Chapter XV

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.

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.

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.

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.

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.

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.

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.

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.

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.”

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.

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.

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.

=Electricity.= One of the hidden and mysterious powers of nature, which man has brought under control to serve his ends, and which manifests itself mainly through attraction and repulsion; the most powerful and yet the most docile force known to man, coming from nowhere and without form, weight, or color, invisible and inaudible; an energy which fills the universe and which is the active principle in heat, light, magnetism, chemical affinity, and mechanical motion.

=Electricity, Atmospheric.= The electric currents of the atmosphere, variable but never absent. They include lightning, frictional electricity, the Aurora Borealis, the electric waves used in wireless telegraphy, etc. Benjamin Franklin indicated the method of drawing electricity from the clouds. In June, 1752, he flew a kite, and by its moistened cord drew an electric current from the clouds so that sparks were visible on a brass key at the ground end of the cord. Later, when a fine wire was substituted for the cord, and a kite was flown in a thunder-storm, the electric spark was vivid. This experiment confirmed his hypothesis that lightning was identical with the disruptive discharges of electricity.

=Electricity, Latent.= The bound charge of static electricity.

=Electricity, Negative.= (_See_ Negative Electricity.)

=Electricity, Positive.= (_See_ Positive Electricity.)

=Electricity, Voltaic.= Electricity of low potential difference and large current intensity.

Electricity produced by a voltaic battery or dynamo as opposed to static electricity, which is frictional and practically uncontrollable for commercial purposes.

=Electrification.= The process of imparting an electric charge to a surface. The term is applied chiefly to electro-static phenomena.

=Electrization.= In electro-therapeutics, the subjection of the human system to electric treatment. An electric tonic imparted by electro-medical baths through the nervous system.

=Electro-chemistry.= That branch of science which treats of the relations between electric and chemical forces in their different reactions and compounds. It deals with electro-plating, electro-fusing, electrolysis, etc.

=Electro-culture.= The application of electricity to the cultivation of plants. The use of electricity has been found very beneficial in some forms of plant growth.

=Electrocution.= Capital punishment inflicted by electric current from a dynamo of high electro-motive force. The current used is from 1500 to 2000 volts, and it acts to break down the tissues of the body.

=Electrode.= The terminals of an open electric circuit.

The terminals between which an electric arc is formed, as in the arc-light.

The terminals of the conductors of an electric circuit immersed in an electrolytic solution, such as the carbon and zinc of a battery.

=Electrolier.= A fixture for supporting electric lamps, similar to a chandelier for gas or candles. Combination electroliers conduct both gas and electricity.

=Electrolysis.= The separation of a chemical compound into its constituted parts by the action of an electric current.

=Electrolyte.= A body susceptible of decomposition by the electric current. It must be a fluid body and a conductor capable of diffusion as well as composite in its make-up. An elemental body such as pure water cannot be an electrolyte.

=Electrolytic Decomposition.= (_See_ Decomposition, Electrolytic.)

=Electrolytic Deposit.= (_See_ Deposit, Electrolytic.)

=Electrolytic Resistance.= (_See_ Resistance, Electrolytic.)

=Electro-magnetic Induction.= (_See_ Induction, Electro-Magnetic.)

=Electro-magnetism.= Magnetism created by electric current.

That branch of electrical science which treats of the magnetic relations of a field of force produced by a current.

=Electro-medical Bath.= A bath provided with connections and electrodes for causing a current of electricity to pass through the body of the patient.

=Electrometer.= An instrument used for measuring static electricity. Electrometers are different from galvanometers, since the latter depend on a current flowing through wires to create an action of the magnetic needles.

=Electro-motive Force.= Voltage. It may be compared to the pressure of water in hydraulic systems. The unit of electro-motive force is the volt.

=Electro-motor.= A term sometimes applied to a current-generator, such as a small dynamo or voltaic battery.

=Electro-plating.= (_See_ Plating, Electro.)

=Electropoion Fluid.= An acid depolarizing solution for use in zinc-carbon couples, such as the “Grenet” and “Daniell” cells. The bi-chromate-of-potash and sulphuric-acid solution for battery charges is a good example.

=Electroscope.= An apparatus for indicating the presence of an electric charge and whether the charge is negative or positive.

=Electrostatic Accumulator.= Two conducting surfaces, separated by a dielectric and arranged for the opposite charging of the two surfaces. A faradic or static machine for accumulating frictional electricity is an example.

=Electrostatics.= That division of electric science which treats of the phenomena of the electric charge, or of electricity in repose, as contrasted with electro-dynamics or electricity in motion.

=Electrotype.= The reproduction of a form of type or engraving by the copper electro-plating process. The original is coated with plumbago and a wax impression taken of it. The face of the negative is made conductive with plumbago or tin dust, then suspended in a copper bath and connected with the current. A film of copper will be deposited on the face of the wax impression.

=Element, Chemical.= Original forms of matter that cannot be separated into simple constituents by any known process. There are about seventy in all, but as science advances the list is constantly being revised. New elements are discovered and known ones are being resolved into simpler forms.

=Elements of Battery Cell.= (_See_ Battery Cell, Elements of.)

=Emergency Switch.= An auxiliary switch used as a controller on a car to reverse the action of the motor.

=E-M-F.= An abbreviation for electro-motive force, or voltage.

=Equalizer.= A term applied to a wire or bar in electro-magnetic mechanism for equalizing the pressure over a system.

=Exciter.= A generator used for exciting the field-magnets of a dynamo.

=Extension Call-bell.= A bell connected with a telephone call-bell, and located in another part of a building so as to give a distant summons.

=External Circuit.= (_See_ Circuit, External.)

F

=F.= The sign commonly employed to designate Fahrenheit. Thus, 30° F. means 30 degrees Fahrenheit, or 30 degrees above zero.

=False Magnetic Poles.= (_See_ Magnetic Poles, False.)

=Faradic.= Induced current produced from induction-coils and faradic machines.

A series of alternating electrostatic discharges, as from a Holtz influence machine.

=Faradic Coil.= (_See_ Coil, Faradic.)

=Faradic Currents.= (_See_ Currents, Faradic.)

=Faradic Machine.= An apparatus designed to produce faradic current.

=Feed.= To furnish an electric current, also spoken of in connection with the mechanism that moves the carbons in arc-lamps.

=Feeders, or Feed Wires.= The conductors which convey electric currents at different points, as in the trolley system. The current is carried along in large cables strung on poles or laid underground, and at proper distances lines are run in to feed the trolley wire.

=Field.= The space in the neighborhood of a dynamo or motor, or other generator of electric current, from which the apparatus takes its electricity, both electrostatic and magnetic.

=Field-magnet.= (_See_ Magnet, Field.)

=Field of Force.= The space in the neighborhood of an attracting or repelling mass or system. There are two kinds of fields of force--the electro-magnetic and the static--from which the respective pieces of apparatus draw their store of electricity.

=Filament.= A long, thin piece of solid substance. It is generally as thin as a thread and flexible enough to be bent.

The hairlike element in an incandescent lamp which, when heated by a current, glows and radiates light.

=Filaments, Paper.= Filaments for incandescent lamps made of carbonized paper. They were the ones originally used in electric lamps, but have been superseded by other substances easier to handle and more durable.

=Flow.= The volume of a current or stream escaping through a conductor, such as a wire, rod or pipe.

=Fluorescence.= The property of converting ether waves of one length into waves of another length. The phenomenon is utilized in the production of Geissler tubes and X-rays.

=Fluoroscope.= An apparatus for making examinations by means of the X-rays.

=Fluoroscopic Screen.= A screen overspread with fluorescent material and employed for fluoroscopic examinations in connection with the X-rays.

=Force.= Any change in the condition of matter with respect to motion or rest. Force is measured by the acceleration or change of motion that it can impart to a body of a unit mass in a unit of time. For instance, ten pounds pressure of steam will be indicated on a gauge made for measuring steam. That pressure of steam, with the proper volume behind it, is capable of instantly producing a given part of a horse-power. In the same way ten volts of electro-motive force is capable of pushing a current so as to exert a certain fraction of horse-power.

=Force, Electro-magnetic.= The force of attraction or repulsion exerted by the electro-magnet. It is also known as electric force in the electro-magnetic system.

=Foucault Currents.= (_See_ Currents, Foucault.)

=Fractional Distillation.= The process of evaporating liquids by heat, the most volatile being the first treated. When that has been evaporated and distilled the heat is raised and the next most volatile liquid is evaporated, and so on until all are evaporated, leaving as a residue the solids that were a part of the original mass of liquid.

=Friction.= The effect of rubbing, or the resistance which a moving body encounters when in contact with another body.

=Frictional Electric Machine.= An apparatus for the development or generation of high-tension frictional electricity.

=Frictional Electricity.= Electricity produced by the friction of dissimilar substances.

=Full Load.= A complete load. The greatest load a machine or secondary battery will carry permanently. The full capacity of a motor running at its registered speed for its horse-power.

