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All special kinds of the alarms for house protection consist of modifications in the method of making the contact, suitable for special purposes, such as laying sheets of tin under the carpet to make contact with the wires when the carpet is stepped upon. Means are also now generally introduced for indicating which window the signal comes from. This is done by leading the wires from each window separately through an annunciator, which shows through which wire, and consequently from which window the signal came. The entire wiring of houses is also frequently connected with the police oflice by wire, so that they are notified of any tampering with the house in the absence of its occupant. An ingenious method of protecting safes of great value by surrounding them with a wire net is also in extensive commercial use. The safe is completely enclosed in a wooden cabinet, the sides and doors of which are lined with a compli. cated network of fine wires. When the doors of the cabinet surrounding the safe are closed, the wires in the doors are connected with the rest of the wires by springs, and a continuous circuit is formed all around the safe, through which a delicate current is passed by the central office watchmen until the hour for reopening the safe. The complication of the wires is such that it would be impossible to disconnect any of them, or even substitute other wires without disturbing the delicate current which is kept on them. For further safety there is sometimes introduced a machine, which automatically changes the combination of wires during the night, at times known only to the watchmen.
ELECTRIC CLOCKS AND ELECTRIC TIME SYSTEM. Electricity is used in connection with clocks in several ways. It is used in place of a spring for actuating the clock; for moving the hands of a number of dummy clocks, in accordance with the motions of the hands of a standard clock; for sending the pendulum beats of a standard clock over wires to observatories, the shops of clock-makers, etc., and for periodically winding up the springs of ordinary clocks. For the first class—that of furnishing the motive power of clocks--the use is based upon the idea of securing greater uniformity of running by keeping the pendulum in motion by electricity instead of by spring or weight. For this purpose a great many special devices have been made, none of which are of particular importance. The use of electricity for keeping a number of clocks in agreement with a standard clock is of more importance. The pendulum of the standard clock is arranged to make an electric contact at each swing. By touching a spring, or better, by dipping its lower extremity into a trough of mercury at the lowest point of the swing, the pendulum and the trough being made the terminal of an electric circuit, an impulse is sent over the wire at every vibration of the standard pendulum. Upon this wire, in all desired buildings, are placed receiving clocks, consisting of a dia! with hands fastened to toothed wheels. A magnet connected to the wire moves the wheel of the second hand one tooth as each impulse comes over the wire, thus keeping the second hand, and consequently the connected minute and hour hands, in positions corresponding exactly to those of the hands of the standard clock. This is the foun. dation of a considerable business known as time telegraphing. The use of the telegraph for simply transmitting taps representing the pendulum beats of a standard clock, for the use of observatories, is the most important division of the subject. The standard clock is arranged to close the circuit at each vibration, as previously described. The signals so produced are carried to clock-makers, observatories, etc., on suitable wires. In New York city, where this system is extensively used, and where several distributing circuits are required, the impulses of the standard člock are used to operate a multiplying instrument, which reproduces them at the same moment on a number of different wires.
The time-ball dropped at noon in New York city by the Western Union telegraph co. is an application of this system. At a few minutes before twelve, the standard clock in the Naval observatory at Washington is connected with one of the wires running to New York. At the same time the ball is hoisted to the top of the flag-staff in New York, and the hoisting rope is secured by a catch controlled by an electro-magnet. This magnet is connected to the wire to Washington. At the heat of twelve o'clock the pendulum itself of the clock at Washington sends the impulse which loosens the catch, and the ball on the flag-staff at New York falls. To guard against error due to slow descent caused by high winds, etc., the ball is arranged to strike a lever when it reaches the bottom, and send another signal back to Washington. This shows the Washington observer whether the ball was behind time in falling. If it is found to be late, it is immediately hoisted again as a signal of error.
The fourth class-namely, of clocks in which electricity is used to wind up the main spring periodically, is not of much importance. The object is to save the trouble of winding up, and secure a little greater uniformity of action. The spindle, ordinarily turned by the winding key, is provided with a small electric-motor actuated by a battery placed in any convenient closet. At uniform intervals the motor winds up the clock.
