ELECTRIC LIGHT, HEAT, AND POWER
For the use of the cuts in this chapter, the Publishers desire to
acknowledge the courtesy of the General Electric Company, the Thomson
Electric Welding Company, and the Cooper Hewitt Electric Company.
With the discovery of the reversibility of the dynamo, the invention of
the telephone, and the improvements in the electric light began the
great modern development of electricity which proved that marvellous
agent to be a master-workman.
Many of the things electrical that we ordinarily think of as modern
inventions are merely modern applications of phenomena that were
discovered many years ago. The pioneers in the science of dynamic
electricity performed their experiments with the electric light,
electro-magnets, etc., by using galvanic batteries. But for practical
purposes the consuming of zinc and chemicals in such batteries was too
expensive a way to generate electricity, and prevented any commercial
use of the results of their experiments until cheaper electricity could
be had.
The Work of the Dynamo
The invention of the dynamo, with which we obtain electricity from
mechanical power, changed all that. Instead of consuming zinc in
primary batteries, men could obtain it by burning coal, which is much
cheaper, under the boiler of a steam-engine used to drive the dynamo.
Thus it is that modern electricity comes from mechanical power. It is
really the energy of a steam-engine or a water-wheel, or some other
“prime mover,” working through the medium of electricity, that is
transmitted to a distance and distributed over wires. The electricity
may then be transmuted into light, heat, or chemical energy as the case
may be, to light our electric lamps, develop the intense heat of the
electric furnace, and charge storage-batteries.
Moreover, some time after the invention of the dynamo it was found that
the mechanical power put into one of these machines could be transmitted
electrically and reproduced as mechanical power. In other words, a
dynamo could be made to revolve and give out power, as a motor, by
supplying it with current from another dynamo. This showed the way to
transmute electricity back again into mechanical power, to run our
electric cars and trains, and all kinds of machinery in our factories
and elsewhere. Nowadays the dynamo is used to generate nearly all the
electricity that we need. Even in such comparatively old electrical
applications as electro-plating and the telegraph and telephone, primary
batteries are being supplanted by motor dynamos, which we shall learn
about later.
It is from the invention of the dynamo and the discovery that it was
reversible that we date the beginning of what are known as heavy
electrical engineering applications, including electric light, heat, and
power. In this closing chapter it is purposed to learn a little about
these applications, and in so doing to summarize briefly the things that
we have already studied.
The Electric Light
In the chapter on Electrical Resistance we learned that an electric
current always encounters a resistance in passing through a conductor,
and that when the current is strong enough the conductor is heated up.
The electric light is produced by the heating of a conductor of one kind
or another to incandescence by the electrical friction of the current
passing through it.
The first electric light was made by Sir Humphry Davy over a hundred
years ago. He discovered that when a current from a great many cells of
battery was interrupted the spark did not simply appear for an instant
and then go out, as it does when only a few cells are used, but remained
playing between the terminals of the circuit. He found by experiment
that if pieces of carbon are used as the terminals--or “electrodes,” as
they are called--the electricity passes between them in an intensely hot
flame, or “arc.” The latter, which is due to the electrical resistance
of the vapor of carbon, heats up the carbon-points so that they give a
brilliant white light.
[Illustration: _=Fig. 1=_]
[Illustration: _=Fig. 2=_]
Before the dynamo came into use, the electric light was rarely seen,
except as a philosophical experiment; but as soon as cheap electricity
became available, commercial electric arc-lamps were made by many
inventors and have been continually improved. Fig. 1 shows one form of
modern arc-lamp, with its case removed to show the interior mechanism.
In most arc-lamps the lamp itself consists of a pair of carbon or other
electrodes in the form of long rods arranged vertically, with their tips
normally in contact. When the current is turned on, the mechanism lifts
the upper electrode away from the lower one. The interruption of the
circuit thus caused “strikes the arc” between the tips, and the
mechanism keeps the arc-distance unchanged as the carbons burn away.
Some arc-lamps are made to burn on continuous-current, and others on
alternating-current circuits. When continuous current is used, the upper
(or positive) carbon burns away about twice as fast as the lower one,
forming a cup, or “crater,” from which most of the light comes.
Uses of the Arc-Light
The first commercial use of the arc-light on a large scale was for
street-lighting, to replace the old-fashioned gas-lamps. But another
important use is in search-lights, in which the arc-lamp is fitted with
a powerful reflector for throwing a very bright light to a distance.
Fig. 2 is a view of a search-light arranged to go on top of a ship’s
pilot-house. In war-time the ships carry search-lights to help them find
the enemy’s ships and repel attack; and they are used in the army also,
by having a portable dynamo and engine drawn by horses. The arc is also
employed in projectors for lecture-rooms, and sometimes for the
headlights of steam and electric locomotives and interurban electric
cars.
Incandescent and Other Lamps
The arc-lamp came into wide use for lighting large spaces like streets,
stores, and public halls, but was found to be too intense for lighting
smaller places like private houses. After many experiments, Edison
succeeded in subdividing the electric light into the small pear-shaped
“incandescent” lamps that we now see everywhere. In this kind of
electric lamp the light comes from a thin “filament” of carbon,
contained in a glass globe from which all air has been removed. Since
there is no oxygen to support combustion, the filament may be heated
white-hot by the current without being consumed.
[Illustration: _=Fig. 3=_]
In certain other forms of incandescent lamps that are just coming into
use, the filaments are made of rare metals--osmium, tantalum, etc.--that
will stand a high temperature without melting. The Nernst lamp has a
filament consisting of a mixture of certain materials that has to be
heated before it will conduct electricity.
Then there are the so-called “vapor” lamps, consisting of a glass tube
full of conducting metallic vapor which gives out light when a current
is passed through it. The best-known form is the Cooper Hewitt mercury
vapor-lamp shown in Fig. 3, which gives a peculiar greenish light.
From the point of view of efficiency, the electric light, wonderful as
it is, leaves much to be desired. The light always comes from a hot
resistance; and whether this resistance is a mass of conducting vapor,
as in the arc and vapor lamps, or a solid conducting filament, as in the
so-called “incandescent” lamps, much more heat than light is produced. A
needed improvement, therefore, is in the direction of obtaining a
greater percentage of light for a given amount of electrical energy.
Electric Heat
The generation of heat in electrical devices usually means wasted
energy--sometimes a very serious waste, as we have just seen. There are
certain kinds of electrical apparatus, however, that are designed to
transform all of the electrical energy delivered to them into heat, for
various industrial and household purposes.
[Illustration: _=Fig. 4=_]
Electric Furnaces
By far the most important application of electric heat, as such, is in
electric furnaces, by means of which we attain the highest temperatures
known to man. The electric furnace consists of a chamber of “refractory”
material, containing the substances to be acted upon by the heat, with a
pair of big carbon electrodes thrust into the centre, as shown in Fig.
4, which is a picture of Moissan’s electric furnace for the distillation
of metals, and supplied with heavy continuous or alternating currents.
The apparatus is therefore a sort of gigantic electric arc-lamp, so
enclosed that the whole of the intense heat of the arc is confined and
concentrated on the smelting or other work. In many places where cheap
electric power is to be had--as in the vicinity of the great Niagara
Falls power-plants--electric furnaces are employed in what are known as
electrometallurgical and electrochemical manufacturing processes. By
their aid many metals and other substances that were formerly scientific
curiosities, or entirely unknown, are produced commercially; such as
aluminum, certain rare metals, and calcium carbide, from which that
wonderful illuminant, acetylene-gas, is obtained.
Welding Metals
Another useful application of electric heat is in the welding of metals.
Instead of heating the pieces to be welded in a forge, their ends are
simply butted together and the electricity--generally from an
alternating-current transformer--turned on. The heat developed by the
“contact resistance” between the pieces quickly softens the metal so
that the pieces may be forced together, forming a perfect weld in a few
minutes without any hammering. Fig. 5 is a view of one form of electric
welding-machine in which this is accomplished. The electric process can
weld certain metals that cannot be joined securely by ordinary welding
methods, and is used in several special arts.
Welding is also performed by the heat of a special electric arc-lamp,
which a workman holds in his hand like a blow-pipe or torch. This
process is especially useful in joining the edges of sheet-steel, in
making tanks for electric “transformers,” etc. The workmen have to wear
smoked glasses in order to protect their eyes from the intense glare of
the arc.
[Illustration: _=Fig. 5=_]
Electric Car-heaters
Perhaps the simplest and best-known application of electric heat is the
electric car-heater, consisting of coils of high-resistance wire--such
as iron or German-silver wire--mounted on an insulating, non-combustible
frame which is placed under the seats of the car. Part of the current
from the trolley wire or third rail passes through the resistance-coils,
heating them up and thereby warming the air in the car.
Household Uses
Nowadays electric heat is being more and more widely utilized in what
are known as household electric heating-appliances. One of the most
useful of these is the electric flat-iron, shown in Fig. 6. This
flat-iron is designed to do away with the use of a hot stove of any
kind, and is internally heated by means of a resistance-coil of peculiar
shape placed in the bottom of the iron close against its working face.
The iron is connected to an electric-light socket by means of an
attaching plug on the end of a long, flexible cord. It takes only a few
minutes to get hot, and its use saves much time and labor.
The list of special heating-appliances that are now made includes
curling-iron heaters; heating-pads, for taking the place of hot-water
bags in the sick-room; cigar-lighters, in which a little grid
“resistance” is made incandescent by pressing a button; foot-warmers;
and radiators to dry wet shoes or skirts on rainy days. For industrial
use there are glue-pots, for bookbinders and pattern-makers; large
flat-irons, for tailor-shops and laundries; and electric ovens, for
drying certain parts of electrical machines and for cooking various
kinds of “prepared foods.”
Many electric cooking-utensils are made for the household, such as
coffee-percolators, egg-boilers, ovens, disk stoves, etc. Each one is
equipped with a resistance-coil like that in the electric flat-iron just
described, so that it contains its own source of heat, which is under
perfect control by means of a switch. An “electric kitchen” consists of
a number of these utensils, wired to a convenient table or stand, as
shown in Fig. 7.