=Furnace, Electric.= A furnace in which the heat is produced by the electric arc. It is the hottest furnace known to man, and temperatures as high as 7500° Fahrenheit have been developed in it.

=Fuse, Electric.= A fuse for igniting an explosive charge by electricity. It is made by bringing the terminals or ends of wires close together, so that they will spark when a current passes through them. Or a thin piece of highly resistant wire may be imbedded in an explosive and brought to white heat by current.

=Fuse-block.= An insulator having a safety-fuse made fast to it.

=Fuse-box.= A box containing a safety-fuse, generally of porcelain, enamelled iron, or some other non-conductor.

=Fuse-links.= Links composed of strips or plates of fusible metal serving the purpose of safety-fuses.

=Fusing-current.= A current of sufficient strength to cause the blowing or fusing of a metal.

G

=Galvanic.= Voltaic. Relating to current electricity or the electro-chemical relations of metals.

=Galvanic Taste.= A salty taste in the mouth resulting from the passage of a light current from a voltaic battery, the ends of the wires being held to either side of the tongue. This has been called tasting electricity, but it is really the decomposition of saliva on the surface of the tongue, due to electrolysis or the passage of a current through a liquid.

=Galvanism.= The science of voltaic, or current, electricity.

=Galvanizing.= Coating iron with a thin layer of zinc by immersing the object in the molten metal.

=Galvano-faradic.= In medical electricity the shocking-coil. The application of the voltaic current, induced by a secondary current (induction-coil), to any part of the body.

=Galvanometer.= An instrument for measuring current strength.

A magnetic needle influenced by the passage of a current through a wire or coil located near it.

=Galvanometer, Tangent.= A galvanometer provided with two magnetic needles differing in length, the shorter one serving to measure tangents, the longer being used for sine measurements of current strength.

=Galvanoscope.= An instrument, generally of the galvanometer type, used to ascertain whether a current is flowing or not.

=Generator.= An apparatus for maintaining an electric current, such as a dynamo, a faradic machine, a battery, etc.

=German-silver.= An alloy of copper, nickel, and zinc. Used chiefly in resistance-coils, either in the form of wire or in strips of the sheet-metal.

=Gold-bath.= A solution of gold used for depositing that metal in the electro-plating bath.

=Graphite.= A form of carbon. It occurs in nature as a mineral, and also is made artificially by the agency of electric heat.

=Gravity Battery.= (_See_ Battery, Gravity.)

=Grounded Circuit.= (_See_ Circuit, Grounded.)

=Ground-plate.= (_See_ Plate, Ground.)

=Ground-wire.= The contact of a conductor, in an electric circuit, with the earth. It permits the escape of current if another ground-wire exists.

=Guard Tube.= A tube inserted in a wooden or brick partition to insulate wires that may pass through it. These tubes are made of porcelain, gutta-percha, compositions of a non-conducting nature, and fibre.

=Gutta-percha.= Caoutchouc treated with sulphur to harden it; sometimes called vulcanized rubber or vulcanite. It is a product obtained from tropical trees, and when properly treated it is a valuable insulator in electrical work, particularly in submarine cables, since it offers great resistance to the destructive agencies of the ocean’s depths.

H

=Hand Generator.= A magneto-generator driven by hand for the generation of light currents.

=Harmonic Currents.= (_See_ Currents, Harmonic.)

=Harmonic Receiver.= A receiver containing a vibrating reed acted on by an electro-magnet. Such a reed answers only to impulses tuned to its pitch.

=Heat.= One of the force agents of nature. It is recognized in its effects through expansion, fusion, evaporation, and generation of energy.

=Heat, Electric.= Caused by a resisting medium, such as carbon or German-silver, when too much current is forced through it. The principle of the car-warmers, electric iron, electric chafing-dish, etc.

=Helix.= A coil of wire. Properly a coil of wire so wound as to follow the outlines of a screw without overlaying itself.

=Horse-power, Electric.= Meaning the same as in mechanics. Referred to when speaking of the working capacity of a motor or the power required to drive a dynamo.

=Horse-power Hour.= A unit or standard of electrical work theoretically equal to that accomplished by one horse during one hour.

=Horseshoe Magnet.= (_See_ Magnet, Horseshoe.)

=H-P.= Abbreviation for horse-power.

=Hydrometer.= An instrument employed to determine the amount of moisture in the atmosphere.

An instrument for determining through flotation the density or specific gravity of liquids and fluids. It consists of a weighted glass bulb or hollow metallic cylinder with a long stem on which the Baumé scale is marked. Dropping it into a liquid it floats in a vertical position, and sinks to a level consistent with the gravity of the fluid.

=Hydrometer, Baumé.= An apparatus for testing the gravity of fluids. The zero point corresponds to the specific gravity of water for liquids heavier than water. A gauge, valuable in testing acids and other fluids used in electrical work.

I

=Igniter.= A mechanical hand apparatus, in which a battery, induction-coil, and vibrator are located, and whose spark, jumping across a gap at the end of a rod, ignites or lights a gas flame, blasting-powder, or dynamite.

=I-H-P.= An abbreviation for indicated horse-power.

=Illuminating Power.= Any source of light as compared with a standard light--as, for instance, the illuminating power of an electric light reckoned in candle-power.

=Illumination.= A light given from any source and projected on a surface, per unit of area, directly or by reflection. It is stated in terms--as, for instance, the candle-power of a lamp. When speaking of an incandescent lamp we say it illuminates equal to four candle-power or it gives a light equal to sixteen candle-power.

=Immersion, Simple.= Plating, without the aid of a battery, by simply immersing the metal in a solution of metallic salt.

=Impulse.= The motion produced by the sudden or momentary action of a force upon a body. An electro-magnetic impulse is the action produced by the electro-magnetic waves in magnetizing a mass of soft iron and attracting to it another mass of iron or steel.

An electro-motive impulse is one where the force rises so high as to produce an impulsive discharge such as that from a Leyden-jar.

=Incandescence, Electric.= The heating of a conductor to red or white heat by the passage of an electric current. For example, an incandescent lamp.

=Incandescent Circuit.= (_See_ Circuit, Incandescent.)

=Incandescent Lamp-filament.= (_See_ Filament.)

=India-rubber.= (_See_ Caoutchouc and Gutta-percha.)

=Indicator-card.= The card used in galvanoscopes, volt and ampere meters, and other instruments. It is provided with a moving needle and is marked with a graduated scale.

=Induced.= Caused by induction, and not directly.

=Induced Current.= (_See_ Current, Induced.)

=Inductance.= That capacity of a circuit which enables it to exercise induction and create lines of force.

Inductance is the ratio between the total induction through a circuit to the current producing it.

=Induction, Back.= A demagnetizing force produced in a dynamo armature when a lead is given to the brushes. When the brushes are so set the windings on the armature are virtually divided into two sets: one a direct magnetizing set, the other a cross-magnetizing set which exerts a demagnetizing action on the other set. The position of the brushes on a dynamo or motor is indicated by their location, and if changed back induction will be the result.

=Induction-coil.= (_See_ Coil, Induction.)

=Induction, Electro-magnetic.= When negative and positive currents are brought towards each other against their material repulsive tendencies the result is work, or energy, and the consequent energy increases the intensity of both currents temporarily. The variations thus temporarily produced in the currents are examples of electro-magnetic induction. A current is surrounded by lines of force. The approach of two circuits--one negative, the other positive--involves a change in the lines of force about the secondary circuit. Lines of force and current are so intimately connected that a change in one compels a change in the other. Therefore, the induced current in the secondary may be attributed to the change in the field of force in which it lies. The inner and outer coils of wire about the soft iron wire composing an induction-coil are the best and simplest examples of electro-magnetic induction.

=Induction, Magnetic.= The magnetization of iron or other paramagnetic substances by a magnetic field. The magnetic influence of a bar excited under these conditions is shown by throwing iron filings upon it. They will adhere to both ends (that is at the negative and positive poles) but not at the middle.

=Inductor.= A mass of iron in a current generator which is moved past a magnet-pole to increase the number of lines of force issuing therefrom. It is generally laminated, and is used in inductor dynamos and motors of the alternating-current type.

=Influence, Electric.= Electric induction or influence which may be electro-static, current, or electro-magnetic.

=Influence Machine.= A static electric machine worked by induction, and used to build up charges of opposite nature on two separate prime-conductors.

=Installation.= The entire apparatus, building, and appurtenances of a technical or manufacturing plant or power-house. An electric-light installation would mean the machinery, street-lines, lamps, etc.

=Insulating Joint.= Used for the purpose of insulating a gas-pipe from an electric circuit.

=Insulating Varnish.= A varnish composed of insulating material, such as gums, shellac, or diluted rubber. Shellac dissolved in alcohol is perhaps the best. It is easy to make and dries quickly, making an insulating surface practical for almost every ordinary use.

=Insulation.= The dielectric or non-conducting materials which are used to prevent the leakage of electricity. The covering for magnet wires, and overhead conduits for power lines and electric lighting.

