consists of a glass jar. Tinfoil is pasted around
the lower portions of its exterior and interior surfaces, covering from
one-quarter to three-quarters of the walls in ordinary examples. The
rest of the glass is preferably shellacked or painted over with
insulating varnish, q. v. The mouth is closed with a wooden or cork
stopper and through its centre a brass rod passes which by a short chain
or wire is in connection with the interior coating of the jar. The top
of the rod carries a brass knob or ball.

If such a jar is held by the tinfoil-covered surface in one hand and its
knob is held against the excited prime conductor of a static machine its
interior becomes charged; an equivalent quantity of the same electricity
is repelled through the person of the experimenter to the earth and when
removed from the conductor it will be found to hold a bound charge. If
the outer coating and knob are both touched or nearly touched by a
conductor a disruptive discharge through it takes place.



If one or more persons act as discharging conductors they will receive a
shock. This is done by their joining hands, a person at one end touching
the outer coating and another person at the other end touching the knob.

From an influence machine a charge can be taken by connecting the
coating to one electrode and the knob to the other.



Leyden Jar, Sir William Thomson's.
An especially efficient form of Leyden jar. It consists of a jar with
outer tinfoil coating only. For the interior coating is substituted a
quantity of concentrated sulphuric acid. The central rod is of lead with
a foot, which is immersed in the acid and from which the rod rises. A
wooden cover partly closes the jar, as the central tube through which
the rod passes is so large as not to allow the wood to touch it. Thus
any leakage from inner to outer coating has to pass over the inside and
outside glass surfaces. In the common form of jar the wooden cover may
short circuit the uncoated portion of the inner glass surface. In the
cut a simplified form of Thomson's Leyden jar is shown, adapted for
scientific work.

Lichtenberg's Figures.
If the knob of a Leyden jar or other exited electrode is rubbed over the
surface of ebonite, shellac, resin or other non-conducting surface it
leaves it electrified in the path of the knob. If fine powder such as
flowers of sulphur or lycopodium is dusted over the surface and the
excess is blown away, the powder will adhere where the surface was
electrified, forming what are called Lichtenberg's Figures, Lycopodium
and sulphur show both positive and negative figures, that is to say,
figures produced by a positively or negatively charged conductor. Red
lead adheres only to negative figures. If both positive and negative
figures are made and the surface is sprinkled with both red lead and
flowers of sulphur each picks out its own figure, the sulphur going
principally to the positive one.

The red lead takes the form of small circular heaps, the sulphur
arranges itself in tufts with numerous diverging branches. This
indicates the difference in the two electricities. The figures have been
described as "a very sensitive electrosope for investigating the
distribution of electricity on an insulating surface." (Ganot.)

Life of Incandescent Lamps.
The period of time a lamp remains in action before the carbon filament
is destroyed. The cause of a lamp failing may be the volatilization of
the carbon of the filament, causing it to become thin and to break; or
the chamber may leak. The life of the lamp varies; 600 hours is a fair
estimate. Sometimes they last several times this period.

The higher the intensity at which they are used the shorter is their
life. From their prime cost and the cost of current the most economical
way to run them can be approximately calculated.

[Transcriber's note: Contemporary incandecent buls are rated for 1000
hours; flourescent bulbs up to 24000 hours; LED lamps up to 100000 hours.]

The electrostatic discharge to the earth or among themselves of clouds
floating in the atmosphere. The discharge is accompanied by a spark or
other luminous effect, which may be very bright and the effects, thermal
and mechanical, are often of enormous intensity.

The lightning flash is white near the earth, but in the upper regions
where the air is rarefied it is of a blue tint, like the spark of the
electric machine. The flashes are often over a mile in length, and
sometimes are four or five miles long. They have sometimes a curious
sinuous and often a branching shape, which has been determined by
photography only recently. To the eye the shape seems zigzag.


In the case of a mile-long flash it has been estimated that 3,516,480 De
la Rue cells, q. v., would be required for the development of the
potential, giving the flash over three and one-half millions of volts.
But as it is uncertain how far the discharge is helped on its course by
the rain drops this estimate may be too high.

There are two general types of flash. The so-called zigzag flash
resembles the spark of an electric machine, and is undoubtedly due to
the disruptive discharge from cloud to earth. Sheet lightning has no
shape, simply is a sudden glow, and from examination of the spectrum
appears to be brush discharges (see Discharge, Brush) between clouds.
Heat lightning is attributed to flashes below the horizon whose light
only is seen by us. Globe or ball lightning takes the form of globes of
fire, sometimes visible for ten seconds, descending from the clouds. On
reaching the earth they sometimes rebound, and sometimes explode with a
loud detonation. No adequate explanation has been found for them.

The flash does not exceed one-millionth of a second in duration; its
absolute light is believed to be comparable to that of the sun, but its
brief duration makes its total light far less than that of the sun for
any period of time.

If the disruptive discharge passes through a living animal it is often
fatal. As it reaches the earth it often has power enough to fuse sand,
producing fulgurites, q. v. (See also Back Shock or Stroke of

Volcanic lightning, which accompanies the eruptions of volcanoes, is
attributed to friction of the volcanic dust and to vapor condensation.

[Transcriber's note: The origin of lightning is still (2008) not fully
understood, but is thought to relate to charge separation in the
vertical motion of water droplets and ice crystals in cloud updrafts. A
lightning bolt carries a current of 40,000 to 120,000 amperes, and
transfers a charge of about five coulombs. Nearby air is heated to about
10,000 °C (18,000 °F), almost twice the temperature of the Sun’s

Lightning Arrester.
An apparatus for use with electric lines to carry off to earth any
lightning discharge such lines may pick up. Such discharge would imperil
life as well as property in telegraph offices and the like.

Arresters are generally constructed on the following lines. The line
wires have connected to them a plate with teeth; a second similar plate
is placed near this with its teeth opposite to those of the first plate
and nearly touching it. The second plate is connected by a low
resistance conductor to ground. Any lightning discharge is apt to jump
across the interval, of a small fraction of an inch, between the
oppositely placed points and go to earth.

Another type consists of two plates, placed face to face, and pressing
between them a piece of paper or mica. The lightning is supposed to
perforate this and go to earth. One plate is connected to the line, the
other one is grounded.

The lightning arrester is placed near the end of the line before it
reaches any instrument. (See Alternative Paths.)




Lightning Arrester, Counter-electro-motive Force.
An invention of Prof. Elihu Thompson. A lightning arrester in which the
lightning discharge sets up a counter-electro-motive force opposed to
its own. This it does by an induction coil. If a discharge to earth
takes place it selects the primary of the coil as it has low
self-induction. In its discharge it induces in the secondary a reverse
electro-motive force which protects the line.

Lightning Arrester Plates.
The toothed plates nearly in contact, tooth for tooth, or the flat
plates of a film lightning arrester, which constitute a lightning
arrester. Some advocate restricting the term to the plate connected to
the line.

Lightning Arrester, Vacuum.
A glass tube, almost completely exhausted, into which the line wire is
fused, while a wire leading to an earth connection has its end fused in

A high tension discharge, such as that of lightning, goes to earth
across the partial vacuum in preference to going through the line, which
by its capacity and self-induction opposes the passage through it of a
lightning discharge.

It is especially adapted for underground and submarine lines.


Lightning, Ascending.
Lightning is sometimes observed which seems to ascend. It is thought
that this may be due to positive electrification of the earth and
negative electrification of the clouds.

Lightning, Globe or Globular.
A very unusual form of lightning discharge, in which the flashes appear
as globes or balls of light. They are sometimes visible for ten seconds,
moving so slowly that the eye can follow them. They often rebound on
striking the ground, and sometimes explode with a noise like a cannon.
They have never been satisfactorily explained. Sometimes the phenomenon
is probably subjective and due to persistence of vision.

Lightning Jar.
A Leyden jar whose coatings are of metallic filings dusted on to the
surface while shellacked, and before the varnish has had time to dry. In
its discharge a scintillation of sparks appears all over the surface.

Line of Contact.
The line joining the points of contact of the commutator brushes in a
dynamo or motor.

Synonym--Diameter of Commutation.

Lines of Force.
Imaginary lines denoting the direction of repulsion or attraction in a
field of force, q. v. They may also be so distributed as to indicate the
relative intensity of all different parts of the field. They are normal
to equipotential surfaces. (See Electro-magnetic Lines of
Force--Electrostatic Lines of Force--Magnetic Lines of Force.)

Lines of Induction.
Imaginary lines within a body marking the direction taken within it by
magnetic induction. These are not necessarily parallel to lines of
force, but may, in bodies of uniform agglomeration, or in crystalline
bodies, take various directions.

Synonym--Lines of Magnetic Induction.

Lines of Slope.
Lines in a field of force which mark the directions in which the
intensity of force in the field most rapidly falls away.

Links, Fuse.
Links made of more or less easily fusible metal, for use as safety

Listening Cam.
In a telephone exchange a cam or species of switch used to connect the
operator's telephone with a subscriber's line.


A block of compressed lead binoxide, with platinum connecting foils for
use as an electrode in a storage battery. It has considerable capacity,
over 5 ampere-hours per pound of plates, but has not met with any
extended adoption.

In a dynamo the amperes of current delivered by it under any given

Local Action.
(a) In its most usual sense the electric currents within a battery, due
to impurities in the zinc, which currents may circulate in exceedingly
minute circuits, and which waste zinc and chemicals and contribute
nothing to the regular current of the battery. Amalgamated or chemically
pure zinc develops no local action.

(b) The term is sometimes applied to currents set up within the armature
core or pole pieces of a dynamo. (See Currents, Foucault.)

Local Battery.
A battery supplying a local circuit (q. v.); in telegraphy, where it is
principally used, the battery is thrown in and out of action by a relay,
and its current does the work of actuating the sounder and any other
local or station instruments. (See Relay.)