[Illustration: _=Fig. 6=_]
[Illustration: _=Fig. 7=_]
Electric Power
We have seen that the modern way to generate electricity is from
mechanical energy applied through a dynamo, and that the “electric
power” thus generated may be transmitted over wires to a distance and
there transformed into other forms of energy, such as light, heat, and
chemical energy, or reproduced again as mechanical energy. The last
mentioned of these transformations is the most important of them all,
because it is the one that means the most for the advancement of
civilization. Before the invention of the dynamo and the discovery that
it was reversible, mechanical power could be employed only in the place
where it was generated, so that its use was restricted; whereas nowadays
the field of power is broadened and its cost reduced by electrical
transmission and distribution.
In the chapter on Dynamos and Motors we learned how to make and use
those machines. Let us review, very briefly, just what happens in the
double transformation--of mechanical energy into electricity and then
back again at the end of a line of wires--that we call electric-power
transmission. In the dynamo, the power of the water-wheel, or whatever
other prime mover is used, is exerted in generating electricity by
forcing the electric conductors of the machine through a magnetic field.
The electricity is led away to a distance--a hundred miles, perhaps--by
wires and allowed to enter another machine similar to the dynamo, but
operating as a motor. Here the first process is reversed: the
electricity passing through the conductors of the motor reacts upon its
magnetic field, causing the machine to revolve and thus generating
mechanical power again. The line-wires carry the power just as
positively as though a long shaft ran from the prime mover to the
receiving end of the line, and much more economically. The action that
goes on is similar to the operation of the telephone--which is indeed a
special case of electric-power transmission--as already explained in a
former chapter: the sound of the voice being transformed, at the
telephone-transmitter, into electrical energy in the form of alternating
currents, then carried as such over the line and finally reproduced as
sound again at the receiver.
Power from Water-wheels
“Hydro-electric” transmissions--i. e., electric transmissions of power
from a water-wheel as prime mover--are the most important because they
bring into use cheap water-power that formerly ran to waste. There are
many hydro-electric transmissions in this country, Mexico, and Canada,
some of them utilizing the power of waterfalls or rapids located in
mountainous and inaccessible parts. The alternating current is nearly
always used because by it men can much more easily and safely generate,
transmit, and receive the high voltages that have to be used than by the
continuous current. The machinery at the “main generating station”
consists of big alternating-current dynamos, which sometimes have
vertical shafts instead of horizontal ones, so that they may be driven
directly by turbines. The current is generated at a moderate potential,
which is then “stepped-up,” by “static transformers,” to the
comparatively high-line voltage that is required in long-distance
transmissions.
[Illustration: _=Fig. 8=_]
Transformers
Fig. 8 is a view of a very large transformer of over 2500 electrical
horse-power capacity. In the picture the containing-tank is represented
as transparent, so as to show the transformer proper inside. The latter
is really a special kind of induction-coil, with primary and secondary
windings, and a core, weighing many tons, built up of thin sheets of
steel. In this kind of transformer, the tank is filled with oil, to
keep the transformer cool in operation, and to help insulate it against
the high potential to which it is subjected. At the receiving end, or
“sub-station,” the high-voltage electric power enters a set of
“step-down” transformers, from which it is delivered again, at moderate
potential, to the motors.
Sometimes power is distributed from a single great generating station to
several sub-stations. In the Necaxa transmission, in Mexico, over 35,000
horse-power is taken from a waterfall in the mountains and transmitted
at 60,000 volts potential to Mexico City, 100 miles away, and to the
mining town of El Oro, seventy-four miles farther on.
Several kinds of motors are used at the receiving end of electric-power
transmission-lines, according to the work that they are called upon to
do. For “stationary” work, like driving the machines in mills and
factories, two principal kinds of alternating-current motors are
employed--synchronous and induction motors. The former are built just
like alternating-current dynamos, and when they are running they keep
“in step” with the dynamo at the other end of the line; i. e., the
motion of their field windings relatively to their armatures keeps exact
pace with the same motion at the dynamo, just as though a long shaft ran
from one machine to the other instead of the electric wires of the
transmission-line. A motor of this type, at work driving an
air-compressor, is shown in Fig. 9. The induction-motor is really a sort
of transformer, the primary winding of which is the fixed part, or
field, and the secondary winding the rotating armature. It does not keep
in step with the dynamo, like the synchronous motor, but adapts its
speed to the “load,” or amount of work that it is called upon to do,
like a continuous-current motor.
[Illustration: _=Fig. 9=_]
Rotary Converters
Sometimes alternating-current electric power is transformed at the
sub-station into continuous-current power. This is done by a special
kind of transformer called a “rotary converter.” The static transformers
of which we have just been speaking are built, like ordinary
reduction-coils, with no moving parts, and operate by taking in
alternating currents at a given potential and giving out alternating
currents at a different potential, higher or lower as the case may be.
The rotary converter, however, is built something like a dynamo, with a
stationary field and a revolving armature, and ordinarily operates by
receiving an alternating current at a given potential and delivering a
continuous current of the same or a different potential. This kind of
transformation is employed wherever it is desired to obtain any large
amount of continuous current from an alternating-current
transmission-line; and especially to obtain “500-volt continuous
current” for operating street and interurban electric railways, as we
shall see under the next heading. Fig. 10 shows one form of rotary
converter built for supplying continuous current for trolley service.
[Illustration: _=Fig. 10=_]
Oftentimes the sub-station of a transmission system contains both static
transformers and rotary converters, to supply both alternating current
and continuous current from the same high-voltage alternating-current
line. When the continuous current has to be transformed from one voltage
to another, a “motor dynamo” is used, consisting of an electric motor
driving a dynamo on a common shaft.
One of the most interesting features of electric-power transmission is
the care that is taken to avoid the terrible danger from the high
potentials, and at the same time prevent loss of power on the way. The
electricity in the machinery and in the line-wires that extend across
the country is veritable lightning, and has to be carefully guarded from
doing any damage or escaping. To prevent leakage, the insulation of all
of the station machinery and apparatus is made extra good, with “high
dielectric strength,” so that it will not be punctured by the high
voltage; and the line-insulators are made very large, and electrically
and mechanically strong--quite unlike the ordinary-sized glass or
porcelain insulators that are employed for telegraph and telephone
lines. Each insulator before being put up is tested under a “breakdown
voltage” much higher than it is to stand in actual service.
Oil-switches
The switching of high-voltage electric power is a knotty problem. The
circuit cannot be interrupted by “air-break” switches, such as are used
in ordinary electric-light stations, for any attempt to do so would
result in a destructive arc many feet long, that could not be
extinguished. Therefore “oil-switches” are always used to control the
line-circuits at the main generating station and the sub-stations. In
these oil-switches--which are designed to be operated from a distance,
by hand-levers, or sometimes by electric motors--the circuit is made and
broken under the surface of oil, which prevents the formation of an
arc. Moreover, the switchboard attendant does not have to come anywhere
near the deadly high-voltage wires, but can make the necessary
connections at a safe distance.
Electric Traction
The use of the electric motor to propel vehicles of all kinds is called
electric traction. It is, of course, a branch of electric power, which
we have just been considering; and it is in many respects the most
important branch. The wealth of a country is largely built up and
maintained by its facilities for transportation, such as its canals,
highways, railroads, and street and interurban car-lines.
In this field electric power is playing a most important part, although
it was not many years ago that the first experimental electric cars were
put in to replace horses on the street-railways of our cities. The
change was found to be so successful that the field of the trolley-car
was widened and extended very rapidly, until now we have our great
suburban and interurban electric railways, with cars almost or quite as
big as those on the steam-railroads and running at even higher speeds.
During the last few years, also, the sphere of the steam-railroad itself
has been invaded by electricity, by the construction of powerful
electric locomotives to draw passenger and freight trains.
The Trolley-car
Let us consider just what it is that makes a trolley-car go. Since
electric power is only mechanical energy in another form, we know that
the motionless copper trolley-wire, suspended over the track in our
streets, is the means of propelling the car just as truly--though in a
different way--as if it were a moving steel cable to which the car was
attached. We must keep in mind the fact that the electricity is not
itself the source of power, but only the medium of transmission. The
engine in the power-house, by turning a dynamo there, maintains a
constant electric pressure, or “constant potential,” as it is termed, in
the trolley-wire. This pressure of electricity forces the power through
the motors of the car as soon as the motorman makes the connection to
them by turning the handle of his “controller.”
[Illustration: _=Fig. 11=_]
The Continuous-current Motor
Fig. 11 is a view of one form of continuous-current motor. There is not
much of the motor itself to be seen, because it is entirely enclosed in
a cast-iron case. The shaft of the motor has a small “spur gear” fixed
on one end, driving a gear-wheel which is fixed on the car axle. By this
arrangement more than one revolution of the motor armature is required
to make one revolution of the car-wheel, which multiplies the force
exerted in turning the wheel.
[Illustration: _=Fig. 12=_]
The Controller
Fig. 12 is a view of a type of controller that is used on the platform
of trolley-cars. The cover is removed to show the contacts, inside, by
which the electric power is turned on gradually by the controller
handle. The trains of electric cars that run on the elevated structures
and in the subways of our large cities are supplied with power from a
“third rail” placed by the side of the track, on insulating supports,
and the motors on all the cars are controlled from a single
“master-controller” on the front platform of the forward car. This
system of control, known as the “multiple-unit” system, gives electric
trains several advantages over the old kind, drawn by steam-locomotives;
such as they used to have on the New York elevated roads, for example.
For one thing, the train can be started much more quickly, since all the
motors begin to turn the car-wheels at the same instant. Then again, the
system enables a long train of cars to be controlled as easily as a
single car, and better “traction” between wheels and track is obtained.
Electric Locomotives
Several of the great steam-railroads are now adopting the electric
locomotive to draw their trains. Fig. 13 is a view of one of the great
continuous current electric locomotives that are used by the New York
Central Railroad to handle many of its passenger-trains in and out of
the Grand Central Station, in New York city. The motors of this
powerful electric engine, unlike those of trolley-cars, are “gearless”;
that is, their armatures are fixed directly on the locomotive axles so
that they revolve at the same speed as the driving-wheels.