=Insulation, Oil.= Any non-combustible oil may be employed as an insulator to prevent electrical leakage in induction-coils, transformers, and the like. Its principal advantage lies in its being in liquid form, permitting of easy handling. Moreover, if pierced by a spark from a coil, it at once closes again without becoming ignited. A solid insulator, if pierced, is permanently injured.

=Insulator.= Any insulating substance or material to prevent the escape of current. The knobs of porcelain or glass to which wires are made fast.

=Insulator, Porcelain.= An insulator made of porcelain and used to support a wire.

=Intensity.= The intensity or strength of a current is its amperage. The strength of a magnetic field, its power to attract or magnetize.

=Internal Circuit.= (_See_ Circuit, Internal.)

=Internal Resistance.= (_See_ Resistance, Internal.)

=Interrupter.= A circuit-breaker. Any device which breaks or interrupts a circuit. It may be operated by hand or automatically.

The vibrator of an induction-coil.

The commutators of an armature.

=Isolated Plant.= The system of supplying electric energy by independent generating dynamos for each house, factory, or traction line.

=Isolation, Electric.= A term applied to “electric sunstroke.” Exposure to powerful arc-light produces effects resembling those of sunstroke.

J

=Joint.= The point where two or more electric conductors join.

=Joint Resistance.= The united resistance offered by a number of resistances connected in parallel.

=Jumper.= A short circuit-shunt employed temporarily around an apparatus, lamp, or motor to cut out the current.

=Jump-spark.= A disruptive spark excited between two conducting surfaces in distinction from a spark excited by a rubbing contact.

K

=Kaolin.= A form of earth or product of decomposed feldspar composed of silica and alumina. It is serviceable in insulating compounds.

=Kathode.= The terminal of an electric circuit whence an electrolyzing current passes from a solution. It is the terminal connected to the zinc pole of a battery or the article on which the electro-deposit is made.

=Key.= The arm of a telegraphic sounder by which the circuit is made and broken. A pivoted lever with a finger-piece which, when depressed, makes contact between a point and a stationary contact on the base.

=Keyboard.= A board, or table, on which keys or switches are mounted.

A switchboard.

=Kilowatt.= A compound unit; one thousand watts; an electric-current measure. Abbreviation, K-W.

=Kilowatt Hour.= The result in work equal to the expenditure or exertion of one kilowatt in one hour.

=Kinetoscope.= A photographic instrument invented by Edison for obtaining the effect of a panorama or moving objects by the display of pictures in rapid succession--in familiar parlance, “moving pictures.”

=Knife Switch.= A switch with a narrow and deep, movable blade, or bar of copper or brass, which resembles the blade of a knife. It is forced between two spring-clamps attached to one terminal so as to make perfect contact.

L

=Laminated.= Made up of thin plates, as an armature-core.

=Laminated Core.= (_See_ Core, Laminated.)

=Lamp-Arc.= A lamp in which the light is produced by a voltaic arc. Carbon electrodes are used, and a special mechanism operates and regulates the space between the carbons so that a perfect arc may be maintained.

=Lamp, Incandescent.= A lamp in which the light is produced through heating a filament to whiteness by the electric current. It consists of a glass bulb from which the air is exhausted and sealed, after the filament is enclosed. The ends of the filament are attached to platinum wires, which in turn are made fast to the contact-plates at the head of the lamp, so as to connect with the current.

=Lamp-socket.= A receptacle for an incandescent lamp. It is generally made of brass and provided with a key-switch to turn the current on and off.

=Latent Electricity.= (_See_ Electricity, Latent.)

=Lead.= (Not the metal.) An insulated conductor which leads to and from a source of power; an insulated conductor to and from a telegraph or telephone instrument; a circuit, a battery, or a station. Not a part of the line circuit.

That part of an electric light or power circuit which leads from the main to the lamps or motors.

=Leading-in Wires.= The wires which lead into a building from an aerial circuit.

The wires which lead in and out from a lamp, battery, or instrument.

=Leak.= An escape of electrical energy through leakage. This is more liable to occur in bare than in insulated wires. The escape of current from bare trolley wires is much greater than that from the insulated conductors, particularly in damp or rainy weather.

=Leclanché Battery.= (_See_ Battery, Leclanché.)

=Leyden-jar.= A type of static condenser. Its usual form is a glass jar. Tin-foil is pasted about its inner and outer surfaces covering about half the wall. The balance of the glass is painted with shellac or insulating varnish. The mouth is closed with a cork stopper, and through its centre a brass rod is passed which, by a short chain, is connected with the interior coating of the jar. The top of the rod is provided with a brass knob or ball, and from this last the spark is drawn.

=Lightning.= The electro-static discharge of clouds floating in the atmosphere. It is the highest form of frictional electricity, uncontrollable and very dangerous, since the strength of a single flash may run into hundreds of thousands of volts.

=Lightning-arrester.= An apparatus for use with electric lines to carry off to earth any lightning discharges that such lines may pick up; or it may be a form of fuse which burns out before the current can do any harm to the electrical mechanism.

=Line-insulator.= An insulator serving to support an aerial line.

=Lineman.= A workman whose business is the practical part of electrical construction in lines and conducting circuits.

=Link-fuse.= A plate of fusible metal in the shape of a link. It is used as a safety-fuse in connection with copper terminals.

=Liquefaction, Electric.= The conversion of a solid into a liquid by the sole agency of electricity in its heat action upon the solid.

=Liquid Resistance.= (_See_ Resistance, Liquid.)

=Lithanode.= A block of compressed lead binoxide, with platinum connections, for use in a storage battery.

=Litharge.= Yellow-lead. A chemical form of metallic lead.

=Load.= In a dynamo, the amperes of current delivered by it under given conditions of speed, etc.

=Local Action.= In a battery, the loss of current due to impurities in the zinc. The currents may circulate in exceedingly minute circles, but they waste zinc and chemicals and contribute nothing to the efficiency of the battery.

In a dynamo, the loss of energy through the formation of eddy currents in its core or armature, in the pole pieces, or in other conducting bodies.

=Lodestone.= The scientific name is magnetite. Some samples possess polarity and attract iron; these are called lodestones.

=Loop.= A portion of a circuit introduced in series into another circuit.

=Low Frequency.= A frequency (in current vibrations) of comparatively few alternations per second.

=Low Potential Current.= (_See_ Current, Low Potential.)

=Luminescence.= The power or properties some bodies have of giving out light when their molecular mass is excited. For example, phosphorus and radium.

=Luminous Heat.= The radiation of heat by electric current, which at the same time produces light. For example, the filament in an incandescent lamp.

=Luminous Jar.= A Leyden-jar whose coatings are of lozenge-shaped pieces of tin-foil between which are very short spaces. When discharged, sparks appear all over the surface where the small plates of metal nearly join.

M

=Magnet.= A substance or metal having the power to attract iron and steel.

=Magnet-bar.= A magnet in the shape of a straight bar. (_See_ Bar-magnet.)

=Magnet-coil.= A coil of insulated wire enclosing a core of soft iron through which a current of electricity is passed to magnetize the iron.

=Magnet-core.= An iron bar or mass of iron around which insulated wire is wound in order to create an electro-magnet.

=Magnet, Electric.= A magnet consisting of a bar of iron, a bundle of iron wires, or an iron tube, around which a coil of insulated wire is wound. When a current is passing through the coil its influence magnetizes the iron core, but directly the current ceases the magnetism disappears.

=Magnet, Field.= The electro or permanent magnet in a dynamo or motor, used to produce the area of electric energy.

=Magnet, Horseshoe.= A magnet of U shape with the poles or ends brought closer together than the other parts of the limbs. A soft iron bar is placed across the poles when not in use, as this serves to conserve the magnetism.

=Magnet, Permanent.= A term applied to a hard steel magnet possessing high retentivity, or the power to hold its magnetism indefinitely.

=Magnet, Regulator.= An electro-magnet whose armature moves in such a manner as to automatically shift the commutator-brushes, on a motor or dynamo, to a position which insures the preservation of both brushes and commutator-bars, and also produces a constant current.

=Magnet, Simple.= A magnet made of one piece of metal.

=Magnet Wire.= Insulated wire used for coils. Cotton or silk covered wire is the most serviceable for winding magnets.

=Magnetic Adherence.= The tendency of a mass of iron to adhere to the poles of a magnet.

=Magnetic Attraction and Repulsion.= The attraction of a magnet for iron, steel, nickel, and cobalt; also of unlike poles of magnets for each other. The like poles repel.

=Magnetic Circuit-breakers.= An automatic switch, or breaker, whose action is excited and controlled by an electro-magnet.

=Magnetic Concentration of Ores.= The separation of iron and steel from their gangue by magnetic attraction. It is applicable only when either the ore or the gangue is susceptible to the magnet.

=Magnetic Control.= The control of a magnetic needle, magnet, index, armature, or other iron indicator in a galvanometer, ammeter, or voltmeter by a magnetic field.

=Magnetic Dip.= The inclination from the horizontal position of a magnetic needle that is free to move in a vertical plane.