Local Circuit.
A short circuit on which are placed local apparatus or instruments. Such
circuit is of low resistance and its current is supplied by a local
battery, q. v. Its action is determined by the current from the main
line throwing its battery in and out of circuit by a relay, q. v., or
some equivalent.

Local Currents.
Currents within the metal parts of a dynamo. (See Currents, Foucault.)
In a galvanic battery. where there is local action, q. v., there are
also local currents, though they are not often referred to.

Determining the position of anything, such as a break in a cable, or a
grounding in a telegraph line. In ocean cables two typical cases are the
localization of a break in the conductor and of a defect in the
insulation admitting water. The first is done by determining the static
capacity of the portion of the line which includes the unbroken portion
of the conductor; the other by determining the resistance of the line on
a grounded circuit.

A place. The word is used to designate the locality or position of, or
series of positions of definite conditions and the like. Thus an
isogonic line is the locus of equal declinations of the magnetic needle;
it is a line passing through all places on the earth's surface where the
condition of a given declination is found to exist.


Magnetic magnetite; magnetite is an ore of iron, Fe3 04 which is
attracted by the magnet. Some samples possess polarity and attract iron.
The latter are lodestones.

Synonym--Hercules Stone

The exponent of the power to which it is necessary to raise a fixed
number to produce a given number. The fixed number is the base of the
system. There are two systems; one, called the ordinary system, has 10
for its base, the other, called the Naperian system, has 2.71828 for its
base. The latter are also termed hyperbolic logarithms, and are only
used in special calculations.

Log, Electric.
An apparatus for measuring the speed of a ship. A rotating helical vane
of known pitch is dragged behind the vessel. As the helix rotates its
movements may actuate electric machinery for registering its rotations.
The number of these in a given time, multiplied by the pitch of the
vane, gives the distance traversed in such time.

A portion of a circuit introduced in series into another circuit. The
latter circuit is opened by a spring-jack, q. v. or other device, and
the loop inserted. By loops any number of connections can be inserted
into a circuit in series therewith, and in series or in parallel with
one another.

Loop Break.
A double bracket or similar arrangement for holding on insulators the
ends of a conductor which is cut between them, and to which are
connected the ends of a loop. The space between the insulators may be
about a foot.

This may be used as the plural of lux, q. v. It is the Latin plural.

Luminous Jar.
A Leyden jar whose coatings are of lozenge-shaped pieces of tinfoil
between which are very short intervals. When discharged, sparks appear
all over the surface where the lozenges nearly join.

A standard of illumination, q. v., as distinguished from illuminating

It is the light given by one candle at a distance of 12.7 inches--by a
carcel, q. v., at a distance of one meter---or by 10,000 candles at
105.8 feet.

It was proposed by W. H. Preece. All the above valuations are identical.


(a) Symbol of gaseous pressure equal to one-millionth of an atmosphere.

(b) The Greek m, µ, is used as the symbol of magnetic permeability.


Machine, Cylinder Electric.
A frictional electric machine whose rotating glass is in the shape of a
cylinder instead of a disc as in the more recent machines.


Machine, Frictional Electric.
An apparatus for development of high tension electricity by contact
action, brought about by friction.

It consists of a plate or cylinder of glass mounted on insulating
standards and provided with a handle for turning it. One or more
cushions of leather are held on an insulated support, so as to rub
against the plate or cylinder as it is turned. A metal comb or combs are
held on another insulating support so as to be nearly in contact with
the surface of the glass plate at a point as far removed as possible
from the rubbers. The combs are attached to a brass ball or round-ended
cylinder, which is termed the prime conductor.

In use either the prime conductor or cushions are connected by a chain
or otherwise with the earth. Assume it to be the cushions. As the
machine is worked by turning the plate, the glass and cushion being in
contact develop opposite electricities. The glass is charged with
positive electricity, and as it turns carries it off and as it reaches
the prime conductor by induction and conduction robs it of its negative
electricity. Meanwhile the cushions negatively excited deliver their
charge to the earth. The action thus goes on, the prime conductor being
charged with positive electricity.


If the prime conductor is connected to the earth and the cushions are
left insulated, negative electricity can be collected from the cushions.

In some machines both prime conductor and cushions are kept insulated
and without ground contact. Electrodes connecting with each are brought
with their ends close enough to maintain a sparking discharge.

Machine Influence.
A static electric machine working by induction to build up charges of
opposite nature on two separate prime conductors. In general they are
based on the principle of the electrophorous. Work is done by the
operator turning the handle. This rotates a disc and draws excited parts
of it away from their bound charges. This represents a resistance to
mechanical motion. The work absorbed in overcoming this mechanical
resistance appears as electric energy. There are various types of
influence machines, the Holtz, Toeppler-Holtz and Wimshurst being the
most used. The electrophorous, q. v., is a type of influence machine.

Machine, Holtz Influence.
A static electric machine. It includes two plates, one of which is
rapidly rotated in front of the other. Two armatures of paper are
secured to the back of the stationary plate at opposite ends of a
diameter. To start it one of these is charged with electricity. This
charge by induction acts through the two thicknesses of glass upon a
metal bar carrying combs, which lies in front of the further side of the
movable plate. The points opposite the armature repel electrified air,
which strikes the movable disc and charges it. A second rod with comb at
the opposite end of the same diameter acts in the reverse way. Thus
opposite sections of the disc are oppositely charged and the combs with
them. By induction these portions of the disc react upon the two
armatures. The opposite electricities escape from the armatures by paper
tongues which are attached thereto and press against the back of the
movable plate. As the plate rotates the opposite electricities on its
face neutralize the electricity repelled from the combs. The charges on
the back strengthen the charges of the armatures and brass combs. Thus
the machine builds up, and eventually a discharge of sparks takes place
from the poles of the brass combs.


Machine, Toeppler-Holtz.
A modification of the Holtz machine. The priming charge of the armatures
is produced by friction of metallic brushes against metallic buttons on
the face of the rotating plate. (See Machine, Holtz.)

Machine, Wimshurst.
A form of static influence machine. It consists of two plates of glass,
on which radial sectors of tinfoil are pasted. Both plates are rotated
in opposite directions. The sectors of the two plates react one upon the
other, and electric charges of opposite sign accumulate on the opposite
sides of the plates and are collected therefrom by collecting combs.

A name, derived from Maxwell, and suggested for the unit of inductance.
It is due to Oliver Heaviside, but has never been adopted. (See Henry.)

Magne-Crystallic Action.
The action of a supposed force of the same name, proposed by Faraday. It
relates to the different action of a magnetic field upon crystalline
bodies, according to the position of their axes of crystallization. A
needle of tourmaline, normally paramagnetic, if poised with its axis
horizontal, is diamagnetic. Bismuth illustrates the same phenomenon. The
subject is obscure. Faraday thought that he saw in it the action of a
specific force.

A body which tends when suspended by its centre of gravity to lay itself
in a definite direction, and to place a definite line within it, its
magnetic axis, q. v., in a definite direction, which, roughly speaking,
lies north and south. The same bodies have the power of attracting iron
(Daniell), also nickel and cobalt.

Magnets are substances which possess the power of attracting iron.

[Transcriber's note: Edward Purcell and others have explained magnetic
and electromagnetic phenomenon as relativistic effects related to
electrostatic attraction. Magnetism is caused by Lorentz contraction of
space along the direction of a current. Electromagnetic waves are caused
by charge acceleration and the resulting disturbance of the
electrostatic field. (Electricity and Magnetism: Berkeley Physics
Course Volume 2, 1960)]

Magnet, Anomalous.
A magnet possessing more than the normal number (two) of poles. If two
straight magnets are placed end to end with their south poles in
juxtaposition the compound bar will seem to possess three poles, one at
each end and one in the middle. The apparent pole in the middle is
really made up of two consequent poles, q. v. It sometimes happens that
when a single long thin bar is magnetized consequent poles are produced,
although such magnet is in one piece. This may be accidental, as in such
case it is quite hard to avoid anomalous poles, or, as in the field
magnets of some forms of dynamos, anomalous poles may be purposely

Magnet, Artificial.
A magnet formed artificially by any method of magnetization (see
Magnetism) applicable to permanent magnets, electro-magnets and
solenoids. It expresses the distinction from the natural magnets or
lodestone, q. v. It is made of steel in practice magnetized by some of
the methods described under Magnetization.


Magnet, Axial.
A straight-solenoid with axial core.

Magnet, Bar.
A bar magnet is one in the shape of a bar, i. c., straight with parallel
sides and considerably longer than wide or deep.

Magnet, Bell-shaped.
A form of permanent magnet used in some galvanometers. In shape it is a
thick-sided cylindrical box with two slots cut out of opposite sides, so
as to make it represent a horseshoe magnet. Its shape enables it to be
surrounded closely by a mass of copper, for damping its motion, to
render the instrument dead-beat. Such a magnet is used in Siemens &
Halske's galvanometer.

Magnet Coil.
A coil to be thrust over an iron core, to make an electro-magnet. They
are often wound upon paper or wooden bobbins or spools, so as to be
removable from the core if desired.

Magnet, Compensating.
(a) A magnet fastened near a compass on an iron or steel ship to
compensate the action of the metal of the ship upon the magnetic needle.
The ship itself always has some polarity and this is neutralized by one
or more compensating magnets.

(b) See below.

Magnet, Controlling.
A magnet attached to a galvanometer by which the directive tendency of
its magnetic needle is adjusted. In the reflecting galvanometer it often
is a slightly curved magnet carried by a vertical brass spindle rising
from the center of the instrument, and which magnet may be slid up and
down on the spindle to regulate or adjust its action.

Synonym--Compensating Magnet.

Magnet, Compound.
A permanent magnet, built up of a number of magnets. Small bars can be
more strongly magnetized than large. Hence a compound magnet may be made
more powerful than a simple one.

Magnet Core.
The iron bar or other mass of iron around which insulated wire is wound
for the production of an electro-magnet. The shapes vary greatly,
especially for field magnets of dynamos and motors. For these they are
usually made of cast iron, although wrought iron is preferable from the
point of view of permeability.