[Illustration: _=Fig. 13=_]
All of the railway motors considered thus far have been of the
continuous-current type, although the current to operate them is often
obtained from alternating current transmission-systems, through rotary
converters, as described above. The alternating current is also
beginning to be employed to drive cars and trains. One type of
alternating current railway motor, designed for “single-phase”
operation, is in use on several interurban systems in this country,
running on high-voltage alternating current most of the time, but on
continuous current when within the city limits.
Other Forms of Electric Traction
Electric traction also includes electric automobiles, supplied by
storage-batteries; a slow-speed electric locomotive for drawing
canal-boats, and called “the electric mule”; and an ingenious
gasolene-electric outfit for driving cars by electric motors without any
trolley, third rail, or storage-battery. The last-mentioned arrangement
consists of a set of electric car-motors mounted on the trucks in the
usual way, but supplied with current by a dynamo mounted on the car
itself and driven by a gasolene-engine. Thus the car carries its own
power-station about with it, and is independent of any outside source of
electricity.
* * * * *
The old alchemists sought to transmute _matter_ from one form to
another; and especially lead and other “base metals” into gold, in order
that they might grow rich by concentrating the precious metal in their
own selfish hands. The modern miracle that electricity works for us, the
transmutation of _energy_, is a higher and broader thing, because it
multiplies and distributes the world’s good things.
APPENDIX
A DICTIONARY OF ELECTRICAL TERMS AND PHRASES
Everybody is interested in electricity, but the ordinary reader, and
particularly the boy who attempts to use this manual intelligently, will
come across many technical words and terms that require explanation. It
would be impossible to incorporate all needful definitions in the text
proper, and the reader is therefore referred to the technical dictionary
on the succeeding pages.
Care has been taken in its compilation to make the definitions complete,
simple, and concise. Some of the more advanced technical terms have been
purposely omitted as not necessary in a book dealing with elementary
principles. The student in the higher branches of the science will
consult, of course, the more advanced text-books. But for our practical
purposes this elementary dictionary should answer every requirement. To
read it over is an education in itself, and the young experimenter in
electrical science should always refer to it when he comes across a word
or phrase that he does not fully understand.
A
=A.= An abbreviation for the word anode.
=Absolute.= Complete by itself. In quantities it refers to fixed units.
A galvanometer gives absolute readings if it is graduated to read direct
amperes or volts. An absolute vacuum is one in which all residual gases
are exhausted; an absolute void is the theoretical consequent. The
absolute unit of current is measured in one, two, three, or more amperes
or volts.
=A-C.= An abbreviation expressing alternating current.
=Acceleration.= The rate of change in velocity.
The increase or decrease of motion when acted upon by the electric
current.
=Accumulator.= A term applied to a secondary battery, commonly called a
storage-battery.
=Accumulator, Electrostatic.= (_See_ Electrostatic Accumulator.)
=Accumulator, Storage.= A storage-battery.
=Acid.= A compound of hydrogen capable of uniting with a base to form
salts.
Sour, resembling vinegar.
A sharp, biting fluid.
=Acidometer.= A hydrometer used to determine the gravity of acids. It is
employed chiefly in running storage-batteries to determine when the
charge is complete.
=Adapter.= A screw-coupling to engage with different size screws on
either end, and used chiefly to connect incandescent lamps to
gas-fixtures.
=Adherence.= The attraction between surfaces of iron due to
electro-magnetic action. The term is used in connection with electric
brakes--electro-magnetic adherence.
=Adjustment.= Any change in an apparatus rendering it more efficient and
correct in its work.
=Aerial Conductor.= A wire or electric conductor carried over housetops
or poles, or otherwise suspended in the air, as distinguished from
underground or submarine conductors.
=Affinity.= The attraction of atoms and molecules for each other, due to
chemical or electrical action.
=Air-condenser.= A static condenser whose dielectric is air.
=Air-line Wire.= In telegraphy that portion of the line-wire which is
strung on poles and carried through the air.
=Alarm, Burglar.= A system of circuits with an alarm-bell, the wires of
which extend over a house or building, connecting the windows and doors
with the annunciator.
=Alarm, Electric.= An appliance for calling attention, generally through
the ringing of a bell or the operating of a horn.
=Alarm, Fire and Heat.= An expansion apparatus that automatically closes
a circuit and rings a bell.
=Alive, or “Live.”= A term applied to a wire or circuit that is charged
with electricity. A “live” wire.
Active circuits or wires.
=Alloy.= Any mixture of two or more metals making a scientific compound.
For example: copper and zinc to form brass; copper, tin, and zinc to
form bronze; copper, nickel, and zinc to form German-silver.
=Alternating Current.= (_See_ Current, Alternating.)
=Alternating Current-power.= Electrical distribution employing the
alternating current from dynamos or converters.
=Alternation.= A change in the direction of a current; to and fro.
Alternations may take place with a frequency ranging from 500 to 10,000
or more vibrations per second.
=Alternator.= An electric generator-dynamo supplying an alternating
current.
=Amalgam.= A combination of mercury with any other metal.
=Amalgamation.= The application of mercury to a metal, the surface of
which has been cleansed with acid. Mercury will adhere to all metals,
except iron and steel, and particularly to zinc, which is treated with
mercury to retard the corrosive action of acid on its surface.
=Amber.= A fossil resin, valuable only in frictional electric
experiments. Most of it is gathered on the shores of the Baltic Sea
between Königsberg and Memel. It is also found in small quantities at
Gay Head, Massachusetts, and in the New Jersey green sand. When rubbed
with a cloth it becomes excited with negative electricity.
=Ammeter.= 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.
=Ampere.= 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.
=Ampere-currents.= The currents theoretically assumed to be the cause of
magnetism.
=Ampere-hour.= The quantity of electricity passed by a current of one
ampere in one hour. It is used by electric light and power companies as
the unit of energy supplied by them, and on which they base their
reckoning for measuring the charges for current consumed.
=Ampere-ring.= A conductor forming a ring or circle. Used in electric
balances for measuring current.
=Animal Electricity.= A form of electricity of high tension generated in
certain animal systems--the Torpedo, Gymnotus, and Célurus. The shocks
given by these fish, and particularly the electric eel, are often very
severe.
=Annealing.= The process of softening yellow metals by heating them to a
cherry redness, then allowing them to cool gradually in the air.
Electric annealing is done by passing a current through the body to be
annealed, and heating it to redness; then allowing it to cool gradually.
=Annunciator.= An apparatus for giving a call from one place to another,
as from a living-room to a hotel office, or for designating a window or
door that may have been opened when protected by a burglar-alarm.
=Annunciator-drop.= The little shutter which is dropped by some forms of
annunciators, and whose fall discloses a number or letter, designating
the location from which the call was sent.
=Anode.= The positive terminal in a broken, metallic, or true conducting
circuit.
The terminal connected to the carbon-plate of a battery, or to its
equivalent in any other form of electric generator, such as a dynamo or
a voltaic pile.
The copper, nickel, gold, or silver plates hung in an electro-plating
bath, and from which the metal is supplied to fill the deficiency made
by the electro-deposition of metal on the kathode or negative object in
the bath.
=Anti-hum.= A shackle inserted directly in a line-wire near a pole. It
is provided with a washer or cushion of rubber to take up the vibrations
of a wire. To continue the circuit a bridle, or curved piece of wire, is
connected with the line-wires that are attached to the shackle.
=Arc.= A term applied to an electric current flowing from carbon to
carbon, or from metals separated by a short gap, as in the arc
street-lamps.
The original arc was produced by two vertical rods, through which the
current passed up and down. When not in action the upper ends touched,
but as the current flowed the ends were separated, so that the current,
passing up one carbon across the gap and down the other, formed the
segment of a circle in jumping from one tip to the other.
An arc of electric flame is of brilliant and dazzling whiteness. The
voltaic arc is the source of the most intense heat and light yet
produced by man. The light is due principally to the incandescence of
the ends of carbon-pencils, when a current of sufficient strength is
passing through them and jumping over the gap. Undoubtedly the
transferred carbon particles have much to do with its formation. The
conductivity of the intervening air and the intense heating to which it
is subjected, together with its coefficient of resistance, are other
factors in the brilliant light produced.
=Arc-lamp.= An electric lamp which derives its light from the voltaic
arc, by means of carbon-pencils and a current jumping from one to the
other.
=Arc, Quiet.= An arc free from the hissing sound so common in
arc-lights.
=Arc, Simple.= A voltaic arc produced between only two electrodes.
=Armature.= A body of iron or other material susceptible to
magnetization, and which is placed on or near the poles of a magnet.
That part of an electric mechanism which by magnetism is drawn to or
repelled from a magnet.
The core of a dynamo or motor which revolves within the field magnets,
and which is the active principle in the generation of current by
mechanical means, or in the distribution of power through electrical
influence. Armatures are sometimes made of steel, and are permanent
magnets. These are used in magneto-generators, telegraph instruments,
and other apparatus.
=Armature-bar.= An armature in a dynamo or motor whose winding is made
up of conductors in the form of bars.
=Armature-coil.= 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 is
wound; it is rotated in the field of an electric current-generator or
motor.
=Armored.= Protected by armor; as cables may be surrounded by a proper
sheathing to guard them from injury.
=Astatic.= Having no magnetic directive tendency, the latter being a
general consequent of the earth’s magnetism.
=Astatic Circuit.= (_See_ Circuit, Astatic.)
=Astatic Couple.= (_See_ Couple, Astatic.)
=Astatic Needle.= A combination of two magnetic needles so adjusted as
to have as slight directive tendency as possible. The combination is
generally made up of two needles arranged one above the other with the
poles in opposite directions--commonly called “Nobili’s Pair.” These
needles require but a slight electro-force to turn them one way or the
other, and are used in astatic galvanometers.
=Atmospheric Electricity.= (_See_ Electricity, Atmospheric.)
=Atom.= The ultimate particle or division of an elementary substance.
Electricity is largely responsible for the presence of atoms in the
atmosphere.
=Atomic Attraction.= The attraction of atoms for each other. Principally
due to electric disturbance.
=Attraction.= The tendency to approach and adhere or cohere which is
shown in all forms of matter. It includes gravitation, cohesion,
adhesion, chemical affinity, electro-magnetic and dynamic attraction.
=Aurora.= A luminous electric display seen in the northern heavens. It
is commonly thought to be the electric discharges of the earth into the
atmosphere, due to revolution of the former and to the heat produced at
the equator. As compared to the static machine for generating frictional
electricity, the earth represents the revolving wheel gathering the
current and discharging it at the poles.