=Magnetic Field, Rotary.= A magnetic field resulting from a rotary current.

=Magnetic Field, Shifting.= A magnetic field which rotates. Its lines of magnetic force vary, therefore, in position.

=Magnetic Field, Uniform.= A field of uniform strength in all portions, such as the magnetic field of the earth.

=Magnetic Force.= The power of attraction and repulsion exercised by a magnet; the force of attraction and repulsion which a magnet exercises, and which, in its ultimate essence, is unknown to science.

=Magnetic Induction.= (_See_ Induction, Magnetic.)

=Magnetic Needle.= A magnet having a cup or small depression at its centre, and poised on a sharp pin of brass, so as to be free to rotate. Its N pole points to the north, and its S pole to the south. A compass needle.

=Magnetic Poles.= The terrestrial points towards which the north or south poles of the magnetic needle are attracted. There are two poles: the arctic, or negative, which attracts the positive or N pole of the magnetic needle; and the antarctic, or positive, which attracts the S pole of the needle.

=Magnetic Poles, False.= It has been established that there are other poles on the earth that attract the magnetic needle when the latter is brought into their vicinity. These are called false poles, and are probably caused by large deposits of iron lying close to the surface of the earth.

=Magnetic Separator.= An apparatus for separating magnetic substances from mixtures. It is used chiefly in separating iron ore from earth and rock. The mineral falls on an iron cylinder, or drum, magnetized by coils, and adheres there, while the earth or crushed rock drops below. The particles of iron are afterwards removed by a scraper. The machine is also used in separating iron filings and chips from brass, copper, or other metals, the iron adhering to the magnet, while the brass and other chips drop underneath.

=Magnetism.= The phenomena of attraction exerted by one body for another. It has been commonly understood that magnetism and electricity are very closely related, for without electricity magnetism could not exist, although it has not been shown clearly that magnetism plays any part in the generation of electricity. Magnetism is the phenomenal force exerted by one body having two poles (negative and positive) for like bodies. The horseshoe magnet or a bar of magnetized steel are the simplest examples of this. If both ends of the horseshoe were positive they would not attract, but would repel. If both ends of a bar were positive they would repel; but as one is negative, or north-seeking, and the other positive, they exert lines of force which attract like bodies, such as bits of iron, nails, and needles. No energy is required to maintain magnetism in a tempered steel object, such as the wiring about a soft iron core when it has been magnetized, but electric current must flow about the soft iron core in order to render it a magnet. So soon as the current ceases to flow the magnetism ceases and the soft iron fails to attract.

=Magnetism, Uniform.= Magnetism that is uniform throughout a mass of magnetic steel, or a core that is electro-magnetic.

=Magnetize.= To impart magnetic property to a substance capable of receiving it.

=Magnetizing-coil.= (_See_ Coil, Magnetizing.)

=Magneto Call-bell.= A call-bell used principally in telephone systems, and operated by a current from a magneto-electric generator. The current is excited by turning the handle at the side of the telephone-box before removing the receiver from the hook.

=Magneto-generator.= A current-generator composed of a permanent magnet and a revolving armature which is rotated between the poles of the permanent magnet.

=Main Circuit.= (_See_ Circuit, Main.)

=Main Feeder.= The main wire in a district to which all the feeder wires are attached.

=Main Switch.= The switch connected to the main wire of a line, or the main-switch controlling a number of auxiliary switches.

=Mains, Electric.= The large conductors in a system of electric light or power distribution.

=Make and Break, Automatic.= An apparatus which enables the armature of a magnet to make and break its circuit automatically.

=Make-and-break Current.= (_See_ Current, Make-and-break.)

=Mercurial Air-pump.= An air-pump operated by mercury to obtain a high vacuum, and used extensively for exhausting incandescent-lamp bulbs.

=Mercury Tube.= A glass tube sealed and containing mercury. It is so arranged as to give out fluorescent light when shaken or agitated by an electric current. For example, the Geissler tubes, the Cooper-Hewitt light, Crook’s tubes, etc.

=Metallic Arc.= An arc which forms between metallic electrodes.

=Metallic Circuit.= (_See_ Circuit, Metallic.)

=Metallic Conductor.= A conductor composed of a metal.

=Metallic Filament.= A metal wire used in an incandescent lamp--the filament.

=Metallic Resistance.= (_See_ Resistance, Metallic.)

=Metallurgy.= The art of working metals. Electro-metallurgy applies to the processes wherein electricity plays the most important part.

=Mica.= A natural mineral of sheet form and translucent, used extensively as an insulator in electrical equipment and mechanism.

=Mica, Moulded.= A composition composed of ground mica and shellac as a binder. When heated and pressed into various shapes and forms, it is a valuable insulator, and is employed for hooks, locks, tubes, sockets, and the like.

=Micanite.= An insulating material made by cementing laminations of pure mica together and cementing them with shellac or other suitable non-conducting adhesives.

=Molecular Adhesion.= The attraction of similar molecules for each other.

=Molecular Attraction.= The attraction of molecules, or physical affinity.

=Molecular Resistance.= The resistance which a mass or electrolyte offers when contained in an insulated vessel and a current of electricity is passed through it.

=Molecule.= One of the invisible particles supposed to constitute matter of every kind; the smallest particle of matter that can exist independently. It is made up of atoms, but an atom cannot exist alone.

=Morse Receiver.= The receiving instrument once universally used in the Morse system of telegraphy, but now superseded by the sounder.

=Morse Recorder.= An apparatus which automatically records on a ribbon of paper the dots and dashes of the Morse telegraph alphabet.

=Morse Sounder.= An electro-magnetic instrument designed to make a sharp, clicking sound when its armature lever is drawn down by the attraction of the magnets.

=Morse System.= A telegraphic system invented by Prof. S. F. B. Morse, in which, by means of alternating makes and breaks of varying duration, the dots and dashes of the Morse alphabet are reproduced and received at a distance through the agency of wires and the electro-magnetic sounder.

=Motor, Electric.= A machine or apparatus for converting electric energy into mechanical kinetic energy or power. The electrical energy is usually generated by a dynamo, and distributed on conductors to motors located at various points.

Electric motors are of two types--the A-C., or alternating current, and the D-C., or direct current.

=Motor-car, Electric.= A self-propelling car driven by stored electricity.

=Motor-dynamo.= A motor driven by a dynamo whose armature is firmly attached or connected to that of the dynamo. It is used for modifying a current. If the dynamo generates an alternating current of high potential, the motor converts it into a direct current of lower voltage but increased amperage.

=Motor-transformer.= A transformer which is operated by a motor.

A dynamo-electric machine provided with two armature windings, one serving to receive current, as a motor, the other to deliver current, as a generator, to a secondary circuit.

N

=N.= An abbreviation for the north-seeking pole in a magnet.

=Natural Magnet.= A loadstone.

=Needle.= A term applied to a bar-magnet poised horizontally upon a vertical point.

A magnetic needle, or the magnet in a mariner’s compass.

=Negative.= Opposed to positive.

=Negative Electricity.= The kind of electricity with which a piece of amber is charged by friction with flannel.

In a galvanic battery or cell the surface of the zinc is charged with negative electricity. Negative electricity, according to the theory of some scientists, really means a deficiency of electricity.

=Negative Electrode.= The same as Negative Element.

=Negative Element.= The plate not dissolved by the solution in a voltaic cell; the one which is positively charged.

The carbon, platinum, or copper plate or pole in a battery.

=Negative Feeder.= The conductor which connects the negative mains with the negative poles of a generator.

=Negative Plate.= (_See_ Plate, Negative.)

=Negative Pole.= (_See_ Pole, Negative.)

=Neutral Feeder.= The same as Neutral Wire.

=Neutral Wire.= The central wire in a three-wire system.

=Nickel-bath.= A bath for the electro-deposition of nickel.

=Non-arcing Fuse.= A fuse-wire which is enclosed in a tube packed with asbestos or silk, and which does not produce an arc when it fuses or blows out. It is practically noiseless, save for a slight hissing sound, accompanied by a light puff of smoke, which escapes from a venthole in the side of the tube.

=Non-conductor.= A material or substance offering very high resistance to the passage of the electric current.

=Non-magnetic Steel.= Alloys of iron incapable of being magnetized. They are composed of iron and manganese, nickel, steel, etc.

=Normal.= Regular. The average value of observed quantities. Normal current is a regular current without variations.

The force of a current at which a system is intended to work.

=Normal Voltage.= The same as Normal Current.

=North Pole.= The north-seeking pole of a magnet.

The pole of a magnet which tends to point to the north, and whence lines of force are assumed to issue on their course to the other pole of the magnet.

O

=O.= An abbreviation for Ohm.

=Oersted’s Discovery.= Oersted discovered, in 1820, that a magnetic needle tended to place itself at right angles to a current of electricity. This fundamental principle is the basis of the galvanometer, the dynamo, and the motor.

=Ohm.= The practical unit of resistance. A legal ohm is the resistance of a column of mercury one square millimetre in cross-sectional area and 106.24 centimetres in length.