Magnet, Damping.
A damping magnet is one used for bringing an oscillating body to rest.
The body may be a metallic disc or needle, and the action of the magnet
depends on its lines of force which it establishes, so that the body has
to cut them, and hence has its motion resisted.


Magnet, Deflection of.
The change of position of a magnet from the plane of the earth's
meridian in which it normally is at rest into another position at some
angle thereto, by the effect of an artificial magnetic field, as the
deflection of a galvanometer needle.

Magnet, Electro-.
A magnet consisting of a bar of iron, bundle of iron wires, iron tube or
some equivalent, around which a coil of insulated wire is wound. Such
combination becomes polarized when a current is passed through it and is
an active magnet. On the cessation of the current its magnetism in part
or almost completely disappears. (See Electro-magnet.)

Magnet, Equator of.
In a magnet the locus of points of no attractive power and of no
polarity. In a symmetrical, evenly polarized magnet it is the imaginary
line girdling the centre. The terms Neutral Point or Neutral Line have
displaced it.

Synonyms--Neutral Line--Neutral Point.

Magnet, Field.
A magnet, generally an electro-magnet, used to produce the field in a
dynamo or motor.

Magnet, Haarlem.
Celebrated magnets made in Haarlem, Holland. Logeman, Van Wetteren,
Funckler and Van der Willigen were the makers who gave the celebrity to
the magnets. They were generally horseshoe magnets, and would carry
about twenty times their own weight.

Magnet, Horseshoe.
A magnet of U shape--properly one with the poles brought a little closer
together than the rest of the limbs. For direct lifting and attractive
effects it is the most generally adopted type. Its advantage as regards
lifting effect is due to small reluctance, q. v., offered by a complete
iron circuit, such as the armature and magnet together produce. As the
term is now used it is applied to any U shaped magnet.


Magnet, Joule's Electro.
An electro-magnet of the shape of a cylinder with a longitudinal segment
cut-off. It is wound with wire as shown. The segment cut-off is a piece
of the same shape as the armature. It is of high power.


Magnetic Adherence.
The tendency of a mass of iron to adhere to the poles of a magnet. It is
best figured as due to the virtual shortening of lines of force, as the
more permeable iron gives a better path for them than the air can
afford, and consequently a virtually shorter one.

Magnetic Attraction and Repulsion.
The attraction of a magnet for iron, steel, nickel and cobalt and of
unlike poles of magnets for each other. It is identical with
electro-magnetic attraction, q.v. (Also see Electro-magnetism.)

Magnetic Attraction and Repulsion, Coulomb's Law of.
Magnetic attraction and repulsion are inversely as the square of the
distance. (Ganot.)

While theoretically true in the case of isolated poles, in practise it
does not generally apply on account of the large diameter and relative
shortness of magnets.

Magnetic Axis.
The line connecting the poles of a magnet. It does not generally
coincide exactly with any symmetrical axis of figure. In such cases an
error is introduced into the indications of the needle which must be
determined and allowed for in compasses. To determine it with a magnetic
needle the suspension cup is made removable, so that the needle can be
reversed. Readings are taken with one side of the needle and then with
the other side of the needle up, and the average corresponds with the
position of the magnetic axis in both positions of the needle.

Magnetic Azimuth.
The angle, measured on a horizontal circle, between the magnetic
meridian and a great circle of the earth passing through the observer
and any observed body. It is the astronomical azimuth of a body referred
to the magnetic meridian and therefore subject to the variation of the
compass. The angle is the magnetic azimuth of the observed body.

Magnetic Battery.
A name for a compound permanent magnet; one made up by bolting or
clamping together, or to single soft iron pole pieces, a number of
single permanent magnets. There are a number of forms of compound
magnets. In making them care has to be taken to have them of even
strength. It is also well to have them slightly separated. The object of
both these precautions is to prevent a stronger element or magnet from
depolarizing its neighbor.

Synonym--Compound Magnet.

Magnetic Bridge.
An apparatus for testing the relative permeability of iron. It consists
of a rectangular system of iron cores. Three of the sides are wound with
wire as shown. The other side is built up of double bars, and from the
centre two curved arms rise, as shown in the cut. The arms do not touch.
Between them a short magnet is suspended by a filament, which also
carries a mirror and an index.



A lamp and scale are provided as in the reflecting galvanometer. When
adjusted the magnetic needle hangs as shown in the cut, Fig. 219,
without any tendency to turn towards either curved pole piece. If all
iron parts are symmetrical and of similar metal, a current through the
coils will make no difference. It will work in magnetic opposition upon
the two arms, or, in other words, will maintain both arms at identical


If there is the least difference in permeability, length or thickness
between any of the iron bars the magnetic potential of the two curved
arms will differ, and the magnetic needle will turn one way or the
other. In practical use different samples of iron are substituted for
the unwound members of the fourth side of the parallelogram, and the
needle by its motions indicates the permeability.

In the cut, Fig. 220, D D are the ends of the curved pole pieces; A the
wire carrying the mirror B and magnetic needle N, and E is the index
which shows the larger deflections.


Magnetic Circuit.
A magnetic field of force is characterized by the presence of lines of
force, which, while approximately parallel, curve around and tend to
form closed curves. The polarity of a field of force is referred to an
imaginary direction of the lines of force from the north pole through
space to the south pole, and in the part of the field corresponding to
the body of the magnet, from the south to the north pole. The cut
indicates these features. Hence the magnetic field of force is termed
the magnetic circuit, and to it are attributed a species of resistance
termed reluctance, q. v., and the producing cause of the field or lines
of force is termed sometimes magneto-motive force, q. v.) corresponding
to the electro-motive force. The modern treatment of the magnetic
circuit is similar to the application of Ohm's law and the laws of
resistance and conductivity to the electric circuit.

Magnetic Circuit, Double.
A magnetic circuit which virtually represents two horseshoe magnets
placed with their like poles in contact. It is used for field magnets,
the armatures occupying a place between the consequent poles.


Magnetic Concentration of Ores.
The concentration of ores or the freeing them from their gangue by
magnetic attraction. It is only applicable to those cases in which
either the ore itself or the gangue is attracted by the magnet. Its
principal application is to the concentration of magnetic iron sands.
(See Magnetic Concentration.)

Magnetic Concentrator.
An apparatus similar to a magnetic separator, q. v., but used to
concentrate magnetic iron sands. By the action of electro-magnets the
magnetic iron sand (magnetite) is separated from the sand with which it
is mixed.

Magnetic Conductivity and Conductance.
The first notion of permeance and of the magnetic circuit included the
idea of magnetic conductivity, which conducted lines of force urged by
magneto-motive force through a magnetic circuit. The terms are displaced
by permeability and permeance.


Magnetic Continuity.
The completeness of a magnetic circuit, as when the armature of a
horseshoe magnet is in contact with both poles. It is an attribute of a
paramagnetic substance only and is identical for permanent magnets or
for electro-magnets. An air space intervening between armature and
magnet poles, or a space filled with any diamagnetic substance prevents
continuity, although the lines of force to some extent still find their
way around. The leakage is increased by discontinuity.

Magnetic Control.
Control of a magnetic needle, magnet, iron index or armature, in a
galvanometer, ammeter or voltmeter by a magnetic field; the restitutive
force being derived from a permanent magnet.

Magnetic Couple.
The couple of magnetic force which tends to bring the magnetic needle
into the plane of the magnetic meridian. One force is represented by the
imaginary pull upon the north pole, and the other by the opposite pull
upon the south pole of the needle. The moment of the couple varies from
a maximum when the needle is at right angles to the plane of the
magnetic meridian to zero when it is in such plane.

Magnetic Creeping.
Viscous hysteresis; the slow increase of magnetism in a paramagnetic
body when exposed to induction.


Magnetic Curves.
The pictorial representation of magnetic lines of force. It is generally
produced by scattering filings on a sheet of paper or pane of glass held
over a magnet. The filings arrange themselves in characteristic curves.
Tapping the paper or pane of glass facilitates the arrangement, or
jarring the filings off a smaller magnet, so that they fall polarized
upon the paper, is thought by some to improve the effect. The group of
curves forms what are termed magnetic figures, q. v.


Magnetic Declination.
The angular deviation of the magnetic needle, causing it to rest at an
angle with the true meridian; the variation of the compass. (See
Magnetic Elements.)

Magnetic Density.
The intensity of magnetization expressed in lines of force per stated
area of cross-section in a plane at right angles to the lines of force.

Magnetic Dip.
The inclination from the horizontal assumed by a magnetic needle free to
move in the vertical plane. (See Magnetic Elements.) The angle of dip or
inclination is entirely a function of the earth, not of the needle.

Magnetic Discontinuity.
A break or gap in a magnetic circuit. To make a complete circuit the
iron or other core must be continuous. If the armature of a horseshoe
magnet is in contact with both poles the continuity is complete. If the
armature is not in contact magnetic continuity gives place to
discontinuity. It is an attribute of a paramagnetic substance only, and
is identical for permanent magnets, or for electro-magnets.

Magnetic Elements.
The qualities of the terrestrial magnetism at any place as expressed in
its action upon the magnetic needle. Three data are involved.

I. The Declination or Variation.
II. The Inclination or Dip.
III. The Force or Intensity.

I. The Declination is the variation expressed in angular degrees of the
magnetic needle from the true north and south, or is the angle which the
plane of the magnetic meridian makes with that of the geographical
meridian. It is expressed as east or west variation according to the
position of the north pole; east when the north pole of the needle is to
the east of the true meridian, and vice versa. Declination is different
for different places; it is at present west in Europe and Africa, and
east in Asia and the greater part of North and South America. The
declination is subject to (a) secular, (b) annual and (c) diurnal
variations. These are classed as regular; others due to magnetic storms
are transitory and are classed as irregular, (a) Secular variations. The
following table shows the secular variations during some three hundred
years at Paris. These changes are termed secular, because they require
centuries for their completion.