=Automatic Cut-out.= An electro-magnetic switch introduced into a
circuit, so as to break the circuit of the latter should it become
overloaded with current; it also acts in the event of a mechanical
interruption.
=Automatic Regulation.= A speed regulator worked by electricity so that
a uniform flow of current may be secured automatically.
=Ayrton’s Condenser.= This is a pile of glass plates separated by small
pieces of glass at the four comers, so that the plates cannot touch each
other. Tin-foil is pasted on both sides of every plate, and the two
coatings are connected. The tin-foil on each second plate is smaller in
area than that on the others, and the plates are connected in two sets,
negative and positive. In this construction it will be seen that the
glass is not the dielectric proper, but acts only as the plane to which
the tin-foil is pasted. One set of plates are connected to a
binding-post by strips of tin-foil, and the other set are connected to
another binding-post in a similar manner.
B
=B.= An abbreviation for Beaumé, the inventor of the hydrometer scale.
Thus, in speaking of the gravity of fluids, 20° B. means twenty degrees
Beaumé.
=Back Induction.= A demagnetizing force produced in a dynamo when a lead
is given to the brushes. (_See also_ Induction, Back.)
=Back Shock.= A lightning stroke received after the main discharge. It
is caused by a charge induced in neighboring surfaces by the main
discharge.
=Bad Earth.= A poor ground connection, or one having comparatively
strong electrical resistance.
=Balance.= A proper adjustment between the apparatus and the
electro-motive force, thus securing the best possible results.
=B. & S. W-G.= Abbreviations for Brown & Sharp and wire-gauge, and
referring to the sizes of wire and sheet-metal thicknesses that are
considered standards in America.
=Bar-armature.= An armature in which the conductors are constructed of
bars.
=Bar-magnet.= One whose core presents the appearance of a straight bar,
or rod, without curve or bend.
=Bare-carbons.= Electric light carbons whose surfaces are not
electro-plated with copper.
=Barometer.= An apparatus for measuring the pressure exerted by the
atmosphere. It consists of a glass tube 31 inches long, closed at one
end, filled with mercury, and then inverted, with its open end immersed
in a cistern of mercury. The column of mercury falls to a height
proportional to the pressure of the atmosphere. At the sea-level it
ranges from 30 to 31 inches.
=Bar-windings.= The windings of an armature constructed of copper bars.
=Bath.= In electro-plating, the solution or electrolyte used for
depositing metal on the object to be plated. It may be a solution of
copper, silver, nickel, or other metal.
In electro-therapeutics it is a bath of water with suitable electrodes
and connections for treating patients with electricity.
=Bath-stripping.= A solution used for stripping or removing the metal
plating from an object.
=Batten.= A strip of wood grooved longitudinally, in which electric
light or power wires are set. The grooved strip is screwed to the wall,
the wires being laid in the grooves, and then covered with a thin wooden
strip fastened on with small nails.
=Battery.= A combination of parts, or elements, for the production of
electrical action.
A number of cells connected parallel or in series for the generation of
electricity. Under this heading there are at least one hundred different
kinds. Nowadays the dynamo is the cheap and efficient generator of
electricity.
=Battery Cell, Elements of.= The plates of zinc and carbon, or of zinc
and copper, in a cell are called elements. The plate unattacked by the
solution, such as the carbon or copper, is the negative element, while
the one attacked and corroded by the electrolyte is the positive.
=Battery, Dry.= A form of open circuit cell in which the electrolyte is
made practically solid, so that the cell may be placed in any position.
A zinc cup is filled with the electrolyte and a carbon-rod placed in the
middle, care being taken to avoid contact between cup and carbon at the
bottom of the cell. The gelatinous chemical mass is then packed in
closely about the carbon, so as to nearly fill the cup. A capping of
asphaltum, wax, or other non-conducting and sealing material is placed
over the electrolyte, and this hardens about the carbon and around the
top inner edge of the zinc cup. The latter becomes the positive pole,
the carbon the negative. Binding-posts, or connections, may be attached
to the zinc and carbon to facilitate connections.
=Battery, Galvanic.= The old name for a voltaic battery.
=Battery, Gravity.= A battery in which the separation of fluids is
obtained through their difference in specific gravity--for example, the
bluestone cell. The sulphate of copper solution, being the more dense,
goes to the bottom, while the zinc solution stays at the top. In its
action the acid at the top corrodes the zinc, while at the bottom the
solution is decomposed and deposits metallic copper on the thin copper
plates.
=Battery, Leclanché.= An open circuit battery consisting of a jar, a
porous cup, and the carbon and zinc elements, the electrolyte of which
is a solution of ammonium chloride (sal-ammoniac). The carbon plate is
placed in the porous cup, and packed in with a mixture of powdered
manganese binoxide and graphite, to serve as a depolarizer. A
half-saturated solution of sal-ammoniac is placed in the outer jar, and
a rod of zinc suspended in it. Another form of the battery is to omit
the porous cup and use twice the bulk of carbon, both elements being
suspended in the one solution of sal-ammoniac; this form of battery is
used for open-circuit work only, such as bells, buzzers, and
annunciators. It is not adapted for lights, power, or plating purposes.
=Battery Mud.= A deposit of mud-like character which forms at the bottom
of gravity batteries, and which consists of metallic copper precipitated
by the zinc. It only occurs where wasteful action has taken place.
=Battery of Dynamos.= A term used in speaking of a number of dynamos
coupled to supply the same circuit. They may be coupled in series or
parallel.
=Battery, Plunge.= A battery in a cabinet or frame, so arranged that the
active plates can be removed or raised out of the solutions. This is
usually accomplished by having the plates attached to a movable frame
which, by means of a ratchet-shaft and chains, can be raised or lowered.
Its object is to prevent the corrosion of the plates when not in use.
=Battery, Primary.= A voltaic cell or battery generating electric energy
by direct consumption of material. The ordinary voltaic cell, or
galvanic battery, is a primary battery.
=Battery, Secondary.= A storage-battery, an accumulator.
=Battery Solution.= The active excitant liquid, or electrolyte, placed
within a cell to corrode the positive element. Also called
Electropoion.
=Battery, Storage.= A secondary battery; an accumulator; a battery which
accumulates electricity generated by primary cells or a dynamo.
=Battery-gauge.= A galvanometer used for testing batteries and
connections. It is usually small in size, and may be carried in a
pocket.
=Battery-jar.= A glass, earthen, or lead vessel which contains the
fluids and elements of each separate cell of a battery.
=Baumé Hydrometer.= (_See_ Hydrometer, Baumé.)
=Becquerel Ray and Radiation.= An invisible ray discovered by Becquerel,
which is given out by some compounds and chemicals--notably uranium--and
which has the power to penetrate many opaque bodies and objects
impenetrable to the actinic rays of ordinary light. These rays are used
chiefly in connection with the photographic dry-plate.
=Bell, Electric.= A bell rung by electricity. The current excites an
electro-magnet, attracting or releasing an armature which is attached to
a vibrating or pivoted arm, on the end of which the knocker is fastened.
=Bichromate of Potash.= A strong, yellowish-red chemical, used chiefly
in battery fluids and electrolytes.
=Bifilar Winding.= The method followed in winding resistance-coils. To
prevent them from creating fields of force, the wire is doubled and the
looped end started in the coil. Since the current passes in opposite
senses in the two lays of the winding, no field of force is produced.
=Binding.= Unattached wire wound round armature-coils to hold them in
place.
=Binding-post.= An arrangement for receiving the loose ends of wires in
an electric circuit and securing them, by means of screws, so that
perfect contact will be the result.
=Bi-polar.= Possessing two poles.
=Bi-telephone.= A pair of telephones arranged with a curved connecting
arm or spring so that they can be simultaneously applied to both ears.
=Blasting, Electric=. The ignition of a blasting charge of powder,
dynamite, or other high explosive by an electric spark, or by the
heating, to red or white heat, of a thin wire imbedded in the explosive.
=Block System.= A system of signalling on railroads. Signal-posts are
arranged at stated spaces, and on these signals appear automatically,
showing the location of trains to the engineers of trains in the rear.
=Bluestone.= A trade name for sulphate of copper in a crystallized
state.
=Bobbin.= A spool of wood or other non-conducting substance wound with
insulated wire. In a tangent galvanometer the bobbin becomes a ring with
a channel to receive the wire.
=Boiling.= In secondary, or storage, batteries the escaping of hydrogen
and oxygen gases, when the battery is fully charged, resembles water
boiling.
=Bonded Rails.= Rails used in an electric traction system, and which are
linked or connected together to form a perfect circuit. Used principally
in the third-rail system.
=Brake, Electro-magnetic.= A brake to stop the wheels of a moving car.
It consists of a shoe, or ring, which by magnetic force is drawn against
a rotating wheel to stop its revolution.
=Branch.= A conductor which leads off from a main line to distribute
current locally.
=Brassing.= A process of electro-depositing brass in a bath containing
both copper and zinc. A plate of brass is used as an anode.
=Brazing, Electric.= A process in which the spelter is melted by
electric current, so that the two parts are united as one.
=Break.= A point where an electric conductor is broken, as by a switch
or a cut-out.
=Bridge.= A special bar of copper connecting the dynamos with the bus
wire in electric lighting or power stations.
=Bronzing.= The deposition of bronze by electro-plating methods. The
mixture is of copper and tin, and a cast bronze plate is used as an
anode.
=Brush.= A term applied to the pieces of copper, carbon, or other
conducting medium in dynamos and motors, that bear against the
cylindrical surface of the commutators to collect or feed in the
current.
=Bug.= Any fault or trouble in the connections or workings of an
electrical apparatus. The term originated in quadruplex telegraphy, and
probably had some connection with the Edison bug-killer that he invented
when a boy.
=Buoy, Electric.= A buoy to indicate dangerous channels in harbors and
to mark wrecks and reefs. It is provided with an electric light at
night, and with a gong or an electric horn by day.
=Burner, Electric.= A gas-burner so arranged that the flame may be
lighted by electricity operated by a push-button at some distance from
the fixture, or, close at hand, by means of a chain or pull-string.