=Ohm, True.= The true ohm is the resistance of a column of mercury 106.24 centimetres long and one square millimetre in cross-sectional area. An ohm may be measured by a No. 30 copper wire nine feet and nine inches long. If larger size wire is used the piece must be proportionately longer, since the resistance is less.

=Ohmic Resistance.= True resistance as distinguished from spurious resistance, or counter electro-motive force. (_See also_ Resistance, Ohmic.)

=Ohm’s Law.= The basic law which expresses the relations between current, electro-motive force, and resistance in active circuits. It is formulated as follows:

1. The current strength is equal to the electro-motive force divided by the resistance.

2. The electro-motive force is equal to the current strength multiplied by the resistance.

3. The resistance is equal to the electro-motive force divided by the current strength.

=O. K.= A telegraphic signal meaning yes, or all right. It is supposed to be a misspelled form of all correct, “Oll Kerrekt.”

=Okonite.= A form of insulation for wires and conductors; a trade name applied to insulations, and protected by copyright.

=Open Arc.= A voltaic arc not enclosed.

=Open Circuit.= (_See_ Circuit, Open.)

=Oscillating Current.= (_See_ Current, Oscillating.)

=Outlet.= That part of an electrolier or electric light fixture out of which the wires are led for attachment to incandescent light sockets.

=Outside Wiring.= The wiring for an electric circuit which is located outside a building or other structure.

=Overhead Feeders.= The same as overhead conductors.

=Overhead Trolley.= The system in which the current for the propulsion of trolley-cars is taken from overhead feeders or wires.

=Overhead Trolley-wire.= A naked, hard copper wire drawn at high tension, and suspended over or at the side of a car-track, and from which the trolley-wheel takes its current.

=Overload.= In an electric motor, an excess of mechanical load prevents economical working, causing the armature to revolve slowly and the wiring to heat. In this case heating implies waste of energy.

=Overload Switch.= A switch which operates automatically to open a circuit in line with a motor, and so save the motor from overheating or burning in the event of an overload.

P

=Paper Cable.= A cable insulated with waxed or paraffined paper.

=Paraffine.= A residuum of petroleum oil, valuable as an insulating medium in electrical work.

A hydro-carbon composition of the highest resistance known. It is extensively used in condensers and other electrical apparatus as a dielectric and insulator.

=Parallel Distribution.= A distributing system for electricity wherein the receptive contrivances are adjusted between every two of a number of parallel conductors running to the limits of the system. When two or more conductors connect two mains of comparatively large size and low resistance, they are said to be in parallel or in multiple. This order is easily pictured by imagining the mains to be the sides of a ladder and the conductors the rungs. In the latter the lamps are placed. It follows that the current flows from one main to the other through the conductors and lamps.

=Paramagnetic.= Substances which have magnetic properties, or those which are attracted by magnetic bodies. A paramagnetic substance has high multiplying power for lines of force, therefore a bar of iron which is a paramagnetic substance of the highest quality becomes magnetic when placed within a circle of electric lines of force. The first example of paramagnetic substance brought to the attention of man was the lodestone, from which the ancient mariners fashioned their crude compass needles.

=P-C.= An abbreviation for porous cup.

=Pear Push.= A push-button enclosed in a handle having the shape of a pear. It is generally attached to the end of a flexible wire cord.

=Periodic Current.= (_See_ Current, Periodic.)

=Permanency, Electric.= The power of conductors to retain their conductivity unaffected by the lapse of time.

=Permanent Magnet.= (_See_ Magnet, Permanent.)

=Phase.= One complete oscillation. The interval elapsing from the time a particle moves through the middle point of its course to the instant when the phase is to be stated.

Simple harmonic motion. Oscillation.

=’Phone.= An abbreviation for the word Telephone.

=Phonograph.= An apparatus for reproducing sound. It is vibratory and not electric in its action, except that the mechanism may be driven by electricity. It consists of a rotating cylinder of a waxlike material and a glass diaphragm carrying a needle-point that lightly touches the surface of the waxen cylinder. If the diaphragm is agitated the needle vibrates, making indentations in the surface of the wax. If the needle is set back and the cylinder rotated so as to carry the point over the indentations, the sound is given back through the vibration of the diaphragm.

=Pickle.= An acid solution used to cleanse metallic surfaces preparatory to electro-plating.

=Pilot Wires.= Wires brought from distant parts of electric light and power mains, and leading to voltmeters at a central station. Through their agency the potential energy of every part of the system may be measured.

=Pith-balls.= Balls made from the pith of light wood, such as elder. They are used in the construction of electroscopes and for other experiments in static electricity.

=Plant.= The apparatus for generating electric current, including engines, boilers, dynamos, mains, and subsidiary apparatus.

=Plate, Condenser.= In a static apparatus, the condenser having a flat piece of glass for a dielectric. It is mounted on an axle so that it may be revolved.

=Plate, Ground.= In a lightning-arrester, the plate connected to the earth or ground wire.

=Plate, Negative.= In a voltaic battery, the plate which is unattacked by the fluid. It is made of carbon, platinum, or copper.

=Plate, Positive.= (_See_ Positive Plate.)

=Plating-bath.= A vessel of solution for the deposition of metal by electrolysis. Used in electro-plating.

=Plating, Electro.= The process of depositing metal on surfaces of metals or other substances by the aid of an electrolyte and the electric current.

=Platinum Fuse.= A slender wire of platinum roused to incandescence by current, and used to explode a charge of powder or other combustible substance.

=Plug.= A piece of metal, with a handle, used to make electric connections by being inserted between two slightly separated plates or blocks of metal.

A wedge of metal, slightly tapered, and used to thrust between two conductors to close or complete a circuit.

=Plumbago.= Soft, lustrous graphite; a native form of carbon sometimes chemically purified. It is used chiefly in electrotyping for dusting the wax moulds to make the surface an electric conductor.

=Plunge-battery.= (_See_ Battery, Plunge.)

=Polar.= Pertaining to one of the poles of a magnet.

=Polarity.= The disposition in a body to place its axis in a particular direction when influenced by magnetism. For example, the attraction and repulsion at the opposite ends of a magnet. The N and S seeking poles of a compass needle is the simplest example.

=Polarity, Electric.= The disposition in a paramagnetic body to be influenced by electric waves and lines of force. The otherwise non-magnetic body or mass becomes magnetic to attract or repulse when influenced by electricity, but ceases to retain the phenomena after the electric influence is removed. A piece of soft iron wire, a nail, or a short rod of iron will become electro-polarized when a current of electricity is sent through a coil of insulated wire so wound that one end will be N the other S. So soon as the circuit is broken the polarity ceases.

=Polarization.= The depriving of a voltaic cell of its proper electro-motive force. This may be brought about through the solution becoming spent, or in the event of the acid being saturated with zinc, and so failing to act on the metallic zinc.

Counter electro-motive force due to the accumulation of hydrogen on the negative plate.

=Polarizing-current.= (_See_ Current, Polarizing.)

=Polar Surface.= The surface of a magnetic substance through which the magnetic flux passes in or out.

=Pole-changer.= An automatic, oscillating switch or contact-breaker which reverses the direction of the current.

=Pole, Negative.= The S pole in a magnet or compass needle.

=Pole, Positive.= (_See_ Positive Pole.)

=Pole-switch, Single.= A switch designed to open or close one lead only.

=Poles.= The terminals of an open electric circuit at which there necessarily exists a potential difference.

The terminals of an open magnetic circuit, or the ends of a magnetized mass of iron.

=Porcelain.= A fine variety of earthenware, valuable for insulators and insulating purposes.

=Porosity.= The state or property of having small interstices or holes. The opposite of density.

=Porous Cup or Cell.= A cup or cell made of pipe-clay or of unglazed earthenware through which a current of electricity can pass when wet or in a liquid. Porous cups are used in cells and batteries to keep two liquids apart, and yet permit electrolysis and electrolytic conduction.

=Positive Currents.= Currents which deflect the needle to the left.

=Positive Electricity.= The current that flows from the active element, the zinc in a battery, to the carbon. The negative electricity flows from the carbon to the zinc.

=Positive Electrode.= The electrode which is connected with the positive pole of a source of electric energy.

=Positive Feeders.= The lead or wire in a set of feeders which is connected to the positive terminal of the generator.

=Positive Plate.= In a voltaic cell, the plate which is acted upon and corroded. The current from the positive plate is negative electricity.

=Positive Pole.= The N pole in a magnet or magnetic needle. So called because it seeks the north or negative pole of the earth.

=Positive Wire, or Conductor.= The wire, or conductor, connected with the positive pole of any apparatus which produces electro-motive force.

=Potential, Electric.= The power to perform electric work.

=Potential Energy.= Capacity for doing work. Potential energy when liberated becomes actual energy for the performance of work.

=Power-generator.= Any source from which power is generated.