Table of Declination or Variation at Paris.
Year.   Declination.
1580   11º 30' E.
1663    0°
1700    8° 10' W.
1780   19º 55' W.
1785   22º 00' W.
1805   22º  5' W.
1814   22º 34' W.
1825   22° 22' W.
1830   22º 12' W.
1835   22º  4' W.
1850   20º 30' W.
1855   19º 57' W.
1860   19º 32' W.
1865   18º 44' W.
1875   17º 21' W.
1878   17º 00' W.
[Transcriber's note The value for 2008 is about  0° 48' W, changing by
0° 7' E/year.]

On scrutinizing these figures it will be seen that there is part of a
cycle represented and that the declination is slowly returning to the
zero point after having reached its maximum western variation in 1814.
Upwards of 300 years would be required for its completion on the basis
of what is known. In other places, notably the coast of Newfoundland,
the Gulf of the St. Lawrence and the rest of the North American seaboard
and in the British Channel, the secular variations are much more rapid
in progress. (b) Annual variations--These were first discovered in 1780
by Cassini. They represent a cycle of annual change of small extent,
from 15' to 18' only. In Paris and London the annual variation is
greatest about the vernal equinox, or March 21st, and diminishes for the
next three months, and slowly increases again during the nine following
months. It varies during different epochs. (c) Diurnal variations were
discovered in 1722 by Graham. A long needle has to be employed, or the
reflection of a ray of light, as in the reflecting galvanometer, has to
be used to observe them. In England the north pole of the magnetic
needle moves every day from east to west from sunrise until 1 or 2 P.
M.; it then tends towards the east and recovers its original position by
10 P. M. During the night the needle is almost stationary. As regards
range the mean amplitude of diurnal variations at Paris is from April to
September 13' to 15'; for the other months from 8' to 10'. On some days
it amounts to 25' and sometimes is no more than 5'. The amplitude of
diurnal variations decreases from the poles to the equator. Irregular
variations accompany earthquakes, the aurora borealis and volcanic
eruptions. In Polar regions the auroral variations may be very great;
even at 40° latitude they may be 1° or 2°. Simultaneous irregularities
sometimes extend over large areas. Such are attributed to magnetic
storms. II. The Inclination is the angle which the magnetic needle makes
with the horizon, when the vertical plane in which the needle is assumed
to be free to move coincides with the magnetic meridian. It is sometimes
called the dip of the needle. It varies as does the declination, as
shown in the following table of inclinations of London.


Table of Inclination or Dip at London
Year.   Inclination.
1576   71° 50'
1600   72°
1676   73° 30'
1723   74° 42'
1773   72° 19'
1780   72°  8'
1790   71° 33'
1800   70° 35'
1821   70° 31'
1828   69° 47'
1838   69° 17'
1854   68° 31'
1859   68° 21'
1874   67° 43'
1876   67° 39'
1878   67° 36'
1880   67° 35'
1881   67° 35'

III. Force or Intensity is the directive force of the earth. It varies
with the squares of the number of oscillations the magnetic needle will
make if caused to oscillate from a determined initial range. The
intensity is supposed to be subject to secular change. According to
Gauss the total magnetic intensity of the earth is equal to that which
would be exerted if in each cubic yard there were eight bar magnets,
each weighing one pound. This is, of course, a rough way of expressing
the degree of intensity. Intensity is least near the magnetic equator
and greatest near the magnetic poles; the places of maximum intensity
are termed the magnetic foci. It varies with the time of day and
possibly with changes in altitude.

Magnetic Elongation.
The elongation a bar of iron or steel undergoes when magnetized. By
magnetization it becomes a little longer and thinner, there being no
perceptible change in volume. The change is accompanied by a slight
sound--the magnetic tick. An exceedingly delicate adjustment of
apparatus is required for its observation.

Magnetic Equator.
A locus of the earth's surface where the magnet has no tendency to dip.
It is, approximately speaking, a line equally distant from the magnetic
poles, and is called also the aclinic line. It is not a great circle of
the earth.


Magnetic Field of Force.
The field of force established by a magnet pole. The attractions and
repulsions exercised by such a field follow the course of the electro-
magnetic lines of force. (See also Field of Force.) Thus the tendency of
a polarized needle attracted or repelled is to follow, always keeping
tangential to curved lines, the direction of the lines of force, however
sweeping they may be. The direction of magnetic lines of force is
assumed to be the direction in which a positive pole is repelled or a
negative one attracted; in other words, from the north pole of a magnet
to its south pole in the outer circuit. The direction of lines of force
at any point, and the intensity or strength of the field at that point,
express the conditions there. The intensity may bc expressed in terms of
that which a unit pole at unit distance would produce. This intensity as
unitary it has been proposed to term a Gauss. (See Weber.)

The direction of the lines of force in a magnetic field are shown by the
time-honored experiment of sprinkling filings of iron upon a sheet of
paper held over a magnet pole or poles. They arrange themselves, if the
paper is tapped, in more or less curved lines tending to reach from one
pole of the magnet to the other. Many figures may be produced by
different conditions. Two near poles of like name produce lines of force
which repel each other. (See Magnetic Curves.)

A magnetic and an electro-magnetic field are identical in all essential
respects; the magnetic field may be regarded as a special form of the
electro-magnetic field, but only special as regards its production and
its defined north and south polar regions.

Synonyms--Magnetic Spin (not much used).

Magnetic Field, Uniform.
A field of identical strength in all parts, such as the earth's magnetic
field. If artificially produced, which can only be approximately done,
it implies large cross-section of magnet pole in proportion to the
length of the magnetic needle affected by it, which is used in
determining its uniformity.

Magnetic Figures.
The figures produced by iron filings upon paper or glass held near
magnetic poles. By these figures the direction of lines of force is
approximately given, and a species of map of the field is shown. (See
Magnetic Field of Force--Magnetic Curves.)

Magnetic Filament.
The successive rows of polarized molecules assumed to exist in
magnetized iron. Each molecule represents an infinitely small magnet,
and its north pole points to the south pole of the next molecule. Such a
string or row is a theoretical conception based on the idea that the
molecules in a magnet are all swung in to parallelism in the magnetizing
process. A magnetic filament may be termed the longitudinal element of a
magnet. (See Magnetism, Hughes' Theory of.)

[Transcriber's note: This description parallels the modern
notion of electron spin as the basis of magnetism in materials.]

Magnetic Fluids.
A two-fluid theory of magnetism has been evolved, analogous to the
two-fluid theory of electricity. It assumes north fluid or "red
magnetism" and a south fluid or "blue magnetism." Each magnetism is
supposed to predominate at its own pole and to attract its opposite.
Before magnetization the fluids are supposed to neutralize each other
about each molecule; magnetization is assumed to separate them,
accumulating quantities of them at the poles.

Magnetic Flux.
Magnetic induction; the number of lines of force that pass through a
magnetic circuit.

Synonym--Magnetic Flow.


Magnetic Force.
The forces of attraction and repulsion exercised by a magnet. By
Ampere's theory it is identical with the forces of attraction and
repulsion of electric currents.

Magnetic Friction.
The damping effect produced on the movements of a mass of metal by
proximity to a magnet; the phenomenon illustrated in Arago's wheel, q.
v. When a mass of metal moves in the vicinity of a magnet it cuts the
lines of force emanating from its poles, thereby producing currents in
its mass; as the production of these currents absorbs energy a damping
effect is produced upon the movements of the mass.

Magnetic Gear.
Friction gear in which electro-magnetic adherence is employed to draw
the wheels together. (See Adherence, Electro-magnetic--Electro-magnetic
Friction Gear.)

Magnetic Inclination.
The inclination from the horizontal of a magnetic needle placed in the
magnetic meridian. (See Magnetic Element--Inclination Map.)

Synonym--Magnetic Dip.

Magnetic Induction.
The force of magnetization within an induced magnet. It is in part due
to the action of the surrounding particles of polarized material; in
part to the magnetic field. (See Magnetic Induction, Coefficient of.)

In a more general way it is the action of a magnet upon bodies in its
field of force. In some cases the magnetism induced causes the north
pole of the induced magnet to place itself as far as possible from the
north pole of the inducing magnet and the same for the south poles. Such
substances are called paramagnetic or ferromagnetic. They lie parallel
or tangential to the lines of force. In other cases the bodies lie at
right angles or normal to the lines of force. Such bodies are called

Some bodies are crystalline or not homogeneous in structure, and in them
the lines of magnetic induction may take irregular or eccentric paths.
(See AEolotropic.)

Synonym--Magnetic Influence.

Magnetic Induction, Apparent Coefficient of.
The apparent permeability of a paramagnetic body as affected by the
presence of Foucault currents in the material itself. These currents act
exactly as do the currents in the coils surrounding the cores of
electro-magnets. They produce lines of force which may exhaust the
permeability of the iron, or may, if in an opposite direction, add to
its apparent permeability.

Magnetic Induction, Coefficient of.
The number, obtained by dividing the magnetization of a body, expressed
in lines of force produced in it, by the magnetizing force which has
produced such magnetization, expressed in lines of force producible by
the force in question in air. It always exceeds unity for iron, nickel
and cobalt. It is also obtained by multiplying the coefficient of
induced magnetization by 4 PI (4 * 3.14159) and adding 1. (See Magnetic
Susceptibility--Magnetization, Coefficient of Induced.)


The coefficient of magnetic induction varies with the material of the
induced mass, and varies with the intensity of the magnetizing force.
This variation is due to the fact that as the induced magnetism in a
body increases, the magnetizing force required to maintain such
induction, increases in a more rapid ratio. The coefficient of magnetic
induction is the same as magnetic permeability, and in a certain sense
is the analogue of conductivity. It is also termed the multiplying power
of the body or core magnetized. It is the coefficient of induced
magnetization (see Magnetization, Coefficient of Induced) referred to a
mass of matter. For diamagnetic bodies the coefficient has a negative
sign; for paramagnetic bodies it has a positive sign.