=Burning.= In a dynamo, the improper contact of brushes and commutator,
whereby a spark is produced and an arc formed which generates heat and
causes the metal parts to burn.
=Bus-rod.= A copper conductor used in power-plants to receive the
current from the battery of dynamos. The distributing leads are
connected to these rods.
=Butt-joint.= A joint made by bringing the ends of wires together so
that the ends butt. They are then soldered or brazed.
=Button, Electric.= A form of switch that is operated by pushing a
button mounted on a suitable base. Used principally for ringing bells,
operating lights, etc.
=Buzzer.= An electric alarm, or call, produced by the rapid vibration of
an armature acted upon by electro-magnetism. The sound is magnified by
enclosing the mechanism in a resonant box.
An apparatus resembling an electric bell _minus_ the bell and clapper.
The buzzer is used in places where the loud ring of a bell would be a
nuisance.
C
=C.= An abbreviation for centigrade when speaking of thermal
temperature. In chemistry the centigrade scale is used extensively, but
in air temperatures the Fahrenheit scale is universally employed.
=Cable, Aerial.= A cable that contains a number of wires separately
insulated, the entire mass being protected by an external insulation. It
is suspended in the air from pole to pole, and sometimes its weight is
so great that a supporting wire is carried along with it (usually
overhead), the large cable being suspended from it by cable-hangers.
=Cable Box=. A box to receive cable ends and protect them; also, the box
in which cable ends and line-wires are joined. Submarine cable boxes are
usually near the ground, while telephone and telegraph cable boxes are
mounted on poles, the cables running from the ground and up the poles to
the boxes.
=Cable-core.= The conductors of a cable which make up its interior
mass. For the convenience of linemen the wires are often insulated with
different-colored materials so that testing is not necessary when making
connections.
=Cable-hanger.= A metallic grip, usually of sheet metal, arranged to
clasp two or more wires. It is fastened to the supporting wire by a hook
and eye, or by small bolts with thumb-nuts.
=Cable-head.= A rectangular board equipped with binding-posts and fuse
wires so that the connections may be made between the cable ends and the
overhead or line-wires of a system.
=Cables.= An insulated electric conductor of large diameter, often
protected by armor or metallic sheathing, and generally containing, or
made up, of several separately insulated wires. Cables supply current to
traction lines; power, through subterranean passages; communication, by
submarine connection; and light, by overhead or underground conduits.
=Call-bell.= A bell that is rung by pressing a button, and which is
operated by electricity.
=Calling-drop.= A drop-shutter which is worked by electricity in a
telegraph or telephone exchange; it denotes the location from which the
call was sent in. Small red incandescent lamps have taken the place of
the drops in most of the large telephone exchanges, for they are
noiseless and do not annoy the operators as the drops and buzzers did.
=Candle-power.= The amount of light given by the standard candle. The
legal English and American standard is a sperm candle burning two grains
a minute.
=Candle, Standard.= The standard of illuminating power; a flame which
consumes two grains of sperm wax per minute, and produces a light of a
brightness equal to one candle-power.
=Caoutchouc.= India-rubber. So named because originally its chief use
was to erase or rub off pencil marks. It is a substance existing, in a
thick fluid state, in the sap or juices of certain tropical trees and
vines; it possesses a very high value as an insulator for wire and
circuits. The unworked, crude rubber is called virgin gum, but after it
is kneaded it is called masticated or pure gum rubber.
=Capacity.= A term used when speaking of the carrying power of a wire or
circuit. The capacity of a wire, rod, bar, or other conductor is
sufficient so long as the current does not heat it. Directly electric
heat is generated, we speak of the conductor as being overloaded or
having its capacity overtaxed.
=Capacity of a Telegraph Conductor.= The electric capacity may be
identical in quality with that of any other conductor. In quantity it
varies not only in different wires, but for the same wire under
different conditions. A 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. A wire placed near the
earth has greater capacity than one strung upon high poles, although the
wires may be of identical length and size and of the same metal. The
effect of high capacity is to retard the transmission of current, the
low capacity facilitates transmission.
=Capacity, Storage.= In secondary batteries, the quantity of electric
current they can supply, when fully charged, without exhaustion. This
capacity is measured or reckoned in ampere-hours.
=Carbon.= One of the elements in graphitic form used as an
electric-current conductor. It is the only substance which conducts
electricity, and which cannot be melted with comparative ease by
increase of current. It exists in three modifications--charcoal,
graphite, and the diamond. In its graphitic form it is used as an
electro-current conductor, as in batteries and arc-light electrodes, and
as filaments in incandescent lamps. In arc-lamp use the carbons are
usually electro-plated on the outside with a film of copper which acts
as a better conductor.
=Carbon, Artificial.= Carbon-dust, powdered coke, or gas carbon is mixed
with molasses, coal-tar, syrup, or some similar carbonaceous fluid, so
that the mass is plastic. It can then be moulded or pressed into shapes,
and heated to full redness for several hours by artificial or electric
heat. For lamp-carbons the mixture is forced through a round die by
heavy pressure, and is cut into suitable lengths, then fired or baked.
After removing and cooling, the carbons are sometimes dipped again into
the fluid used for cementing the original mass and re-ignited. This
process is termed “nourishing.” All carbon is a resisting medium, but at
high temperature the resistance is only about one-third as great; that
is, the current will pass through a red-hot carbon three times better
than through the cold carbon; or a current of thirty amperes will be
conducted as easily through a hot carbon as ten amperes through a cold
one.
=Carbon-cored.= A carbon for arc-lamps, the core being of softer carbon
than the outer surface. It is supposed to give a steadier light, and
fixes the position of the arc.
=Carbon-dioxide.= A compound gas, or carbonic-acid gas. It is a
dielectric.
=Carbon-holders.= In arc-lamps, the clamps arranged to hold the
carbon-pencils.
=Carbonization.= The ignition of an organic substance in a closed
vessel, so as to expel all constituents from it except the carbon.
A destructive distillation.
=Carbon Resistance.= (_See_ Resistance, Carbon.)
=Carbon Volatilization.= In arc-lamps the heat is so intense that it is
believed a part of the carbon-pencil is volatilized, as vapor, before
being burned or oxidized by the oxygen of the air.
=Carbons, Bare=. (_See_ Bare Carbons.)
=Carrying Capacity.= In a current-conductor, its carrying capacity up to
the heating-point. It is expressed in amperes.
=Cascade.= The arrangement of a series of Leyden-jars in properly
insulated stools, or supports, for accumulating frictional electricity.
They are arranged in a manner somewhat similar to a battery of galvanic
cells, the inner coating of one being connected to the outer coating of
the next, and so on through the series.
=Case-hardening, Electric.= A process by which the surface of iron is
converted into steel by applying a proper carbonaceous material to it
while it is being heated by an electric current.
=Cautery, Electric.= An electro-surgical appliance for removing diseased
parts or arresting hemorrhages. It takes the place of the knife or other
cutting instrument. It is a loop of platinum wire heated to whiteness by
an electric current.
=C.C.= An abbreviation commonly used for cubic-centimeter. It is usually
written in small letters, as 50 c.c., meaning 50 cubic-centimeters.
=Cell, Electrolytic.= A vessel containing the electrolyte used for
electro-plating.
=Cell, Regenerated.= A cell restored to its proper functions by a
process of recharging.
=Cell, Standard.= Meaning the same as battery. The vessel, including its
contents, in which electricity is generated.
=Cell, Storage.= Two plates of metal, or compounds of metal, whose
chemical relations are changed by the passage of an electric current
from one plate to the other through an electrolyte in which they are
immersed.
=Cements, Electrical.= Cements of a non-conducting nature, such as
marine glue and sticky compounds, used in electrical work.
=Centrifugal Force.= A diametric revolving force which throws a body
away from its axis of rotation. A merry-go-round is a simple example of
this force. The more rapidly the platform revolves the greater the
tendency for those on it to be thrown off and out from the centre. The
high velocity attained by the armatures in motors and dynamos would
throw the wires out of place and cause them to rub against the surfaces
of the field-magnets. Consequently, wire bands or binders are necessary
to keep the coils of wire from spreading under the influence of the
centrifugal force.
=Charge.= The quantity of electricity that is present on the surface of
a body or conductor.
The component chemical parts that are employed to excite the elements of
a cell in generating electric current.
=Charge, Residual.= After a Leyden-jar, or other condenser, has been
discharged by the ordinary methods, a second discharge (of less amount)
can be had after a few minutes’ waiting. This is due to what is known
as the residual charge, and is connected in some way with the molecular
distortion of the dielectric.
=Chemical Change.= When bodies unite so as to satisfy affinity, or to
bring about the freeing of thermal or other energy, the union is usually
accompanied by sensible heat or light. Sulphuric acid added to water
produces heat; a match in burning produces light. Another form of
chemical change is decomposition or separation (the reverse of
combination), such as takes place in the voltaic-battery, the
electro-plating bath, and other forms of electrolysis. This is not
accompanied by heat or light, but by the evolution of electricity.
=Chemical Element.= (_See_ Element, Chemical.)
=Chemistry.= The science which treats of the atomic and molecular
relations of the elements and their chemical compounds. Chemistry is
divided into many departments, but electro-chemistry treats only of the
science wherein electricity plays an active part, such as batteries,
electro-plating, and electro-metallurgy.
=Choking-coil.= (=See= Coil, Choking.)
=Circle, Magic.= A form of electro-magnet. It is a thick circle of round
iron used in connection with a magnetized coil to illustrate
electro-magnetic attraction.
=Circuit.= A conducting-path for electric currents. Properly speaking, a
complete circuit has the ends joined, and includes a source of current,
an apparatus, and other elements introduced in the path. When the
circuit is complete it is called active. The term circuit is also
applied to portions of a true circuit--as, an internal or external
circuit.
=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.
=Circuit-breaker.= Any apparatus for opening and closing a circuit, such
as switches, automatic cut-outs, lightning-arresters, and the like.
A ratchet-wheel engaged with a spring, or wire, which rests against the
teeth. The current passes through the wire, the wheel, and axle. The
wheel is revolved by a crank, and as the ratchets pass the spring, or
wire, an instantaneous make-and-break occurs. The speed of the wheel
regulates the frequency of the interruptions.