=Power-house.= A station in which the plant of an electric power system is operated and the current distributed to local or long-distance points. Power-houses are either primary or secondary stations. In the primary station the current is generated directly by the aid of mechanical power, either the steam-engine or the steam-turbine. The secondary station, or sub-station, is located at a distance from the main power-house, and has no mechanical means of generating current. The current, usually of high alternating voltage, is supplied to the sub-station from the main power-house; and by means of transformers and converters, the high-voltage current is transformed into one of lower E-M-F and higher amperage, for distribution over local lines.

=Power-unit.= The unit of electric power is the volt-ampere or watt.

=Pressure, Electric.= Electro-motive force or voltage.

=Primary.= A term used to designate the induction-coil in an induction-apparatus or transformer. It is an abbreviation for primary coil.

=Primary Battery.= (_See_ Battery, Primary.)

=Prime Conductor.= (_See_ Conductor, Prime.)

=Push-button.= A switch for closing a circuit by means of pressure applied to a button. The button is provided with a spring, so that when pushed in and released it flies back, reopening the circuit.

=Pyrogravure.= A process of engraving by the use of platinum points heated to redness by the electric current.

Q

=Q.= Abbreviation or symbol for electric quantity.

=Quadrant.= The quarter of a circle or of its circumference.

=Quadruple Circuit.= (_See_ Circuit, Quadruple.)

=Quantity.= The term is applied to express arrangements of electrical connections for giving the largest possible amount of current.

=Quantity, Electro-magnetic.= The electro-magnetic current measured by its intensity for a second of time.

=Quick-break.= A break affected in an electric current by the employment of a quick-break switch.

=Quickening.= The amalgamating of the surface of a metallic object before electro-plating it with silver. This secures better adhesion of the deposit, and is done by dipping the article into a solution of mercurial salts--one part of mercuric nitrate to one hundred parts of water.

R

=Radiant Energy.= Energy existing in the luminiferous ether and exercised in wave transmission, creating light or sound. Radium possesses the highest form of radiant energy.

=Radiate.= To emit or send out in direct lines from a point or points, as radiating heat, light, or sound. The radiations are sent out in all directions from a central point, just as a stone thrown in a pond of still water will radiate waves or ripples from the central point.

=Radiation.= The travelling or motion of ether waves through space.

=Radiator, Electric.= A series of plates or wire-coils heated by current. They radiate heat and so warm the surrounding air.

=Radiograph.= A photographic picture taken by the X-ray process.

=Receiver.= In telephony or telegraphy, an instrument for receiving the message as distinguished from the instrument sending or transmitting the message.

The telephone piece held to the ear is the receiver.

=Receiving End.= The end of a line where the operative currents are received, as opposed to the end at which they are transmitted.

=Receptacle.= A device for the installation of an attachment or extension plug. Used in connection with electric-lighting circuits.

=Recoil Kick.= Reaction resulting from a disruptive discharge.

=Recorder.= In telegraphy, the receiving apparatus for recording the dot-and-dash signals on a strip or tape of paper.

=Reduction.= The influence exerted without apparent communication by a magnetic field or a charged mass upon neighboring bodies. The induction-coil is a simple example of this force. The current passes through the primary or inner coil about a core of soft iron, and in doing so it develops lines of force in the secondary or outer coils, although no current is flowing directly through them from a battery or dynamo.

=Reduction Gear.= A gear which acts to reduce a speed below that of a motor in full motion without lessening its motive force.

=Refract.= To break the natural course of light in an elastic medium. The rays of light, as they pass from a rare into a dense medium, are refracted.

=Register, Electric.= An apparatus for registering and recording the movements of employés about a building. Press-buttons are arranged throughout the building, and when a man passes a station he presses the button, and the time is recorded by the apparatus.

=Regulator Magnet.= (_See_ Magnet, Regulator.)

=Relay.= A telegraphic or telephonic receiving instrument which opens and closes a local circuit through movements caused by the impulses of currents received. The relay battery may be very delicate so as to work with weak currents. The function of the relay is to open and close circuits for the admission of a new current to push on the sound or vibration to a more distant point. The main battery may be of any desired power.

=Relay Connection.= A connection used in telegraphy, including a local battery, with a short circuit, normally open, but closed at will by a switch and sounder, or other appliance. A very weak current will work the apparatus.

=Relay, Ordinary.= A relay that is not polarized.

=Relay, Repeating.= In telegraphy, a relay for repeating the signals through a second line.

=Reluctance.= Magnetic resistance.

=Repeater.= In telegraphy, an instrument for repeating the signals through a second line. It is virtually a relay which is controlled by the sender, and which, in turn, operates the rest of the main line. It is usually located at about the middle of the total distance covered.

=Repeating-station.= A telegraph station located on a long line, and occupying a position at the juncture of the sections into which the line is divided. The currents received through one section are repeated into the other sections by means of a repeater.

=Repulsion, Electric.= The tendency which exists between two bodies charged alike to mutually repel each other.

=Residual Charge.= (_See_ Charge, Residual.)

=Resilience.= The power to spring back to a former position. Electricity is resilient, although its elasticity cannot be measured accurately.

=Resin.= A solid inflammable substance or gum, and a good non-conductor in electrical work. It is the product obtained by distilling the sap of the pitch-pine. The name is also applied to the product of distilling the sap of other trees. Common resin, shellac, lac, Dragon’s-blood, and other substances of a similar nature are resins. They are all dielectrics, and the source of negative frictional electricity when rubbed with cotton, wool, flannel, silk, or fur.

=Resistance.= That quality of an electric conductor in virtue of which it opposes the passage of an electric current, causing the disappearance or modification of electro-motive force, and converting electric energy into heat energy.

=Resistance-box.= A box filled with resistance-coils connected in series and provided with a switch, so that any number of the coils may be cut out.

=Resistance, Carbon.= A resistance composed of carbon as a substitute for a coil of wire. Carbon rods are placed close together having an air space between them, with alternate ends connected. Piles may be built up of carbon plates, whose resistance is made to vary by changing the pressure.

=Resistance-coil.= A coil of wire metal or other substances having the power to resist a current of electricity.

A coil of wire used to measure an unknown resistance by virtue of its own known resistance. (_See also_ Coil, Resistance.)

=Resistance, Dielectric.= (_See_ Dielectric Resistance.)

=Resistance, Electrolytic.= The resistance of an electrolyte to the passage of a current decomposing it. It is almost entirely due to electrolysis, and is intensified by counter-electro-motive force. When a current of a voltage so low as not to decompose an electrolyte is passed through the latter, the resistance appears very high and sometimes almost infinite. If the voltage is increased until the electrolyte is decomposed the resistance suddenly drops to a point lower than the true resistance.

=Resistance, Internal.= The resistance of a battery, or generator, in an electric circuit as distinguished from the resistance of the rest of the circuit.

=Resistance, Liquid.= A liquid of varying specific gravity used to create resistance to the passage of the electric current.

Resistance effected by the use of liquid through which a current must pass to complete a circuit.

=Resistance, Metallic.= The resistance of metals to the electric current.

German-silver resistance as distinguished from that of water, carbon, or other substances.

=Resistance, Ohmic.= True resistance measured in ohms as distinguished from counter electro-motive force. (_See also_ Ohmic Resistance.)

=Resistance, Spurious.= The counter-electro-motive force. In its effect of opposing a current and in resisting its formation it differs from true resistance. True resistance diminishes current strength, absorbs energy, and develops heat. Spurious resistance opposes and diminishes a current without absorption of energy or production of heat.

=Resistance, Standard.= A known resistance employed to determine unknown resistances by comparison.

=Resistance, True.= The true resistance measured in ohms as distinguished from counter-electro-motive force.

=Resonator, Electric.= A small, open electric circuit with ends nearly touching. When exposed to electric resonance, or to a sympathetic electric oscillating discharge, a spark passes across the gap. The spark is due to inductance in the resonator.

=Retentiveness.= That property which enables steel to retain its magnetism.

=Return.= A line or conductor which carries current back to its starting-point after it has traversed a circuit. The best definition of a return is a circuit on which no new apparatus is installed.

=Return-circuit.= (_See_ Circuit, Return.)

=Return-circuit, Railway.= A grounded circuit used in trolley systems for ground returns through the tracks, they being joined by links or flexible wires so as to form perfect conductors. It is the negative side of the system, the positive being in the overhead or underground feed-wire or rail.

=Reversibility.= The principle by which any form of generator for producing a given form of energy may be reversed to absorb energy. The dynamo of the reversible type driven to generate current may be reversed and will develop power if a current is run through it.

=Rheostat.= An adjustable resistance. An apparatus for changing the resistance, without opening the circuit, by throwing a switch-bar across contact points.

=Rod Clamp.= A clamp used in the lamp rod of an arc-light to hold the carbon.

=Röntgen Effects.= Phenomena obtained by the use of the X or Röntgen rays.

=Röntgen-ray Screen.= A screen whose surface is covered with fluorescent material for the purpose of receiving and displaying the Röntgen image.