Synonyms--Permeability--Multiplying Power--Magnetic Inductive Capacity.

Magnetic Induction, Dynamic.
The induction produced by a magnetic field which moves with respect to a
body, or where the body if moving moves at a different rate, or where
the body moves and the field is stationary. In the case where both move,
part of the induction may be dynamic and part static. (See Magnetic
Induction, Static.)

Magnetic Induction, Static.
Magnetic induction produced by a stationary field acting upon a
stationary body.

Magnetic Induction, Tube of.
An approximate cylinder or frustrum of a cone whose sides are formed of
lines of magnetic induction. (See Magnetic Induction, Lines of.) The
term tube is very curiously applied in this case, because the element or
portion of a magnetic field thus designated is in no sense hollow or

Magnetic Inertia.
A sensible time is required to magnetize iron, or for it to part with
its magnetism, however soft it may be. This is due to its magnetic
inertia and is termed the lag. Permanent or residual magnetism is a
phase of it. It is analogous to self-induction of an electric circuit,
or to the residual capacity of a dielectric.

Magnetic Insulation.
Only approximate insulation of magnetism is possible. There is no
perfect insulator. The best ones are only 10,000 times less permeable
than iron. Hence lines of force find their way through air and all other
substance, being simply crowded together more in paths of iron or other
paramagnetic substance.


Magnetic Intensity.
The intensity of the magnetization of a body. It is measured by the
magnetic lines of force passing through a unit area of the body, such
area being at right angles to the direction of the lines of force.

Magnetic Lag.
In magnetism the tendency of hard iron or steel especially to take up
magnetism slowly, and to part with it slowly. (See Magnetic Inertia.)
The lag affects the action of a dynamo, and is a minor cause of those
necessitating the lead of the brushes.

Synonym--Magnetic Retardation.

Magnetic Latitude.
Latitude referred to the magnetic equator and isoclinic lines.

Magnetic Leakage.
The lines of force in a field magnet which pass through the air and not
through the armature are useless and represent a waste of field. Such
lines constitute magnetic leakage.

Magnetic Limit.
The temperature beyond which a paramagnetic metal cannot be magnetized.
The magnetic limit of iron is from a red to a white heat; of cobalt, far
beyond a white heat; of chromium, below a red heat; of nickel at about
350° C. (662°F.) of manganese, from 15° C. to 20° C. (59° to 68° F.)

Magnetic Lines of Force.
Lines of force indicating the distribution of magnetic force, which is
due presumably to whirls of the ether. A wire or conductor through which
a current is passing is surrounded by an electro-magnetic field of
force, q. v., whose lines of force form circles surrounding the
conductor in question. A magnet marks the existence of a similar
electro-magnetic field of force whose lines form circuits comprising
part of and in some places all of the body of the magnet, and which are
completed through the air or any surrounding paramagnetic or diamagnetic
body. They may be thought of as formed by the Ampérian sheet of current,
and analogous to those just mentioned as surrounding a conductor.


A magnetic line of force may be thought of as a set of vortices or
whirls, parallel to each other, and strung along the line of force which
is the locus of their centres.

If as many lines are drawn per square centimeter as there are dynes (per
unit pole) of force at the point in question, each such line will be a
unitary c. g. s. line of force.


Magnetic Mass.
A term for a quantity of magnetism. Unit mass is the quantity which at
unit distance exercises unit force.

Magnetic Matter.
Imaginary matter assumed as a cause of magnetism. Two kinds, one
positive and one negative, may be assumed as in the two fluid theory of
electricity, or only one kind, as in the single fluid theory of
electricity. Various theories of magnetic matter have been presented
whose value is only in their convenience.

[Transcriber's note: See "magnet" and Edward Purcell's explanation of
magnetism using general relativity.]

Magnetic Memory.
The property of retaining magnetism; coercive force; magnetic inertia;
residual magnetism.

[Transcriber's note: Small ferrite magnetic donuts were used as computer
main memory from 1950 to 1970.]

Magnetic Meridian.
A line formed on the earth's surface by the intersection therewith of a
plane passing through the magnetic axis. It is a line determined by the
direction of the compass needle. The meridians constantly change in
direction and correspond in a general way to the geographical meridians.

Magnetic Moment.
The statical couple with which a magnet would be acted on by a uniform
magnetic field of unit intensity if placed with its magnetic axis at
right angles to the lines of force of the field. (Emtage.) A uniformly
and longitudinally magnetized bar has a magnetic moment equal to the
product of its length by the strength of its positive pole.

Magnetic Needle.
A magnet with a cup or small depression at its centre and poised upon a
sharp pin so as to be free to rotate or oscillate in a horizontal plane.
The cup is often made of agate. Left free to take any position, it
places its magnetic axis in the magnetic meridian.

Magnetic Parallels.
Lines roughly parallel to the magnetic equator on all parts of each of
which the dip of the magnetic needle is the same; also called Isoclinic
Lines. These lines mark the places of the intersection of equipotential
surfaces with the earth's surface. They are not true circles, and near
the poles are irregular ellipses; the magnet there points toward their
centres of curvature. They correspond in a general way with the
Geographical Parallels of Latitude.

Magnetic Permeability.
The specific susceptibility of any substance, existing in a mass, for
magnetic induction. (See Magnetic Induction, Coefficient of, synonym for
Magnetic Permeability and Magnetization, Coefficient of Induced.)

Synonyms--Magnetic Inductive Capacity--Multiplying Power--Coefficient of
Magnetic Induction.


Magnetic Perturbations.
Irregular disturbances of the terrestrial magnetism, as by the aurora
and in electric storms.

Magnetic Poles.
The points where the equipotential surfaces of the terrestrial field of
force graze the earth's surface; the points toward which the north or
south poles of the magnetic needle is attracted. Over a magnetic pole
the magnetic needle tends to stand in a vertical position. There are two
poles, Arctic or negative, and Antarctic or positive. Magnetic needles
surrounding them do not necessarily point toward them, as they point to
the centres of curvature of their respective magnetic parallels. The
poles constantly change in position. The line joining them does not
coincide with anything which may be termed the magnetic axis of the

Magnetic Poles, False.
Poles on the earth's surface other than the two regular magnetic poles.
There seem by observation to be several such poles, while analogy would
limit true magnetic poles to two in number.

Magnetic Potential.
The potential at any point of a magnetic field is the work which would
be done by the magnetic forces of the field upon a positive unit of
magnetism as it moves from that point to an infinite distance. (Emtage.)

Magnetic Proof Piece.
A piece of iron used for testing magnets and the distribution of
magnetism in bars, by suspending or supporting above or near the magnet,
by detaching after adherence, and in other ways.

Magnetic Proof Plane.
An exploring coil used for testing the distribution of magnetism. It is
connected in circuit with a galvanometer, and exposed to alternation of
current, or to other disturbing action produced by the magnet or field
under examination. This affects the galvanometer, and from its movements
the current produced in the coil, and thence the magnetic induction to
which it was exposed, are calculated.

Synonym--Exploring Coil.

Magnetic Quantity.
The magnetism possessed by a body; it is proportional to the action of
similar poles upon each other, or to the field produced by the pole in
question. It is also called the strength of a pole.

The force exercised by two similar poles upon each other varies with
their product and inversely with the square of the distance separating
them; or it may be expressed thus (m * m) / (L^2). This is a force, and
the dimensions of a force are ML/(T^2). Therefore, (m^2)/(L^2) =
ML/(T^2) or m = (M^.5)*(L^1.5)/T.


Magnetic Reluctance.
The reciprocal of permeance; magnetic resistance; the relative
resistance to the passage of lines of force offered by different
substances. The idea is derived from treating the magnetic circuit like
an electric one, and basing its action on magneto-motive force acting
through a circuit possessing magnetic reluctance.

Magnetic Reluctivity.
The reciprocal of magnetic permeability, q. v.

Synonym--Magnetic Resistance.

Magnetic Retentivity.
The property of steel or hard iron by which it slowly takes up and
slowly parts with a magnetic condition--traditionally (Daniell) called
coercitive force.

Magnetic Rotary Polarization.
If a plane polarized beam of light is sent through a transparent medium
in a magnetic field its plane of polarization is rotated, and this
phenomenon is denoted as above. (Compare Refraction, Electric, and see
Electro-magnetic Stress.) This has been made the basis of a method for
measuring current. A field of force varies with the current; the
polarization produced by such field is therefore proportional to the
current. (Becquerel & Rayleigh.)

A plane polarized beam of light passing through the transparent medium
in the magnetic field by the retardation or acceleration of one of its
circular components has its plane of polarization rotated as described.
The direction of the lines of force and the nature of the medium
determine the sense of the rotation; the amount depends upon the
intensity of the field resolved in the direction of the ray, and on the
thickness and nature of the medium.

Magnetic Saturation.
The maximum magnetic force which can be permanently imparted to a steel
bar. A bar may be magnetized beyond this point, but soon sinks to it.
The magnetism produced in a bar is prevented from depolarization by the
retentivity or coercive force of the bar. The higher the degree of
magnetization the greater the tendency to depolarization.

It is also defined as the maximum intensity of magnetism produced in a
paramagnetic substance by a magnetic field as far as affected by the
permeability of the substance in question. The more lines of force
passed through such a substance the lower is its residual permeability.
It is assumed that this becomes zero after a certain point, and then the
point of saturation is reached. After this point is reached the addition
of any lines of force is referred entirely to the field and not at all
to the permeability of the substance. But such a zero is only definable

Magnetic Screen.
A box or case of soft iron, as thick as practicable, for protecting
bodies within it from the action of a magnetic field. The lines of force
to a great extent keep within the metal of the box on account of its
permeability, and but a comparatively few of them cross the space within

Such screens are used to prevent watches from being magnetized, and are
a part of Sir William Thomson's Marine galvanometer.