=Circuit, External.= A portion of the circuit not included within the
generator, such as a secondary telegraph key and sounder.
=Circuit, Grounded.= A circuit in which the ground is used as a
conductor. This is common in telegraph and telephone lines, particularly
for short distances where the conductivity of the earth does not offer
too much resistance.
=Circuit, Incandescent.= A circuit in which incandescent lamps are
installed.
=Circuit Indicator.= A pocket-compass, galvanometer, or other device for
indicating or detecting the condition of a wire, whether it is active or
dead, and, if active, in which direction the current is flowing. It may
also give a general idea of its strength.
=Circuit, Internal.= That portion of an electric circuit which is
included within the generator.
=Circuit Loop.= A minor circuit introduced, in series, into another
circuit by a switch or cut-out, so that it becomes a part of the main
circuit.
=Circuit, Main.= a circuit or main line, includes the apparatus
supplying current to it. Thus distinguished from a local circuit.
=Circuit, Metallic.= A circuit in which the current outside the
generator passes through metal parts or wire, but not through the
ground. Electric light and power lines are always metallic circuits. An
electro-plating apparatus may be properly termed a metallic circuit,
although a part of the circuit is formed by the electrolyte in the bath.
The essential meaning of the words metallic circuit is that the earth
does not form a part of the return circuit.
=Circuit, Open.= A circuit in which a switch has been opened to prevent
the continuous flow of current, such as an electric-bell circuit, which
normally remains open, and which is active only when the push-button is
pressed, thereby closing the circuit and operating the bell. An
open-circuit battery is one that remains inactive when the circuit is
open.
=Circuit, Parallel.= A term signifying a multiple circuit.
=Circuit, Quadruple.= A single circuit capable of having four messages
transmitted over it simultaneously--two in one direction, and two in the
other.
=Circuit, Return.= In telegraphy the ground is used as the return
circuit. It is also that portion of a circuit which leads from an
apparatus back to the terminal of a dynamo or battery, usually the
negative wire.
=Circuit, Short.= A connection between two parts of a circuit, causing
the current to skip a great part of its appointed path. Short-circuits
prevent the proper working of any electrical apparatus.
=Circuit, Simple.= A circuit containing a single generator, the proper
wire for carrying the current, and a switch to operate it. An
electric-bell line, a single telegraph line, or a direct telephone line
are all simple circuits.
=Clamp.= A tool for grasping and holding the ends of wires while joining
them.
The appliance for holding the carbon-pencils in arc-lamps.
=Cleats.= Blocks of wood, porcelain, or other insulating material used
to hold wires against a wall or beam. They have one, two, and three
notches at one side, for single, double, and three wire systems.
=Clutch, Electric.= A form of magnetic brake applied to car-wheels, the
armatures of motors, and other revolving mechanism, whereby the current,
passing through a coil, magnetizes a mass of cast-iron, and brings it to
bear frictionally upon the moving parts of the mechanism.
=Code, Cipher.= A set of disconnected words which, in accordance with a
prearranged key, stand for whole sentences and phrases. Commercially the
system is used as a short-cut--ten words perhaps meaning what otherwise
it would take forty or fifty words to express. It is used extensively in
telegraphy, both as an abbreviated message and as a means for securing
secrecy.
=Coherer.= Conducting particles constituting a semi-conducting bridge
between two electrodes, and serving to detect electro-magnetic waves.
The coherer in wireless telegraphy is understood to mean that form of
radio-receiver which, being normally at high resistance, is, under the
influence of Hertzian-waves, changed to a low resistance, thus becoming
relatively a conductor. Tubes of various kinds have been used for this
purpose. Within them is a filling of carbon granules, copper filings,
nickel and silver filings, and other substances. Marconi’s coherer
consists of a tube one and one-half inches long and one-twelfth inch
internal diameter. This is filled with filings--90 per cent. of nickel,
10 per cent. of silver. A globule of mercury coats the outer surface of
each grain with a thin film of the quicksilver. Into both ends a piece
of pure silver wire is plugged. These latter are a quarter of an inch
long, and fit the tube very accurately. The tube is thus sealed, and it
is considered preferable to have a slight vacuum within it.
=Coil.= A strand of wire wound in circular form about a spool, a
soft-iron core, or in layers, as a coil of rope.
An electro-magnetic generator.
A helix. (_See also_ Induction, Resistance, Magnetizing.)
=Coil, Choking.= A form of resistance to regulate the flow of current.
Any coil of insulated wire wound upon a laminated or divided iron core
forms a choking-coil. In alternating-current work special choking-coils
are used. They have a movable iron core, and by thrusting it in or out
the power is increased or diminished, thus raising or lowering the
lights, the same as gas is regulated.
=Coil, Faradic.= The name given to a medical induction-coil or faradic
machine.
=Coil, Induction.= A coil in which the electro-motive force of a portion
of a circuit is, by induction, made to produce higher or lower
electro-motive forces in an adjacent circuit, or in a circuit a part of
which adjoins the original circuit. There are three principal parts to
all induction-coils--the core, the primary coil, and the secondary coil.
The core is a mass of soft iron, cast or wrought, but preferably
divided--for example, a bundle of rods or bars. The primary coil of
comparatively larger wire is wound about this core, each layer being
properly insulated and varnished, or coated with melted paraffine, to
bind the wires. The secondary coil is of fine wire, and is wound about
the primary coil. A great many turns of the fine wire are necessary, and
care must be taken to properly insulate each layer and shellac the
wires. The primary must be well insulated from the secondary coil, so as
to prevent sparking, which would destroy the insulation. A
make-and-break is operated by the primary coil, and is constructed upon
the general form of an electric bell or buzzer movement. Extra currents
which interfere with the action of an induction-coil are avoided by the
use of a condenser. (_See also_ Condenser.) The induction-coil produces
a rapid succession of sparks which may spring across a gap of thirty or
forty inches, according to the size of the coil. Induction-coils are
used extensively in electric work, especially in telephone transmitters,
wireless telegraphy, electric welding, and in the alternating-current
system.
=Coil, Magnetizing.= A coil of insulated wire so wound that a well or
aperture will be formed. Within this well a piece of steel is placed, so
that an electric current, passing through the wires, will magnetize the
steel; or a steel rod may be passed in and out of the hole several times
while a strong current is travelling through the coil, thus magnetizing
the rod.
=Coil, Resistance.= A coil so constructed that it will offer resistance
to a steady current of too great electro-motive force for the safety of
the apparatus. Generally the coil is made by doubling the wire without
breaking it, then starting at the doubled end to wind it in coil or
spring fashion. If the wire is too heavy to wind double, a single strand
is wound on a square or triangular insulator in which notches are made.
Then, alternately between the coils, the second strand is wound. The
strands are joined at one end of the coil, but those at the other are
left free for unions with other wires. (_See also_ Resistance.)
=Coil, Retarding.= A choking-coil. A resistance-coil.
=Coil, Ribbon.= Instead of wire, flat, thin strips of sheet-metal are
sometimes used for resistance-coils, doubled, as explained above. The
wraps are insulated with sheet-mica, micanite, or asbestos, to prevent
short-circuiting.
=Coil, Ruhmkorff.= A common type of induction-coil with a vibrator or
circuit-breaker. Used with constant and direct current.
A step-up transformer with a circuit-breaker attachment.
=Coils, Idle.= Coils in a dynamo in which no electro-motive force is
being generated or developed.
Coils that, through broken connections or short circuits, are inactive.
=Column, Electric.= An old name for the voltaic pile. The apparatus made
up of a pile of disks of copper and zinc, separated by pieces of flannel
wet with acidulated water.
=Comb.= 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 electric machine.
=Commutator.= An apparatus used on motors and dynamos and
induction-coils for changing the direction of currents. It is made in a
variety of types, but usually in the shape of insulated bars closely
packed about an armature shaft.
=Commutator-bars.= The metallic segments of a dynamo or
motor-commutator.
=Commutators, Quiet.= Commutators that do not spark during the
revolutions of the armature.
=Compass.= An apparatus for indicating the directive force of the earth
upon the magnetic needle. It consists of a case covered with glass, in
which a magnetized needle, normally pointing to the north, is balanced
on a point at the centre. Under the needle a card is arranged on which
the degrees or points of the compass are inscribed. A valuable
instrument in electrical work, magnetism, etc.
=Compass, Liquid.= A form of marine compass. The needle is attached to a
card or disk which floats in alcohol or other spirits, so as to check
undue oscillation.
=Compass, Mariners’.= A compass in which the needle is attached to a
card that rotates in pointing to the north. A mark, called the “lubber’s
mark,” is made upon the case, and this is in line with the ship’s keel,
so that a glance at the card will indicate the direction in which the
ship is headed.
=Compass, Spirit.= A form of mariners’ compass in which the bowl, or
case, is sealed and filled with alcohol. The compass-card works as a
spindle, and, by a series of air compartments, floats on the alcohol.
The friction of the pivot is thereby greatly diminished, making the
compass a very sensitive one.
=Compass, Standard.= A compass employed as a standard by which to
compare other compasses.
=Condenser.= An appliance for storing up electro-static charges; it is
also called a static accumulator. The telegraphic condenser consists of
a box packed full of sheets of tin-foil having a sheet of paraffined
paper or sheet-mica between every two sheets. The alternate sheets of
tin-foil are connected together, and each set has its binding-post.
(_See also_ Electrostatic Accumulator.)
=Condenser, Air.= (_See_ Air-condenser.)
=Condenser, Ayrton’s.= (_See_ Ayrton’s Condenser.)
=Condenser-plate.= (_See_ Plate, Condenser.)
=Condenser, Sliding.= An apparatus in the form of a Leyden-jar whose
coatings can be slid past each other to diminish or increase the face
area, and also to diminish or increase the capacity of the condenser.
=Conductance.= The conducting power of a mass of material, varying
according to its shape and dimensions. The cylindrical or round
conductor is the best type for the conveyance of electric currents.
=Conduction.= The transmission of electricity through an immobile
medium, such as a wire, or rod, or a bar.
=Conductivity.= Ability to conduct electric currents. The conductivity
of a wire is its power to conduct or transmit a current. Glass has no
conductivity, and it is therefore a non-conductor.