=Röntgen Rays.= A peculiar form of light radiation discovered by Röntgen, and which is emitted from that portion of a high vacuum tube upon which the kathode rays fall.

=Rotary Magnetic Field.= (_See_ Magnetic Field, Rotary.)

=Ruhmkorff Coil.= (_See_ Coil, Ruhmkorff.)

S

=Safety Fuse.= A device to prevent overheating of any portion of a circuit by excessive current. It generally consists of a strip of fusible metal which, if the current attains too great strength, melts and opens the circuit.

=Salt.= A chemical compound containing two atoms or radicals which saturate each other. One is electro-positive, the other electro-negative.

Salts are decomposed by electrolysis, and in separating they combine to form new molecules.

=Saturated.= A liquid is said to be saturated when it has dissolved all the salts it will take up.

=Search-light.= An apparatus for producing a powerful beam of light and projecting it in any desired direction.

=Secondary.= A term applied to the secondary coil of a transformer or induction-coil.

=Secondary Battery.= (_See_ Battery, Secondary.)

=Secondary Plates.= The plates of a secondary battery or storage-battery. When charged, the negative plate should be brown or deep reddish in color, and the positive slate-colored.

=Self-excited.= Electrified by its own current.

=Self-winding Clock.= A clock which automatically winds itself by electricity. It is operated by a small electro-magnetic motor which obtains its current from an outside source.

=Semaphore, Electric.= An apparatus for exhibiting signals. Used in the railway block system.

=Series.= Arranged in succession. When incandescent lamps are installed so that the current goes in and out of one lamp, and so on to the next and the succeeding ones, they are said to be arranged in series. It takes high E-M-F and current, or amperage, to operate such lamps.

Series batteries are arranged with the zinc pole of one connected to the carbon pole of the next.

=Series Arc Cut-out.= A device by means of which a short circuit is established past a defective lamp, thereby securing the undisturbed operation of all the other lamps in the circuit.

=Series Distribution.= A distribution of electricity in which the receptive devices are arranged in successive order upon one conductor, extending the entire length of the circuit.

=Series Dynamo.= A series-wound dynamo.

=Series Incandescent Lamp.= An incandescent lamp adapted for service in a series circuit.

=Series Motor.= A motor adapted for use in a series circuit; a motor whose field-coil winding is in series with the armature.

=Series, Multiple.= An arrangement of electric apparatus in which the parts are grouped in sets in parallel, and these sets are connected in series.

=Series Winding.= A method of winding a generator or motor in which one of the commutator brush connections is joined to the field-magnet winding. The other end of the magnet winding is connected with the outer circuit, and the second armature brush is coupled with the remaining terminal of the outer circuit.

=Service Wires.= Wires connected to the supply circuit or main wires, and which run into buildings to supply current for heat, light, and power.

=Shellac.= A resin gum, gathered from certain Asiatic trees. It is soluble in alcohol, and is used extensively in electric work as an insulator.

=Shifting Magnetic Field.= (_See_ Magnetic Field, Shifting.)

=Shock, Electric.= The effect upon the animal system of the discharge of an electric current of high potential difference. The voltage is the main element in a shock.

=Shoe.= As applied to electric railways, the casting employed to bear on the third rail to take in positive current and electro-motive force.

The cast-iron plate of an electric break, which, by magnetism, adheres to another iron surface.

=Short Circuit.= (_See_ Circuit, Short.)

=Shunt-box.= A resistance-box designed for use as a galvanometer shunt. The box contains a series of resistance-coils which can be plugged in or out as required.

=Shunt-winding.= A dynamo or motor is shunt-wound when the field-magnet winding is parallel with the winding of the armature.

=Silver-bath.= A solution of a salt of silver used in the electro-plating process.

=Silver-plating.= Depositing a coating of silver on a metallic surface by the acid of electro-metallurgy.

=Silver-stripping Bath.= An acid solution used for stripping silver from a metallic surface before re-plating it.

=Simple Circuit.= (_See_ Circuit, Simple.)

=Simple Immersion.= (_See_ Immersion, Simple.)

=Simple Magnet.= (_See_ Magnet, Simple.)

=Single-trolley System.= A trolley system employing only one overhead conducting wire, the track and ground serving as the return-circuit.

=Single-wound Wire.= Wire insulated by winding or overlaying with but a single layer of material.

=Sliding-condenser.= (_See_ Condenser, Sliding.)

=Snap-switch.= A switch so contrived as to give a quick break. A spiral spring is fastened between the handle and arm in such a manner that when the handle is drawn back the spring operates and quickly draws a knife-bar from the keeper, breaking the contact instantly and without the formation of an arc.

=Socket.= A receptacle for an incandescent lamp or plug.

=Solenoid.= A helical coil of wire of uniform diameter or cylindrical in shape. It is useful in experiments with electro-magnetism.

=Solution.= A fluid composed of dissolved salts; a mixture of liquids and fluids.

=Sound Waves.= Waves produced in an elastic medium by sonorous vibration, as in wireless telegraphy.

=Sounder.= In telegraphy, the instrument operated on by the key at the other end of a line. Various devices are employed to increase their resonance--as, for instance, hollow boxes. Sounders are generally placed on local circuits and are actuated by relays.

=Sounder, Repeating.= A telegraphic instrument which repeats a message into another circuit.

=S-P.= An abbreviation for single pole.

=Spark-arrester.= A screen of wire-netting fitted around the carbons of arc-lamps to prevent the chips or hot sparks from flying.

=Spark-coil.= A coil for producing a spark from a source of comparatively low electro-motive force. The induction-coil is an example.

=Spark, Electric.= The phenomenon observed when a disruptive charge leaves an accumulator or induction-coil and passes through an air gap.

=Spark-gap.= The space left between the ends of an electric resonator across which the spark springs.

=Sparking.= The production of sparks at the commutator, between the bars and the brushes of dynamos and motors. They are minute voltaic arcs, and should not be allowed to occur, as they cut away the metal and score the surface of the commutator.

=Spark-tube.= A tube used as a gauge to determine when the exhaustion of the vacuum chamber, or bulb, of an incandescent lamp is sufficiently high.

=Specific Gravity.= The relative weight or density of a body as compared with a standard. Water is usually taken as a standard for solids and liquids, and air for gases.

=Speed-counter.= An instrument which records the number of revolutions a shaft makes in a given time.

=Spent Acid.= Acid which has become exhausted. In a battery the acid becomes spent from combination with zinc; it also loses its depolarizing power.

=Spring-contact.= A spring connected to one lead of an electric circuit. It is arranged to press against another spring or contact, which it opens or closes by the introduction of a plug or wedge.

=Spring-jack.= An arrangement of spring-arm conductors under which plugs with wires attached can be slipped to make a new connection or to cut out certain circuits.

=Spurious Resistance.= (_See_ Resistance, Spurious.)

=Standard Candle.= (_See_ Candle, Standard.)

=Standard Resistance.= (_See_ Resistance, Standard.)

=Starting-box.= A resistance or shunt box used for letting current pass gradually into motors, instead of throwing on the full current at once.

=Static Electricity.= Electricity generated by friction; frictional electricity, such as lightning; electricity of high electro-motive force and practically uncontrollable for commercial purposes.

=Static Shock.= A term used in electro-therapeutics for describing the discharge from a small condenser or Leyden-jar; also the effect produced by the action of the vibrator of the induction-coil.

=Station, Central.= The building or place in which the electrical apparatus is installed for the generation of current; the headquarters of telephone lines.

=Steady Current.= An electric current whose strength is fixed or invariable.

=Stock-ticker.= An instrument employed to give quotations of stocks by telegraphic record. A paper tape runs through an electrical machine which prints on it the figures and letters that stand for stocks and their values. The whole system is operated from a station located in the Stock-exchange.

=Storage Accumulator.= (_See_ Accumulator, Storage.)

=Storage-battery.= (_See_ Battery, Storage.)

=Strength of Current.= Amperage; the quantity of current in a circuit.

=Stripping.= The process of removing electro-plating, or thin metal coatings, from an object before it is re-electro-plated.

=Stripping Liquid.= The liquid in a stripping-bath used for removing metals from surfaces before re-plating them.

=Submarine Cable.= A telegraphic cable laid at the bottom of the sea or any body of water.

=Submarine Search-light.= An incandescent light which works under water.

=Sub-station.= A generating or converting plant subsidiary to a central station, and placed so as to supply current in a district situated at a distance from the main power-house.

=Subway, Electric.= An underground passageway utilized for carrying cables and wires.

=Sweating.= A process by which the ends of cables are brought together and soldered.

=S-W-G.= An abbreviation for standard wire gauge.

=Switch.= A device for opening and closing an electric circuit. Made in a great variety of forms, such as push-button, telegraph-key, knife switch, automatic switch, lever switch, rheostat, etc.

=Switch-bell.= A combined bell and switch. The bell is operated when the switch is opened or closed.

=Switch-blade.= The blade of a switch; a conducting strip connecting two contact-jaws.

=Switch-board.= A board or table to which wires are led and connected with cross-bars or other devices by which connections can be made.