A magnetic screen may be a sphere, an infinite or very large plane, or
of the shape of any equipotential surface.

Synonym--Magnetic Shield.


Magnetic Self-induction.
The cause of a magnet weakening is on account of this quality, which is
due to the direction of the lines of force within a magnet from the
positive towards the negative pole. "A magnet thus tends to repel its
own magnetism and to weaken itself by self-induction." (Daniell.)

Magnetic Separator.
An apparatus for separating magnetic substances from mixtures. Such
separators depend on the action of electro-magnets. In one form the
material falls upon an iron drum, magnetized by coils. Any magnetic
substance adheres to the drum and is thereby separated. They are used by
porcelain makers for withdrawing iron particles from clay, by machinists
to separate iron filings and chips from brass, and for similar purposes.


Magnetic Shell.
A theoretical conception of a cause of a magnetic field or of a
distribution of magnetism. If we imagine a quantity of very short
magnets arranged in contact with their like poles all pointing in the
same direction so as to make a metal sheet, we have a magnetic shell.
Its magnetic moment is equal to the sum of the magnetic moment of all
its parts. If the shell is of uniform strength the magnetic moment of a
unit area gives the strength of the shell; it is equal to the magnetic
quantity per unit of area, multiplied by the thickness of the shell.

If its strength is uniform throughout a magnetic shell is called simple;
if its strength varies it is termed complex.

Emtage thus defines it: A magnetic shell is an indefinitely thin sheet
magnetized everywhere in the direction normal to itself.

Magnetic Shell, Strength of.
The magnetic quantity per unit of area of the shell multiplied by the
thickness of the shell.


Magnetic Shield.
In general a magnetic screen, q. v. Sometimes a strong local field is
made to act as a shield, by its predominance overcoming any local or
terrestrial field to which the needle to be protected may be exposed.

Magnetic Shunt.
The conception of a magnetic circuit being formed, the shunt is a
corollary of the theory. It is any piece of iron which connects points
of a magnet differing in polarity, so as to divert part of the lines of
force from the armature or yoke. The shunt is especially applicable in
the case of horseshoe magnets. Thus a bar of iron placed across from
limb to limb a short distance back from the poles would act as a shunt
to the armature and would divert to itself part of the lines of force
which would otherwise go through the armature and would weaken the
attraction of the magnet for the latter. In dynamos a bar of iron used
as a magnetic shunt has been used to diminish the lines of force going
through the armature and hence to weaken the field and diminish the
electro-motive force. By moving the shunt nearer or further from the
poles the dynamo is regulated.

In the cut the projections between the yoke and poles of the magnet
shown act as a shunt to the yoke, taking some lines of force therefrom.


Magnetic Storms.
Terrestrial magnetic disturbances sometimes covering very wide areas,
and affecting the magnetic declination and inclination. One such
disturbance was felt simultaneously at Toronto, Canada, the Cape of Good
Hope, Prague and Van Diemen's Land. (Sabine.)


Magnetic Strain.
The strain produced by magnetic lines of force in substances exposed to
their action. It is observed in substances placed between the poles of a
strong electro-magnet, and evinces itself in the alteration of the
optical properties of transparent substances.

Magnetic Stress.
The stress produced by magnetic lines of force on substances through
which they pass, evidenced in alteration of the optical properties of
transparent bodies thus treated.

Magnetic Susceptibility.
The specific intrinsic susceptibility of any material for magnetic
induction. It refers to the particle of matter, and not to the mass, as
in the latter its own particles react on each other and bring about what
is termed permeability, q. v. (See also Magnetization, Coefficient of
Induced, and Magnetic Induction, Coefficient of.)

Synonym--Coefficient of Induced Magnetization.

Magnetic Tick.
When a bar of iron is suddenly magnetized or demagnetized it emits a
slight sound, called the Page sound, or the magnetic tick. This has been
utilized in a telephone by Reiss. The telephone will receive sound, but
is very weak. It consists of a bar surrounded with a coil of insulated
wire. Variations in current produce sounds, which may be articulate if
the currents are produced by a telephonic transmitter.

Magnetic Twist.
A bar of iron held in the magnetic meridian and pointing to the pole and
twisted becomes to some extent permanently magnetized. Conversely a bar
when magnetized seems to have a twist set up in it. The latter is
magnetic twist.

Magnetic Variations.
Changes in the value of magnetic declination or inclination. (See
Magnetic Elements.)

Magnetism, Ampére's Theory of.
A theory accounting for magnetic phenomena by assuming the existence of
currents circulating around the molecules of permanent magnets. If such
currents so circulate and all in the same direction, the result is the
same as if the body of the magnet was enveloped in currents representing
those of an electro-magnet or solenoid. This is because in the interior
the current around one molecule would counteract the current around its
neighboring ones in part, so that the only virtual currents left would
be represented by those on the outer surfaces of the outer shell of
molecules, and these virtually resolve themselves into one general
current sheet, surrounding the magnet and coinciding with its surface.

The theory assumes that such currents permanently circulate around the
molecules of paramagnetic substances. Under ordinary conditions there is
no coincidence in their direction and no resultant current is produced.
When magnetized or polarized the molecules are brought into order, so
that the direction of their current coincides and the body becomes a



At the north pole of the magnet the direction of the Ampérian currents
is the reverse of that of a watch when the observer faces the pole; the
reverse obtains for the south pole.

The attraction of opposite and repulsion of similar poles is explained
by the actions of the Ampérian currents upon each other. If north and
south pole are placed together these currents will coincide in direction
and hence will attract each other. If two like poles are put together
the currents will have opposite directions and will repel each other.

No energy is supposed to be required to maintain currents around or in a
single molecule.


Magnetism, Blue.
A term arising from the two fluid theory of magnetism; the magnetism of
the south pole of a magnet. (See Magnetic Fluids.) The magnetism of the
north pole is termed red magnetism. Both terms originated presumably in
the painting of magnets, and are little used.

Synonym--South Magnetic Fluid.


Magnetism, Components of Earth's.
The magnetic force of the earth acts in the plane of the magnetic
meridian and in direction generally lies oblique to the plane of the
horizon. It can be resolved into two components, one vertical, which has
no directive effect upon the magnetic needle, the other horizontal,
which represents the directive element for the usual compass needle. For
the dipping needle, q. v., the vertical component is the only active
one. A magnetic needle mounted on a universal joint at its centre of
gravity would be acted on by both components.

Magnetism, Creeping of.
The gradual increase of magnetism when a magnetic force is applied with
absolute steadiness to a piece of iron. It is a form of magnetic lag. It
may last for half an hour and involve an increase of several per cent.
of the total magnetism.

Synonym--Viscous Hysteresis.

Magnet, Iron Clad.
A magnet with a casing of iron connected at one end to the core. The
term is generally applied to electromagnets of this form.

Synonyms--Tubular Magnet--Jacketed Magnet.

Magnetism, Decay of.
The gradual loss of magnetism by permanent magnets, due to accidental
shocks, changes of temperature, slow spontaneous annealing of the iron
and other similar causes.

Magnetism, Discharge of.
The loosing of magnetization. Thus in a shunt-wound dynamo there is a
critical resistance for the outer circuit, below which the field ceases
to be magnetized, as enough current ceases to be shunted into it to
magnetize it. The machine is said to unbuild itself, and a discharge of
magnetism occurs from the field magnet.

Magnetism, Ewing's Theory of.
Ewing found by a model consisting of a number of pivoted magnetic
needles that the observed phenomena of magnetization could be
represented thereby. Thus there would be no need of assuming internal
frictional forces of Maxwell, nor the closed rings or chains of Hughes.
The theory retains the notion, however, of paramagnetic matter,
consisting of an assemblage of molecular magnets. The loss of energy by
hysteresis is represented in the model by the energy lost by the needles
in beating against the air.


Magnetism, Free.
The magnetism or magnetic field outside of a magnetic circuit. It is due
to escape of lines of force and to the magnetic leakage through the air.
The lines of force are never, under the most favorable circumstances,
confined to the metallic circuit of the magnet and armature. In a simple
magnet without armature all the lines of force have to follow an air
path, and the field is at its strongest. As the magnetism is strongest
at the surface near the poles, the term is sometimes understood as
applying to the surface attraction. In such case it is defined as the
distribution, on a magnetized bar or mass, of magnetic lines of force as
they emerge from its surface.

Synonym--Surface Magnetization.

Magnetism, Hughes' Theory of.
A theory accounting for magnetic phenomena by assuming that each
molecule is a magnet, and that in a polarized or magnetized body they
are all arranged with their poles in the same direction, while in an
unmagnetized body their poles, alternating in direction, neutralize each

Magnetization consists in a partial rotation of the molecules so as to
make them agree in position, thus, as a resultant developing north and
south poles at the ends of the bar.

The theory is in a certain sense simpler than Ampere's theory, but is
not so generally adopted.

Magnetism, Lamellar Distribution of.
The distribution of magnetism in thin and uniform or "simple magnetic
shells," q. v. A given distribution is termed lamellar if the substance
in which it exists can be divided into simple magnetic shells, which
either form closed surfaces, or have their edges in the surface of the
substance. In lamellar distribution the polar area is very large
compared with the distance between opposite poles.

Magnetism of Gases.
Faraday experimented on this point by coloring gases with a little vapor
of iodine or other colored gas, and letting them flow between the two
poles of a powerful electromagnet. In this way he found some are
repelled, some attracted, and in the case of oxygen, it is attracted at
one temperature and repelled at another. At ordinary temperatures a
cubic yard of oxygen possesses the magnetism of 5.5 grains of iron and
when liquefied it is strongly attracted.

Magnetism or Magnetization, Temporary.
When a mass of iron is magnetized by a current, when the current ceases
the portion of its magnetism which disappears is the temporary
magnetism; the portion retained is the residual or permanent magnetism.