=Conductivity, Variable.= The change in the conducting or transmitting
powers of metals and substances under different temperatures. Hot metal
conducts an electric current better than cold. A hot carbon-pencil in an
arc-light conducts the current better than when the light is first
started, for as it warms up under the influence of the arc-flame the
current passes more freely. Five minutes after the current is turned on
the lamps in the circuit give a steady light, and do not sputter as when
they first start up.
=Conductor.= Anything which permits the passage of electric current. The
term conductor is a relative one, and, excepting a vacuum, there is
probably no substance that has not some conductive power. Metals,
beginning with silver, are the best conductors, liquids next, glass the
worst. The ether, or air, is a conductor of sound and electric vibratory
disturbances, but not in the same sense as the ground. The air conducts
frictional electricity, while the ground acts as a conductor for the
galvanic current, or “current electricity.” By this last term is meant
electricity which flows continually, instead of discharging all at once,
with an accompanying spark or flash.
=Conductor, Overhead.= Overhead electric lines, wires or cables, for
conducting current. Generally poles are erected for this purpose.
=Conductor, Prime.= A cylindrical or spherical body with no points or
angles, but rounded everywhere and generally of metal. If made of other
material, such as wood, glass, or composition, its entire surface is
rendered conductive by being covered with sheet-metal, such as tin-foil,
gold-leaf or tinsel, applied to it with paste, shellac, or glue. A prime
conductor should be mounted on an insulated stand; it is employed to
collect and retain frictional electricity generated by a static machine.
=Conductor, Underground.= An insulated conductor which is placed under
the surface of the earth, passing through conduits.
=Connect.= The act of bringing two ends of wire together, either
temporarily or permanently. Bringing one end of a conductor into contact
with another so as to establish an electric connection.
=Connector.= A sleeve, with screws or other clamping device, into which
the ends of wires or rods may be passed and held securely. A
binding-post and spring-jack comes under this head.
=Contact.= The electrical union of two conductors, whether temporary or
permanent. It may be established by touching the ends or terminals of a
circuit through the agency of a push-button, a telegraph-key, an
electric switch, etc.
=Contact-breaker.= (The same as Circuit-breaker, _which see_.)
=Contact, Loose.= A contact formed by two or several surfaces imposed
one upon another and held by their weight alone.
=Contact-point.= A point, or stud, often of silver or platinum, arranged
to come into touch with a contact-spring, such as the vibrating armature
of an electric bell.
=Contact-spring.= A spring connected at one end of a lead and arranged
to press against another spring or plate, so that a plug may be inserted
between the contact-points.
=Controller.= The lever or handle on the switch-board of a
resistance-coil, by means of which electric current is let in or kept
out of a circuit.
=Controlling Force.= In galvanometers and similar instruments, the force
used to bring the needle or indicator back to zero.
=Converter.= An induction-coil used with the alternating current for
changing the potential difference and inverting the available current.
High alternating voltage may be converted into lower direct-current
voltage, thereby increasing the amperage or current. A converter
consists of a core of thin iron sheets, wound with a primary coil of
fine insulated wire, with many convolutions or turns. Also, a secondary
coil made up of coarse insulated wire with fewer convolutions. The coil
may be jacketed with iron to increase the permanence.
=Converter, Rotary.= A combined motor and dynamo whose function is to
transform a current of high or low voltage (A-C., or D-C.) into any
other kind of current desired.
=Convolution.= The state of being convolved; a turn, wrap, fold, or
whorl. A clock-spring is a familiar example.
=Copper-bath.= A solution of sulphate of copper used in electro-plating,
electrotyping, and copper-refining by electricity.
=Cord, Flexible.= A flexible-wire conductor made up of many strands of
fine wire and properly insulated so that it may be easily twisted, bent,
or wrapped. Flexible wire is used as the conductors for portable
electric lights, push-buttons, medical coils, etc.
=Core.= The iron mass (generally located in the centre of a coil or
helix) which becomes highly magnetic when a current is flowing around
it, but which looses its magnetism immediately that the current ceases
to flow.
A conductor or the conductors of an electric cable made up of a single
strand or many strands laid together and twisted. These may be of bare
metal, or each one insulated from the others.
=Core-disks.= Disks of thin wire, for building up armature-cores. The
usual form of a core is round or cylindrical. A number of thin disks, or
laminations, of iron strung upon the central shaft, and pressed firmly
together by the end-nuts or keys. This arrangement gives a cylinder as a
base on which to wind the insulated wire that forms a part of the
armature.
=Core-disks, Pierced.= Core-disks for an armature of a motor or dynamo,
which have been pierced or bored out around the periphery. Tubes of
insulating material, such as fibre, rubber, or paraffined paper, are
inserted in the holes and through these the windings of wire are
carried. The coils are thus imbedded in the solid mass of iron, and are
protected from eddy currents; also they act to reduce the reluctance of
the air-gaps. This arrangement is very good, from a mechanical point of
view, but in practice its use is confined to small motors only, and
dynamos generating under one hundred volts.
=Core-disks, Toothed.= Core-disks of an armature or motor where notches
are cut from the periphery. When they are locked together, to form the
armature-core, the coils of wire lie in the grooves formed by a number
of the disks bound together. This construction reduces the actual
air-gaps and keeps the coils equally spaced.
=Core, Laminated.= The core of an armature, an induction-coil, a
converter, or any similar piece of apparatus, which is made up of plates
or disks, insulated more or less perfectly from one another by means of
mica or paraffined paper. The object of laminations is to prevent the
formation of Foucault currents. A core built up of disks is sometimes
called a radially laminated core.
=Core, Ring.= A dynamo or motor armature-core which forms a complete
ring.
=Core, Stranded.= The core of a cable, or a conducting core made up of a
number of separate wires or strands laid or twisted together.
=Core, Tubular.= Tubes used as cores for electro-magnets, and also to
produce 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 current, however, the tubular
core becomes less efficient.
=Coulomb.= The practical unit of electrical quantity. It is the quantity
passed by a current of one ampere intensity in one second.
=Couple.= The combination of two electrodes and a liquid, the
electrodes being immersed in the latter, and being acted on
differentially by the liquid. This combination constitutes a source of
electro-motive force, and, consequently of current, and is called the
galvanic or voltaic cell or battery.
=Couple, Astatic.=. A term sometimes applied to astatic needles when
working in pairs.
=Coupling.= The union of cells or generators constituting a battery; the
volume of current, or electro-motive force, is thereby increased.
=C. P.= An abbreviation for “candle power”; also meaning “chemically
pure,” when speaking of chemicals.
=Crater.= The depression that forms in the positive carbon of a
voltaic-arc.
=Creeping.= A phenomena met with in solution batteries. The electrolyte
creeps up the sides of the containing jar and evaporates, leaving a
deposit of salts. Still more solution creeps up through the salts until
it gets clear to the top and runs over. To prevent this the tops of the
jars should be brushed with hot paraffine for a distance of two inches
from the upper edge. The salts will not form on paraffine. Oil is
sometimes poured on the top of the battery solution, but this affects
the elements if it touches them, and makes their surfaces
non-conducting.
=Crucible, Electric.= A crucible for melting refractory substances, or
for reducing ores by means of the electric arc produced within it.
Probably the result obtained is due more to current incandescence than
to the action of the arc.
=Crystallization, Electric.= Under proper conditions many substances and
liquids take a crystalline form. When such action is brought about by
means of electricity the term electric crystallization may be applied
to the phenomenon. A solution of nitrate of silver, when decomposed by a
current, will give crystals of metallic silver. A solution of common
salt or brine, when electrically decomposed, will produce sodium and
chlorine. The sodium appears at the leading-out electrode and readily
unites with carbonic-acid gas, which is injected into the apparatus. The
result of the combination is carbonate of soda, one of the most
important products of the alkali industry.
=Current, Alternating.= A current flowing alternately in opposite
directions. It is a succession of currents, each of short duration and
of direction opposite to that of its predecessor. Abbreviation, A-C.
=Current, Amperage.= The volume of electricity passing through any
circuit per second, the flow being uniform.
=Current, Constant.= An unvarying current. A constant-current system is
one in which the current is uniformly maintained--for example, in
electric light, power, and heat plants.
=Current, Continuous.= A current of one direction only, or the reverse
of an alternating current.
=Current, Direct.= A current of unvarying direction, as distinguished
from the alternating. Abbreviation, D-C.
=Current Distribution, Uniform.= A steady current; a current whose
density in a conductor is always the same at all points.
=Current, Induced.= A current caused by electro-dynamic induction.
=Current, Low Potential.= A current of low pressure.
A term applied to low electro-motive force.
=Current, Make-and-break.= A current which is continually broken or
interrupted and started again. The term is applied only where the
interruptions occur in rapid succession, as in the action of an
induction-coil or pole-changer.
The alternating current.
=Current-meter.= An apparatus for indicating the strength of a current,
such as an ammeter.
=Current, Oscillating.= A current periodically alternating.
=Current, Periodic.= A current with periodically varying strength or
direction. A current alternating periodically.
=Current, Polarizing.= A current which causes polarization.
=Current-reverser.= A switch or other contrivance for reversing the
direction of a current in a conductor.
=Current, Undulating.= A current whose direction is constant but whose
strength is continuously varying.
=Currents, Eddy.= Useless currents in an armature, in the pole pieces,
and in the magnetic cores of dynamos and motors. They are created by the
high speed of the armature in its rotation, or by other electric
currents induced by the armature’s motion through magnetic fields.
=Currents, Faradic.= Induced currents. They take their name from Michael
Faraday, the original investigator of the phenomena of electro-magnetic
induction. The secondary or induced electro-magnetic currents and their
accompanying phenomena.
A series of alternating electro-static discharges from influence
machine, such as the Holtz and Wimshurst.
The simple and commonly understood Faradic currents are those produced
in the medical battery, and used in medical therapeutics.
=Currents, Foucault.= A form of currents produced in revolving
armature-cores; sometimes called eddy currents. They are useless.
=Currents, Harmonic.= Currents which alternate periodically, and vary
harmonically. Currents which vibrate at certain pitches, as, for
instance, the currents in wireless telegraphy. Two instruments must be
tuned to the same pitch in order to be responsive. Thus an instrument
sending out waves of 70,000 vibrations cannot be recorded by one tuned
much below or above the same number.