=Synchronize.= To agree in point of time; to effect concurrence of phase in two alternating-current machines, in order to combine them electrically.

T

=Table-push.= A push-button connected with a call-bell and fixed on a table for convenience in using.

=Tamadine.= A form of cellulose used for making the filaments of incandescent lamps. The material is cut into proper shapes, carbonized, and flashed.

=Tangent Galvanometer.= (_See_ Galvanometer, Tangent.)

=Tape, Insulating.= Prepared tape used in covering the bared ends of wires or joints.

=Tap-wires.= The conductors in trolley systems that at stated intervals, take the current from the mains and supply it to the bare feed-wires.

=Telegraph.= A system of electric communication invented by S. F. B. Morse, in which the dot-and-dash characters are used. There are various modifications of the system--double (or duplex), multiplex, and quadruplex--by means of which a number of messages may be sent out over the same wires at one time. Communication from place to place is had over wires mounted on poles, or by underground or submarine cables.

=Telegraphy, Wireless.= A system of telegraphy carried on without the aid of wires, using instead the ether waves of the atmosphere to conduct the vibrations overhead, and the ground, or earth, as a return. The present limit of its working is about four thousand miles.

=Telephone.= An instrument and apparatus for the transmission of articulate speech by the electric current. A magnet is encased in a tube and is encircled at one end by a coil of fine, insulated wire. A diaphragm of thin iron is fixed in front of the coil and close to the end of the magnet. The ends of the coil-wires are connected with a line, at the other end of which another and similar instrument is installed. The voice causes the sending diaphragm to vibrate, and these waves are transmitted to the other instrument, where they can be heard through contra-vibrations of the receiving diaphragm.

=Telephone, Long-distance.= A telephone of modern construction, in which the sound-recording mechanism is so sensitive as to make the vibrations of the voice audible at long distances. It will work satisfactorily at one thousand or even fifteen hundred miles.

=Terminal.= The end of any open electric circuit, or of any electric apparatus, as the electrodes of a battery.

=Thermostat, Electric.= An apparatus similar in some respects to a thermometer, and used for closing an electric circuit when the latter becomes heated. It is used in connection with automatic fire-alarms to give warning of fire. For this purpose the metal coil is arranged to close the contact at a temperature of 125° F. It usually consists of a compound strip of metal wound in the form of a spiral and fastened at one end. To this end one terminal of a circuit is connected. The expansion of the coil causes its loose end to touch a contact-point and close the circuit.

=Third Rail.= A railway motive system which employs a third rail instead of an overhead trolley feed-wire. The rail is laid on or under the surface of the ground and properly insulated. A shoe from the car bears on the rail and takes up the current.

=Three-wire Circuit.= A system invented by Edison for the distribution, from two dynamos, of current for multiple arc or constant potential service. One wire or lead starts from the positive pole of one dynamo, another from the negative pole of the other dynamo, and between the two dynamos the central or neutral lead is made fast.

Now the dynamos may generate a current of 220 volts, and send it, at this strength, through the outer wires; but if lamps are connected between either of the outer and the neutral wires, the current, passing through the lamps, will be reduced to 110 volts.

=Time-ball, Electric.= A ball which, by means of electricity, is made to drop from the top of a high pole, giving a visual signal for twelve o’clock or any other hour that may be designated.

=Traction, Electric.= The propulsion of a car or conveyance by means of electricity.

=Transformer.= In alternating-current systems, the induction-coil by means of which the primary current, with high initial electro-motive force, is changed into a secondary current with low initial electro-motive force.

=Transmission.= The conveyance of electric energy and currents from one point to another by the proper means of conduction.

=Transmitter.= An instrument which originates the signals which are sent through a line or circuit. The Morse key in telegraphy and the Blake transmitter in telephony are examples.

=Tri-phase.= Three-phase.

=Trolley.= A contact-wheel of bronze which rolls under the supply-wire in an overhead traction system and takes off the current necessary to run the car motors.

=Trolley-wheel.= The same as Trolley.

=Trolley-wire.= The overhead wire in a traction system which feeds the current through a trolley-wheel and pole to the motors of a car running underneath.

=True Ohm.= (_See_ Ohm, True.)

=True Resistance.= (_See_ Resistance, True.)

=Two-wire Circuit.= The single system universally used for light and power transmission of current.

U

=Undulating Current.= (_See_ Current, Undulating.)

=Uniform Magnetic Field.= (_See_ Magnetic Field, Uniform.)

=Unipolar.= Having but one pole.

=Unit.= The single standard of force, light, heat, magnetism, attraction, repulsion, resistance, etc.

V

=Vacuum.= A space empty or void of all matter; a space from which all gases have been exhausted.

=Vacuum Tubes.= Tubes of glass through which electric discharges are passed after the gases have been partially removed; for example, the X-ray tube of Röntgen and the Crooke tubes.

=Vibrator, Electro-magnetic.= The make-and-break mechanism used on induction-coils, or other similar apparatus, in which, through alternate attractions, an arm or spring is kept in motion.

=Vitriol, Blue.= A trade name for copper sulphate. (Bluestone.)

=Vitriol, Green.= A trade name for ferrous sulphate. (Copperas.)

=Vitriol, White.= A trade name for zinc sulphate. (Salts of zinc.)

=Volt.= The practical unit of electro-motive force; the volume and pressure of an electric current.

=Voltage.= Electric-motive force expressed in volts--as, a voltage of 100 volts.

=Voltaic.= A term derived from the name of the Italian scientist Volta, and used in many ways as applied to electrical current and devices. Formerly the term galvanic was commonly employed.

=Voltaic Electricity.= (_See_ Electricity, Voltaic.)

=Voltimeter.= An instrument for measuring the voltage of a current.

=Vulcanite.= Vulcanized rubber. Valuable for its insulating properties and inductive capability.

W

=Watt.= The practical unit of electrical activity; the rate of work or rate of energy. It is a unit of energy or of work represented by a current of one ampere urged on by one volt of electro-motive force.

The volt-ampere.

The standard of electrical energy corresponding to horse-power in mechanics.

=Watt-hour.= A unit of electric energy or work; one watt exerted or expended through one hour.

=Waves, Electro-magnetic.= Ether waves caused by electro-magnetic disturbances affecting the luminiferous ether.

=Welding, Electric.= Welding by the use of the electric current.

=Wimshurst Electric Machine.= An influence machine for producing high potential or static electricity. Thin disks of glass are mounted on insulated bearings and revolved by power. Brushes collect the frictional electricity, which is discharged into a Leyden-jar or other form of accumulator. It is of no practical use excepting in electro-therapeutics.

=Wire, Flexible.= A cord of fine wire strands laid together and insulated so that it may be easily bent or wrapped.

=Wiring.= Installing wires so as to form a circuit for the conveyance of current for light, heat, and power.

X

=X-rays.= A curious phenomenon involving the radiation of invisible rays of light, which have the power to travel through various opaque bodies. The rays are used in detecting foreign substances in the human body and for photographing invisible or hidden objects without disturbing their surroundings.

=X-ray Lamp.= A high vacuum tube lamp whose interior walls are covered with crystals of calcium or other fluorescent substances, and which, when exposed to the X-rays, give out a luminous light.

Y

=Yoke.= A piece of soft iron which connects the ends of two portions of a core on which wire coils are wound. It is located at the ends farthest from the poles.

The soft-iron bar placed across the ends of a horseshoe magnet to retain its magnetism.

Z

=Zinc-battery.= A battery which decomposes zinc in an electrolyte, thereby producing a current.

=Zinc Currents.= Negative currents.

=Zinc-plating.= The employment of zinc in electro-plating.

THE END

Transcriber’s Notes

Inconsistent spelling, hyphenation, etc. have been retained, unless mentioned under Changes Made below. Technical descriptions have been kept as printed, even when they seem doubtful, wrong or dangerous.

Depending on the hard- and software and their settings used to read this text, not all elements may display as intended.

Changes Made

Footnotes and illustrations have been moved outside text paragraphs.

Where letters (such as V or L) are used to denote a shape rather than the letter, they have been transcribed as [V] or [L] for consistency with other, similarly used letters such as [U].

Some minor obvious typographical errors have been corrected silently.

Page 108: "called Nobile’s pair" changed to "called Nobili’s pair".

Page 182: "shallacked" changed to "shellacked".

Page 184: "(A, B, and C) and A A, B B, and C C)" changed to "(A, B, and C and A A, B B, and C C)".

Dictionary: several entries have been moved to their proper alphabetical position.

Page 334: "modern applications of phenonema" changed to "applications of phenomena

Page 372: "Coil, Ruhmkoff" changed to "Coil, Ruhmkorff".

Page 382: "Daniells" changed to "Daniell".

Page 396: "graphite a native; form of carbon" changed to "graphite; a native form of carbon".

Page 401: "Ruhmkoff Coil. (See Coil, Ruhmkoff.)" changed to "Ruhmkorff Coil. (See Coil, Ruhmkorff.)"