Magnetism, Red.
A term arising from the two fluid theory of magnetism; the magnetism of
the north pole of a magnet. (See Magnetic Fluids.) The magnetism of the
south pole is termed blue magnetism. Both terms originated in the
painting of magnets. They are but little used.

Synonym--North Magnetic Fluid.


Magnetic Remanence.
The residual magnetism left in a bar of steel or other paramagnetic
material after the application of a powerful magnet. It is distinguished
from coercive force, as the latter is the amount of negative magnetizing
or of demagnetizing force required to reduce the remanent magnetism to

Synonym--Remanence--Residual Magnetism.

Magnetism, Solenoidal Distribution of.
The distribution of magnetism in such a way that the poles are very far
apart in proportion to their area. The magnetization of a long thin bar
of steel illustrates solenoidal distribution.

Magnetism Sub-permanent.
The magnetism of a paramagnetic substance which presents a considerable
degree of permanency, but which gradually disappears, leaving the
permanent magnetism present. It is noticeable in iron or steel ships
whose magnetism gradually reduced in quantity, eventually becomes fully

Magnetism, Weber's Theory of.
The molecules of a magnetizable material by this theory are supposed to
be magnets with their poles lying in every direction, and hence
neutralizing each other. By magnetization these are supposed to be
turned with their similar poles in the same direction, and their axis
parallel, hence acting like a group of magnets. It is practically
identical with Hughes' theory.

Magnetism, Terrestrial.
The magnetism of the earth. (See Magnetic Elements.)


Magnetization by Double Touch.
The process of magnetizing a steel bar by simultaneously stroking it
with two poles of a horseshoe magnet or with two opposite poles of two
bar magnets. The poles must be close but not touching. A block of wood
may be placed between the ends if single magnets are used. The poles are
placed on the middle of the bar and carried back and forth to one end,
then to the other, and so on, ending at the middle of the bar in such
direction as to give each end the same number of strokes. The poles must
be close together or consequent poles will be produced. If bar magnets
are used they may be held inclined at an angle of 15º to 20º with the
horizontal bar to be magnetized. The ends of the latter may rest on
poles of two other magnets, each end on a pole of the same name as that
of the magnetizing magnet on its side. (See Magnetization, Hoffer's


Magnetization by Separate Touch.
A method of magnetization. Two magnets are used. Held in an inclined
position two opposite poles are touched to the bar near its centre, and
are drawn off to the two ends. They are returned through the air and the
process is repeated.

Magnetization by Single Touch.
A method of polarizing or magnetizing steel bars, by stroking them
always in one direction with one pole of a magnet, returning it through
the air. The stroking is best done on both sides. The stroking may begin
at one end and end at the other, or it may be commenced in the center of
the bar and be carried to one end with one pole, and the same done for
the other half with the other pole.

Magnetization by the Earth.
The earth imparts magnetism to iron masses. If a rod of steel is held
parallel to the inclination and in the magnetic meridian it exhibits
polarity, which by jarring or hammering, can be made to some extent
permanent. A piece of soft iron held vertically, or still better in the
line of the dip as above, and which is twisted when in that position,
becomes magnetized with some degree of permanence. Many other instances
are cited, such as fire-irons, lamp-posts, iron gates, lathe turnings,
all of which often exhibit polarity, having been magnetized by the
earth's field.

[Transcriber's note: The earth's magnetic field is believed to originate
it electric currents in the moving molten core.]

Magnetization, Coefficient of Induced.
The coefficient (q. v.) expressing the relation between the specific
intensity of magnetization of a particle and the magnetizing force. The
magnetizing force is measured by the lines of force it can produce in a
field of air. The coefficient of induced magnetization is the factor by
which the intensity of a magnetizing field must be multiplied to produce
the magnetization imparted by it to a particle of any substance. This
coefficient varies for different substances, and is also called magnetic
susceptibility. It is distinguished from permeability as referring only
to a particle isolated from influence of a mass of surrounding particles
of its own kind. It is definable as the intensity of the magnetization
assumed by an exceedingly long and exceedingly thin bar placed in a unit
field. If a mass of metal were placed in such a field all its particles
would become affected and within the mass no unit field could exist.
Hence magnetic susceptibility (another name for this coefficient) does
not apply to the case of large cores of electro-magnets and
dynamo-armatures, but is really a theoretical rather than a practical

The sign of the coefficient of diamagnetic bodies is negative; of
paramagnetic bodies is positive.

Synonym--Magnetic Susceptibility.   \


Magnetization, Cycle of.
A cycle of positive or of positive and negative magnetization represents
the application of a magnetizing force beginning at a fixed value,
generally zero, rising to a maximum, or to a value of maximum distance
from the initial and then returning to the original basis. It is
virtually a full wave of magnetization and may extend on both sides of a
zero line giving positive and negative values.

Cycles of magnetization apply especially to transformers and other
apparatus of that character used with the alternating current system.

Magnetization, Hoffer's Method.
For horseshoe bars an armature is placed against the poles of the magnet
bar to be treated. The poles of a strong horseshoe magnet are stroked
over it from poles to bend and returned through the air, or vice versa.
In the first case the poles will be the same as those of the inducing
magnet; in the second case they will be opposite. A maximum effect is
produced in ten strokes. The stroking should be applied to both sides.
An electro-magnet may be used as inducer as shown, but an armature
should be used; in the cut it is omitted.


Magnetization, Intensity of.
The amount of magnetism induced in or present in a body. It is expressed
in Magnetic Lines of Force, q. v., per cross-sectional area.

Magnetization, Isthmus Method of.
A method used by Ewing in a research on the magnetization of iron in
very strong fields. He used samples of iron turned down in the centre to
a narrow neck, and thus concentrated the lines of force greatly.

Magnetization, Elias' Method.
The bar to be magnetized is surrounded by a magnetizing coil, q. v. A
strong current is passed through it, and the coil is moved back and
forth a few times.

Magnetization, Jacobi's Method.
For horseshoe bars. The bar is placed with its poles against those of a
horseshoe magnet. A bar of soft iron, long enough to reach from outside
to outside of the legs, is laid across near the junction and is drawn
along towards the bend of the new bar and away from it. This is repeated
a few times on both sides.


Magnetization, Limit of.
As the induction of magnetizing force increases, magnetization of
paramagnetic metals tends towards a limit, the increase in magnetization
being continually less and less as the metal becomes more highly
magnetized. In diamagnetic substances no limit is discernible.

Synonym--Maximum Magnetization.

Magnetization, Specific.
The magnetic moment per gram of a substance.

A bar of iron connecting the two poles of a permanent magnet. Often the
same bar serves as armature and keeper.

Magnet, Lamination of.
It is advantageous to make magnets of laminated construction, or of thin
plates of steel. The thin metal can be better tempered or hardened than
thick metal. A slight separation of the plates is advantageous from some
points of view. If in actual contact there is some danger that the
weaker members will have their polarity reversed by the stronger ones.
This is counteracted to some extent by separation.

Magnet, Long Coil.
A high resistance electro-magnet; one whose coil is of thin wire of
considerable length.

Magnet, Natural.
The lodestone, q. v.; a variety of magnetite or magnetic oxide of iron,
exhibiting permanent magnetism, attracting iron, and possessing north
and south poles.

Magnet, Neutral Line of.
A line at right angles to the magnetic axis of a magnet, q.v., and
nearly or quite at the centre, so situated with reference to the poles
on either end that it marks the locus of no polarity. It has been called
the equator of the magnet. It is defined by the intersection of the
plane of no magnetism with the surface of the bar.

Synonym--Magnetic Equator.

Magnet, Normal.
A bar or compound bar magnet, magnetized to such an extent that the
curves of the lines of force run into each other in the middle, is thus
termed by Jamin.

Abbreviation for Magneto-electric Generator. (See Magneto-electric

Magneto Call Bell.
A call operated by current from a magneto-electric generator. It is very
generally used in telephone systems.


Magneto-electric. adj.
Relating to induced electric effects due to the cutting of true magnetic
lines of force by, or equivalent action of or upon a conductor. These
effects are identical with electro-magnetic effects and are only
distinguished from them by the field being due to a permanent magnet
instead of an electromagnet.

Magneto-electric Brake.
A device for bringing to rest an oscillating galvanometer needle. It
consists essentially of a coil in circuit with a key and with the
galvanometer. On opening the circuit an inverse current is established
by induction, tending to bring the needle to rest.

Magneto-electric Generator.
A current generator operating by maintaining a potential difference at
its terminals, by reactions in a field of force, which field is
established by a permanent magnet.

The cut, Fig. 230, shows the general principle of construction of a
direct current generator. The armature is rotated between the poles of a
permanent magnet. Any of the regular types of dynamo armature can be
used. From its commutator the current is taken by brushes.




The cut, Fig. 231, shows an alternating current machine. In it a pair of
bobbins, wound in series, and both either right-handed or left-handed,
are rotated between permanent magnet poles. The current may be taken off
by two brushes bearing on two collecting rings on the axis of the
bobbins, the ends of the wire being connected thereto. Or if a shocking
current is desired, one of the brushes or springs may strike a series of
pins forming virtually a broken or interrupted collecting ring. This
gives a current for medical purposes.

Synonyms--Magneto-dynamo--Magneto-electric Machine.

An apparatus for recording variations in magnetic elements. One type
includes a magnetic needle to which a concave mirror is attached. The
light ray from the mirror is reflected upon sensitized paper where its
movements are photographically reproduced. The movements of the spot are
due to the movements of the needle and act as the record of the same.

An instrument for use with a ballistic galvanometer to reproduce a
definite current impulse. Two magnets are fastened together in one
straight line, the north poles almost touching. This is mounted at the
end of a rod like a pendulum, the axis of the magnets transverse to the
rod. The magnets are carried by a frame and oscillate at the end of the
rod, back and forth within a fixed coil, which is one-half the length
of the double magnet. A bob is attached to the bottom of the frame by
which the whole can be swung. As the magnets are of fixed value, their
time of oscillation constant, and the coil fixed in size, the apparatus
provides a means of getting a definite instantaneous current of
identical value whenever needed.