ELECTRIC FUSE is an apparatus for firing explosives in mines by means of the heating effect of electricity in a wire. The faculty of electricity of traveling quietly through a wire of large size and developing suddenly into intense heat when it meets a small wire, affords an excellent means of setting fire to explosive charges from a safe dis. tance and at will. The use of electric fuses has therefore developed very rapidly, and they are now employed exclusively for firing all large submarine mines and torpedoes and for the majority of ordinary blasts. The fuse consists of a suitable small box, A, con
taining a piece of wire, fig. 1, sufficiently fine to be made red bot by the current which is to be used. This wire is soldered to supports on the ioside of the box, which are led
through its walls from rigid connectors on the outside, to which the main cables, C, are attached. The object of arranging the fine wire in this manner is that the strain of the heavy connecting, cables may be spent on the box and
not on the fine wire within ; the wire, being extremely thin, would be broken A by even a very slight pull. The box is then filled witli fine-grained powder, B,
and the lid tied down. The wires of the fuse are then carefully joined to the
long conducting wires which lead to the battery. They should be of copper - and as thick as is convenient, so as to offer very little resistance ; No. 16
gauge copper wire is a suitable size. The fuse is then introduced into the charge to be fired : if it is for a submarine explosion the powder is contained in a canister, the neck of which, after the introduction of the fuse, is carefully fastened by means of cement. When contact is made with the battery, which is effected through the intervention of a suitable key, the current traversing the platinum wire renders it incandescent, which fires the fuse, and thus the ignition is communicated to the charge in which it is placed.
The heating effect depends more on the size than on the number of the plates of a battery, for the resistance in the connecting wires is small. An iror wire may be melted by a single Wollaston's element (see ĞALVANIC BATTERY), the zinc of which is 8 in. by 6. Hare's battery has received its name, deflagrator, on account of its greater heating effect, produced by the large surface of its plates. Batteries for this purpose are now made up in boxes suitable for carrying, fig. 2, and provided with a key for starting the current which is to fire the mine.
When any circuit is closed, a definite amount of heat is produced throughout the entire circuit ; and the amount of heat produced in any particular part of the circuit is great
er the greater the proportion which Fig. 1.
the resistance of this part bears to the entire circuit. Hence, in firing mines, the wire to be heated should be of as small section and of as small conductivity as practicable.
These conditions are well satisfied by platinum, which has over iron the advantage of being less brittle, and of not being liable to rust. Platinum too has a low specific heat, and is thus raised to a higher temperature by the same amount of heat than a wire of greater specific heat
On the other hand, the conducting wires shou a present as small a resistance as possible, a condition satisfied by a stout copper wire ; and again, as the heating effect of any circuit is proportional to the square of the strength, and as this is directly as the electromotive force and inversely as the resistance, a battery with a high electro-motive force and small resistance, such as Grove's or Bunsen's, should be selected.
ELECTRIC FISHES. See ELECTRICITY, ANIMAL.
ELECTRIC GAS LIGHTING. Electricity is very extensively used for lighting gas, In cases where the fixtures are out of reach, as in public halls etc., the wire is carried around the gas fixtures, being interrupted by a small break or space over each burner, so as to cause sparks at these points when a current is passed. For these lighters an electrical machine is provided which will generate sufficient electricity when its crank is turned to travel through the wire and jump over all the breaks. The sparks produced at the breaks are sufficient to set fire to the gas, which of course has been previously turned on, and all the burners are lighted at once. Another system which can be used only when each burner is within reach is employed where it may be desired to light each burner separately. It consists of a number of wires permanently connected to a galvanic battery and induction coil, each wire being led separately to one of the burners, and provided with a trigger for bringing the wires in contact, and so producing a spark when any particular burner is to be lighted. In this arrangement the closing of either one of the circuits at its burner produces a considerable spark by the inductive action of the induction coil, and ignites the gas.
ELECTRIC HEATING. Heat is developed by the passage of a current through any conductor, and the greater the resistance of the conductor the higher will be the temperature to which it is raised by the passage of the current. This is the principle upon
which all electric heaters are constructed. These heaters have come into considerable use since 1895 for both heating apartments, street cars, etc., and for cooking. Their general construction is as follows: Wire of high resistance is embedded in asbestos, fire clay, or other refractory material and built up into plates of large radiating surface, these being generally enclosed between iron plates. The current is passed through the resistance wire which at once becomes very hot and in turn heats up the refractory material and the enclosing iron. When the heater has been brought up to the required temperature the current may be turned all or partly off, and owing to the nature of the materials used the heater will retain its heat for a long time.