Sound waves of sympathetic or harmonic vibrations.
=Currents, Positive.= (_See_ Positive Currents.)
=Cut-in.= To electrically connect a piece of mechanism or a conductor
with a circuit.
=Cut-out.= The reverse of the cut-in. To remove from a circuit any
conducting device. The cut-out may be so arranged as to leave the
circuit complete in some other way.
An appliance for removing a piece of apparatus from a circuit so that no
more current shall pass through the former.
=Cut-out, Automatic.= A safety device for automatically cutting out a
circuit to prevent accident or the burning-out of an apparatus, due to
an overload of current. It is worked by an electro-magnet and spring. An
overload of current causes a magnet of high resistance to draw an
armature towards it, and this, in turn, releases the spring of the
cut-out device. Sometimes a strip or wire of fusible metal is employed
which is in circuit with a switch. The excess of current fuses the
metal, and the broken circuit releases a spring-jack, which, in turn,
breaks the circuit.
=Cut-out, Safety.= A block of non-conducting material, such as marble,
slate, or porcelain, carrying a safety-fuse or plugs. In these is
enclosed a piece of fusible wire, which burns out or melts and breaks
the circuit before the apparatus is damaged.
=Cut-out, Wedge.= A cut-out operated by a wedge, such as a spring-jack
or the plugs at the end of the flexible wires on the switch-boards of
telephone exchanges.
D
=Damper.= A frame of copper on which the wire in a galvanometer is
sometimes coiled. It acts to check the needle oscillations.
A brass or copper sheathing or tube placed between the primary and
secondary coils of an induction-coil to cut off induction and diminish
the current and potential of the secondary circuit. When the tube is
drawn out gradually the induction increases. It is commonly used in
medical coils to adjust their strength of action.
=D-C.= An abbreviation for direct current.
=Dead Earth.= A fault in telegraph and telephone lines which consists in
the ground-wire being improperly grounded, or not fully connected with
the earth.
=Dead Turns.= A term applied to the ten to twenty per cent. of the
convolutions or turns of wire on an armature which are considered to be
dead. There are supposed to be about eighty per cent. of the turns on an
armature that are active in magnetizing the core; the balance are
outside the magnetic field and are termed dead, although they are
necessary to the production of electro-motive force.
=Dead Wire.= A wire in the electric circuit through which no current is
passing.
A disused or abandoned electric conductor, such as a telegraph wire, or
a wire which may be in circuit, but through which at the time of
speaking no electrical action is taking place.
=Death, Electrical.= Death resulting from an electric current passing
through the animal body--electrocution; accidental death by electric
shock; premeditated death through bringing the body in direct contact
with conductors carrying high electro-motive force. High electro-motive
force is essential, and the alternating current is most fatal.
=Decomposition, Electrolytic.= The decomposition or separation of a
compound liquid into its constituents by electrolysis. The liquid must
be a conductor or electrolyte, and the decomposition is carried on by
means of electricity.
The conversion of two or more chemicals into a new compound or
substance.
=Deflection.= In magnetism, the movement of the needle out of the plane.
It is due to disturbance, or to the needle’s attraction towards a mass
of iron or steel or another magnet.
=Demagnetization.= The removal of magnetism from a paramagnetic
substance. The process is principally in use for watches which have
become magnetized by exposure to the magnetic field surrounding dynamos
or motors.
=Density, Electric.= The relative quantity of electricity, as a charge,
upon a unit area of surface. It may be positive or negative.
Surface density, as the charge of a Leyden-jar.
=Depolarization.= A term applied to the removal of permanent magnetism,
such as that from a horseshoe magnet, a watch, or a bar-magnet. Heat is
the common depolarizer, but counter electro-magnetic forces are employed
also in the various forms of apparatus known as demagnetizers.
=Deposit, Electrolytic.= The metal or other substances precipitated by
the action of a battery or other current-generator, as in the plating
processes.
=Detector.= A portable galvanometer, by means of which a current and its
approximate strength can be detected and measured.
=Diaphragm.= In telephones and microphones, a disk of iron thrown into
motion by sound-waves or by electric impulse. It is usually a thin plate
of japanned iron, such as is used in the ferrotype photographic process
for making tin-types.
=Dielectric.= Any substance through which electrostatic induction is
allowed to occur, such as glass or rubber. It is a non-conductor for all
electric currents.
=Dielectric Resistance.= The resistance a body offers to perforation or
destruction by an electric discharge.
=Dimmer.= An adjustable choke or resistance coil used for regulating the
intensity of electric incandescent lamps. It is employed extensively in
theatres for raising or lowering the brilliancy of lights.
=Dipping.= The process of cleaning articles by dipping them in acids or
caustic soda, preparatory to electro-plating.
Simple immersion, with or without current, to put a blush of metal on a
cleaned surface.
=Dipping-needle.= A magnetic needle mounted on a horizontal bearing so
that it will dip vertically when excited by a current passing
horizontally about it. The ordinary compass-needle is mounted on a
point, and swings freely to the right or left only.
=Direct Current.= (_See_ Current, Direct.)
=Discharge.= The eruptive discharge from a Leyden-jar or accumulator of
a volume of electricity stored within it.
The abstraction of a charge from a conductor by connecting it to the
earth or to another conductor.
=Discharge, Disruptive.= The discharge of a static charge through a
dielectric. It involves the mechanical perforation of the dielectric.
=Disconnect.= To break an electric circuit or open it so as to stop the
flow of current; to remove a part of a circuit or a piece of apparatus
from a circuit.
=Distillation, Electric.= The distilling of a liquid by the employment
of electricity, which, by electrifying the liquid, assists the effects
of heat. It is asserted that the process is accelerated by the
electrification of the liquid or fluid, but it must be a conductor
liquid or electrolyte. Oil, being a non-conductor, is not affected by
any electric current, no matter what its specific gravity may be.
=Distributing Centre.= The centre of distribution in a system having
branch circuits, such as the electric-light or telephone outlets from a
main station.
=Door-opener, Electric.= A magnetic contrivance arranged in connection
with a lock, by means of which the latch is released by pressing a
distant push-button. This device is used in flats and apartment-houses
for opening a door from any of the apartments in the house.
=Double Filament Lamp.= An incandescent lamp having two filaments, one
with a high capacity, the other with a low one. The high capacity may be
from sixteen to fifty candle-power, the other from one to five. A turn
of the bulb in its socket, or the pulling of a string which operates a
switch in the socket, cuts out the current from the long filament and
sends it through the shorter and finer one, thus giving a weaker light.
These “hy-lo” lamps are useful as night lamps in halls, bath-rooms, or
in sick-rooms, where a low or weak light is required all night.
=Double Pole-switch=. A cut-out that is arranged to cut out the circuit
of both the negative and positive leads at the same time.
=Double-push.= A contact-push having two contacts and arranged so that
pressure upon it opens one contact and closes the other.
=Double Throw-switch.= A switch so arranged that it can be thrown into
either one of two contacts; a throw-over switch.
=Driving-pulley.= The broad-faced or channelled pulley on an armature
shaft by means of which the power from a motor may be transmitted
mechanically.
=Dry Battery.= (_See_ Battery, Dry.)
=Duct.= The space in an underground conduit for a single wire or cable.
=Duplex Wire.= An insulated conductor having two distinct wires twisted
or laid together, but properly insulated from each other.
=Dynamic Electricity.= Electricity in motion or flowing, as
distinguished from static or frictional electricity.
Electricity of relatively low potential or electro-motive force in large
quantity or amperage.
=Dynamo.= An apparatus consisting of a core and field-magnets, properly
wound with insulated wire, which, when put into operation by revolving
the core or armature at high speed, develops electric current; a
mechanical generator of electricity.
=Dynamo, Motor.= (_See_ Motor-dynamo.)
E
=Earth.= The accidental grounding of a circuit is termed an “earth.”
=Earth-plate.= A plate buried in the ground to receive the ends of
telegraph lines and other circuits, and so give a ground connection.
Copper plates are often used, but in houses the ground is usually formed
by attaching a wire to the gas or water pipes.
=Earth Return.= The grounding of a wire in a circuit at both ends gives
the circuit an earth return. This method is commonly used in telegraph
lines, both in the wire and wireless systems.
=Eddy Currents.= (_See_ Currents, Eddy.)
=Edison Distributing-box.= A box used in the Edison “three-wire” system,
from which the outlets pass to local circuits.
=Edison Lalande Cell.= A zinc-copper battery having a depolarizing
coating of copper oxide on the copper element, the couple being immersed
in an electrolyte composed of potash or caustic soda.
=Ediswan.= A term applied to the incandescent lamps invented by Edison
and Swan and used extensively in Great Britain. Also applied to other
apparatus designed by the two inventors.
=Efficiency.= The relation of work done to the electrical energy
absorbed. The efficiency is not equal to the energy absorbed, because it
always takes more power to generate a current than is given back in
actual efficiency. This is due to mechanical friction and to the
resistance of the air in a mechanism such as a dynamo when revolving at
high speed.
=Efficiency, Electrical.= In a generator it is the total electrical
energy produced, both that wasted and that actually used in driving
machinery or apparatus.
=Efflorescence.= The dry salts on a jar or vessel containing liquid
that collects above the water or evaporation line. This is due to
creeping.
=Elasticity.= A property in some bodies and forces through which they
recover their former figure, shape, or dimensions when the external
pressure or stress is removed. Water has no elasticity. Air is very
elastic; steam has a great volume of elasticity; while electricity is
undoubtedly the most elastic of all in its motion through air, water,
and other conducting mediums.
=Electric.= Pertaining to electricity; anything connected with the use
of electricity. It has been a much-abused word, and its meaning has been
garbled by the impostor, the crook, and the “business thief” in foisting
on the public wares in which there was no electrical property whatever.
“Electric” toothbrushes, combs, corsets, belts, and the like may contain
a few bits of magnetized steel, but they possess no active therapeutic
value.
=Electrical Engineer.= The profession of electrical engineer calls for
the highest knowledge of electricity, both theoretical and practical. It
embraces the designing and installation of all kinds of electrical
apparatus.
=Electrician.= One versed in the practices and science of electricity; a
practical lineman or wireman.