(a) A reflecting galvanometer, with heavy magnetic needle, dampened by a
copper frame. It was devised by Weber.

(b) An apparatus for measuring the intensity of magnetic force. It may
consist of a magnet suspended by bifilar or by torsion suspension. A
reflecting mirror and scale as in the reflecting galvanometer may be
used to act as indicator of its motions. It is used in investigations of
the intensity of the earth's field.

If the motions of the spot of light are received on a moving strip of
sensitized paper and are thereby reproduced photographically, the
instrument is self-recording. Such an apparatus is used in the Kew
Observatory, Eng., for recording the terrestrial magnetic elements.

The determination of the magnetic moment of a magnet.

It involves the determination by experiment of--( a) the product of the
magnetic moment, M, of the magnet by the horizontal component, H, of the
earth's magnetism; (b) the quotient of M divided by H. Knowing these two
quantities, M is given by the formula M = SquareRoot( )M * H) * (M/H) )
and if desired H is given by the formula H = SquareRoot( (M*H) / (M/H)).

M*H is determined by the method of vibrations. A very long, thin magnet
suspended by a torsion filament is caused to oscillate, and its period
is determined. Calling such period T and the moment of inertia of the
magnet I, we have the formula T= 2* PI * SquareRoot( I / (H*M) )  (a),
whence H*M is calculated, I of course being known or separately



M/H is determined by the End-on deflection method, or the Broadside
deflection method. In both cases the deflection of a compass needle by
the magnet in question is the basis of the work.

In the end-on method AB is the magnet under examination; DE the compass
needle; a the angle of deflection; d  the distance between C and the
middle of AB, which should be considerable compared with the length of
DE; 2l, the length of AB. We then have the formula
   tan a = (M/H) * (2d / (d^2 - l^2)^2),
which if 2l is small compared to d reduces to
   tan a = M/Hd 3

(b), which gives M/H, a and d being known.


In the broadside method the line d is the magnetic meridian, and the
diagram shows the relative positions. We then have the formula
  tan a = (M/H) / (d2 + l2)^1.5;
which if 1 is relatively small reduces to
  tan a = M/(H * d3 )(C.)

[Transcriber's note: The image of the above paragraphs is included here.]

a and c or a and b can be combined giving M and H in C.G.S. measurement.

Magnetometer, Differential.
An apparatus, invented by Eickemeyer, for testing the magnetic qualities
of different samples of iron. It is very similar in construction and
principle to the magnetic bridge, q. v.

Magneto-motive Force.
The force producing a magnetic field or forcing lines of force around a
magnetic circuit. It is usually applied only to electro-magnets and is
expressible in turns of the wire winding multiplied by amperes of
current, or in ampere-turns.

Magnet Operation.
A term in surgery; the use of the electro-magnet or permanent magnet for
removing particles of iron from the eye.

An apparatus for detecting the presence of magnetism, without measuring
its intensity. A simple magneto-scope consists of a magnetized bit of
watch-spring suspended in a vertical glass tube by a fine filament. A
bit of unmagnetized soft iron wire may be used in the same way. The
first has the advantage of indicating polarity; the latter merely shows
magnetic attraction. A cork may be used as base of the instrument.



Magnet, Permanent.
A bar of steel charged with residual magnetism. Steel possesses high
coercive force in virtue of which when once magnetized it retains part
of the magnetization.

Permanent magnets are generally straight bars or U shaped; they are
termed bar magnets, magnetic needles, horseshoe magnets, machine magnets
and otherwise, according to their shape or uses.

Magnet Pole.
The part of a magnet showing strongest polarity; the part which attracts
iron the most powerfully, and acts as the starting point for lines of

Magnet Poles, Secondary.
Magnet poles are often not situated at the ends. Owing to inequality of
the material or other causes they may occupy intermediate positions on
the magnet. Such poles are called secondary poles.

Magnet Pole, Unit.
A unit magnet pole is one which exerts unit force on another unit pole
placed at unit distance from it. Unit force is the dyne; unit distance
is one centimeter.

Magnet, Portative Power of.
The power of sustaining a weight by attraction of its armature possessed
by a magnet. In general terms the adherence of the armature of a magnet
to the pole varies with the square of the number of lines of force which
pass through the point of contact. Hence an increased adherence of the
armature to a horseshoe electro-magnet is sometimes obtained by
diminishing the area of contact of one pole which concentrates the lines
of force. Steel magnets were frequently made with rounded ends to
increase the portative power.

Magnet, Simple.
A magnet made of one piece of metal, or at least magnetized as such; the
reverse of a compound magnet, which is magnetized piece by piece and
then fastened together.

Magnet, Solenoidal.
A magnet which is so uniformly magnetized and is so long in proportion
to its other dimensions that it virtually establishes two magnetic
poles, one at either end. It is a long thin bar so magnetized that all
its molecules would, considered as magnets, be absolutely equal.
(Daniell.) It acts like a solenoid, except that it is longer in
proportion than the solenoid generally is constructed.

Magnet, Sucking.
A magnet coil with movable or loose axial bar of soft iron.

The whole is usually mounted vertically. When a strong enough current is
passed the bar is drawn up into the coil as if by suction, whence the


Magnet, Unipolar.
No such thing as a unipolar magnet is possible. The name is given to
poised or suspended magnets, one of whose poles lies in the axis of
suspension. It is obvious that such a magnet will act, as far as its
directive tendency and rotatory movements are concerned, as if it had
only one pole. As shown in the cut, the pole s in both magnets lies in
the axis of suspension or directly under the filament by which they are
suspended, while the other pole n is the active pole in causing rotation
or directive tendency; c c are counterweights or counterpoises.


An apparatus for producing a loud sound, involving the principles of the
telephone. A rapidly alternating or make and break current being
produced by any means and being transmitted through the telephone gives
a loud note of pitch dependent on the current producing it. Sometimes a
perforated metallic disc is rotated in a magnetic field, and produces
the requisite type of current.

Magnus' Law.
A law of thermo-electricity. In a homogeneous circuit, however, the
temperature varies from point to point; there is no current.

Whatever potential differences may be established by the variations in
temperature it is evident that they must counteract each other and
reduce to zero.

Mains, Electric.
The larger conductors in a system of electric light or power

Make. v.
To complete a circuit, as by closing a switch.

Make and Break Current.
A current which is continually broken or interrupted and started again.
It is applied only where the "makes" and "breaks" succeed each other
with great rapidity, as in the action of an induction coil or pole
changer, etc. It has had considerable importance in litigation affecting
the Bell telephone patents, the courts holding that the original Bell
patent (No. 174,465, of 1876,) covered the undulating current, for the
transmission of speech. Many efforts have been made by litigants to
prove that specific telephones have transmitted articulate speech by the
make and break current, but without success. If this could have been
proved the assumption is that the courts would have sustained the use of
such device as not infringing upon the claims of the Bell patent.

A fish, sometimes called the thunder fish, an inhabitant of African
rivers, occurring in the Nile and Senegal. It possesses considerable
electric power, similar to that of the gymnotus and torpedo, although
inferior in amount.



The cistern-like depression in the ground for giving access to the ends
of tubes in electric conduits. (See Conduit, Electric Subway.)

Marked End or Pole.
The north pole or north seeking pole of a magnet, so called because it
is usually marked with a notch or scratch by the maker. The south pole
is called the unmarked end.

The quantity of matter in a body. The C. G. S. unit of mass is the
quantity of matter in a gram. While weight varies with latitude and
other circumstances, mass is invariable.

The unit of mass is also defined as the quantity of matter which in a
balance will counterpoise a standard mass, the gram or pound. As the
gram is intended to be the mass of one cubic centimeter of water at
3.09º C. (39º F.), the C. G. S. unit of mass is really 1.000013 gram.

As a primary unit its dimensions are indicated by M.

Mass, Electric.
A term for quantity of electricity. The unit mass is such a quantity as
at unit distance will act with unit force.

Matter, Electric.
The imaginary substance constituting electricity; a conception used
purely as a matter of convenience.

[Transcriber's note: The electron was discovered five years after this

Matter, Radiant.
Matter in the ultra-gaseous or so-called fourth state. In the gaseous
state the molecules of a gas are in perpetual kinetic motion, colliding
actually or virtually with each other, rebounding from such approach,
and striking also the walls of the containing vessel. But except for
these deflections, which are of enormous frequency, the paths of the
molecules would be perfectly straight.

In the radiant state matter exists in so high a vacuum that collisions
of the molecules rarely occur, and the molecules simply beat back and
forth in straight lines from side to side of the containing vessel.

A layer of gas in this condition is termed a Crookes' layer, from Prof.
William Crookes, who discovered and investigated these phenomena.


Luminous streams of the molecules are produced by electric high
potential discharges between electrodes. The course of the discharge is
normal, in general terms, to the surfaces of the electrodes, and reaches
from one to the other in a curve or straight line, as the case may be.

These luminous streams are deflected by a magnetic field; if brought to
a focus can heat refractory material in that focus to a full white heat,
and can develop phosphorescence. The latter is termed electric
phosphorescence. A great variety of experiments have been devised to
illustrate the phenomena of radiant matter. The vacuum is generally
produced in a hermetically sealed glass vessel into which the electrodes
are sealed, and which contain the phosphorescent substances or other
essentials for the experiments. The vessels are termed Crookes' Tubes.

[Transcriber's note: Crookes reported on "radiant matter" in 1879. It is
actually electrons, but he failed to distinguish them from ordinary
atoms. Thompson properly described electrons in 1897.]

Matteueci's Experiment.
An experiment for showing the inductive effect of the discharge of a
Leyden jar. Two glass plates are supported on standards in a vertical
position. Flat coils of wire are wound or coiled and secured to one
surface of each plate. One plate has much finer and longer wire than the
other. Metal handles are connected to the ends of the coarser wire coil.
The plates