ELECTRICITY. The name given to the unknown matter or force, or both, which produces electric phenomena. Electricity, however produced, is believed to be one and the same thing, although static, voltaic or galvanic, magneto, thermo, and animal electricity are used as convenient terms to signify the origin of the electricity. They are no longer considered as different kinds of electric force. There have been numerous hypotheses as to the nature of electricity, the three most important of which are known as the single fluid theory, the double fluid theory, and Hertz's theory of electro-magnetic radiations, the latter theory being at the present time most generally accepted. The single fluid theory assumes that electricity is due to the presence of a single, tenuous, imponderable fluid, whose particles mutually repel each other but which are attracted by all matter and that every substance possesses a definite capacity for holding this electric fluid. When this capacity is just satisfied, no electrical phenomena are manifest; when less than this quantity is present the body becomes negatively excited, and when more, positively excited. Another view considers electricity to be due to differences of ether pressure, electricity being the ether itself and the pressure or electromotive force being the differences of ether pressure. The double fluid theory assumes the presence of two imponderable fluids, one negative and the other positive. The particles of positive fluid are assumed to repel one another, as do also the particles of negative fluid, but particles of opposite polarities attract each other. The two fluids are strongly attracted by matter, and when both are present in matter to an equal extent no electrical phenomena are present, as the two fluids neutralize each other, but when two bodies are rubbed together the fluids separate, one remaining in one body and the other passing to the other body. Hertz's theory assumes electricity to be due to vibrations of the ether, and his remarkable researches have shown that when an impulsive discharge is passing through a conductor, ether waves are propagated and radiated in all directions in the space surrounding the conductor. These waves are similiar in all respects to those of light except that they are much longer. These electro-magnetic waves possess the same velocity and the same characteristics as light vibrations. When impulses of electricity pass from one end of a long conductor to the other, the pulses are supposed to travel through the universal ether surrounding the conductor rather than through the conductor itself. In the free ether the velocity is the same as that of light, but in the intermolecular ether of conductors the velocity depends upon the nature of the medium.
Friction between two substances always produces electrical separation. In general when two bodies are thus electrified that one becomes negative whose particles are more easily removed by friction. Differences of temperature also affect the electrical condition of bodies, a warm body being usually negative when rubbed on a cold piece of the same substance. It has been found that the degree of electrification produced by rubbing two substances together is independent of the pressure and the amount of surface in contact but depends on the materials and the velocity with which they are rubbed against one another. The amount of the charge is not proportional to the actual mechanical friction, so it is doubtful if the friction is the real cause of electrification.
Incidentally, the minute quantities of electricity produced in this way have enormously high pressure enabling them to form sparks of considerable length; and the identity of different kinds of electricity was not known till the time of Franklin, when it was proved that the sole difference was one of quantity and pressure. See ELECTRICITY, STATIC. Electricity of the continuously flowing form was first derived from galvanic batteries (q. v.), and its properties and applications as far as developed with these sources, were known and treated under the title of Galvanism. The production of electricity from chemicals, however, was too expensive to permit of its being extensively used in industrial processes. The invention of dynamo-generators, first known as magneto-generators (q. v.), during the last twenty years, has reduced the cost of electricity to one hundredth of its cost from chemical batteries, and it is now used extensively in many arts. The wide usefulness of electricity results from the peculiarity of its powers or properties, and its possession of them in a very high degree. It travels with incredible velocity. This has rendered the telegraph possible. It attracts objects at a distance, hence its value for moving the clappers of bells, running motors, etc. It decomposes chemicals, giving us electrolysis, electro-plating, electro-chemistry, electro-metallurgy, etc., and the analysis of compounds previously unknown. It is readily convertible into heat in a wire, giving us the electric light. It is attractive to the engineer as a force because its laws of action are very accurate and well understood. Any results of electrical action can therefore be predetermined with a degree of certainty exceeding that found in any other branch of engineering.
volts Current Resistance, or Ampères
ELECTRICITY.-1. Galvani's experiment on frog's legs. 2. Dry pillar. 3. Ground return «
column. 9. Generation of heat by galvanic current. 10. Galvanic incandescence.