T

Leyden Jar.-This is a glass jar, with a coating of tin-foil pasted carefully inside and out, extending to within a few inches of the mouth. This last is generally closed by a wooden stopper, through which passes the stalk of a brass knob or ball surmounting the whole. The connection between the inside coating and the ball is completed by a chain extending from the stalk to the bottom of the jar. If this jar be put on an insulating stool, so that sparks can pass from the prime conductor of a machine to the knob, when the jar is thus insulated, one or two sparks pass, and then the charge seenis complete, for no more sparks will follow, though the action of the machine is continued; or, if they do, they are immediately dissipated from the knob in a brush discharge. If, then, however, the knuckle of the experimenter be brought near the outer coating, sparks begin again to pass freely; and for every spark of electricity that passes between the machine and the knob, a corresponding spark of the same name passes between the knuckle and outer coating. This continues for some time, and then the jar appears to be again saturated. It is now said to be fully charged. The outside of the jar can, in this state, be handled freely, and if it be still on the insulating stool, so may also the knob, although, when the hand first approaches, it receives a slight spark. But if, when the experimenter has one hand on the outer coating, he bring the other hand to the knob, before it can reach it, a straight, highly brilliant spark passes between the knob and his hand, and he experiences a shock of great violence. If he try the same thing again, a feeble spark and shock again ensue, and the jar is now thoroughly dis charged. As it is highly inconvenient, if not dangerous, to discharge the jar through the body, discharging tongs are used for that purpose, which consist of two brass arms ending in balls, and moved on a hinge by glass handles.

The velocity of electrical discharge is found to be about 192,000 m. per second.

ELECTRICITY, STORAGE OF. The supplying of electricity from storage or "secondary" batteries for all kinds of purposes, such as running street-cars, etc., is be. coming very common. The principle upon which the storage depends is that of de composing combined chemicals by the action of electricity from the source at hand, The chemicals so torn apart, reunite as soon as they are allowed to, by the completing of the circuit, and in recombining generate or give off nearly as much electricity as was used upon them at first. The materials usually employed are sheets of lead smeared with a paste of red lead.

ELECTRIC LIGHTING. The first practical application of electricity was as a means of furnishing artificial light, and this has been the most extensively developed of its uses. The first electric light was that made by sir Humphry Davy in 1809, at the Royal institution in London, when on separating the ends of the wires leading from a battery of two thousand cells, which was the largest battery that had ever been constructed, a brilliant light was seen. This was due to the heating of the ends of the wire

FIG. 1.

FIG. 2.

by the passing current. A few lamps were made to give light in this way, with a simple apparatus illustrated in fig. 1, but electricity was too expensive to allow lights so produced to be used to any extent until the invention of dynamo generators of electricity, about 1870. Then Jablochkoff introduced his electric candle, which was seen by all the world in Paris in 1870. And although it did not furnish a means of producing an economical light, it did a great deal to awaken public interest in the new means of illumination. The Jablochkoff candle was immediately followed by a number of other lamps of greater simplicity, and consequently of great commercial value. These improvements in the lamp, together with the improvements in dynamos, have advanced the art of electric lighting to a position of successful competition, with all other methods of artificial illumination. Its development has been greater if possible than that of any

other branch of electricity. The electric light is in use in every city and town in the U. S. It is estimated that there are now in use in this country one and a half million are lights and three million incandescent lights. We have not space to describe even the principal steps which have led to all the improvements in the apparatus now used, nor to describe the different kinds of apparatus employed at present. We can only review the two principal methods of lighting. There are two entirely distinct systems of producing light by electricity-the "arc" and the "incandescent." The "arc" light is produced by causing a continuous current of electricity to jump across a gap of about one sixteenth of an inch between the extremities of two rods of carbon to which the electricity is supplied, fig. 2. The heat developed brings the carbons to an intense brilliancy, and is the means of producing the most powerful artificial light known. As the ends of the rods are consumed by the current they are now brought nearer together by suitable automatic mechanism known as the regulator of the lamp, in the improved lamps of to-day, fig. 3. It is chiefly in these regulators that the inventions have been made. The current in jumping from one carbon to the other takes a curved path, whence the name of the electric arc. The current in passing from the positive to the negative rod carries small particles of the carbon with it. This causes the end of the positive carbon to become hollowed out while the negative carbon is built up to a point by the particles added to it. The hollowed end of the positive carbon is called the crater, and in lamps for street-lighting is placed above the other, so that it will help to throw the light down upon the ground. The arc light is very powerful, bluish white in color, and somewhat unsteady, and is therefore suitable only for out-door illumination. The incandescent light is produced by the heating of a fine wire or filament to incandescence by the passage of the electric current through it. The light so produced is soft, steady, and agreeable, and suitable for indoor illumination. To prevent the filament or wire from being burned up by the intense heat to which it is subjected, it is sealed up in a glass bulb from which all the air has been exhausted, or displaced by some substance which is not a supporter of combustion.

ELECTRIC LOOM. See WEAVING.

FIG. 3

ELECTRIC MOTORS, machines for converting electricity into mechanical power, in construction and principle identical with dynamos (see MAGNETO-ELECTRIC MACHINES), and differing only in a few minor points. They are fitted with one or two appliances usually, for stopping and starting them and regulating their speed and power. Being in fact dynamos, they have the same efficiency, of about 90 per cent.; that is to say, a motor which is supplied with 100 horse-power of electricity will furnish about 90 horse-power to the machinery it is driving. The special advantages are that they are small, light, clean, easy to manage, and can receive any amount of power through a small wire led into the building at some convenient out-of-the-way place. Owing to these advantages, power can be obtained and used in many places where it would be out of the question without the aid of electricity. Street cars may be propelled by it, the shafting on the different floors of factories may be driven without connecting belts passing through the floors, and power may be obtained in places where the amount needed is so small that the expense of a steam engine and attendant would be out of proportion and too great. Among the machines frequently requiring power in such places may be mentioned small elevators, ventilating fans, sewing-machines, pumps, coffee mills, printing-presses, lathes, etc. The entire cost of power for driving a sewing-machine by a motor continuously every day does not exceed $1.50 a month. There are in use in the U. S., furnishing small amounts of power for these and similar purposes, over 10,000 electric motors. There are two general methods of supplying the electric current for operating motors, known respectively as the multiple arc system, which is the same as that by which incandescent lights are supplied, and the series system, by which are lights are supplied. See ELECTRIC LIGHTING.

In the multiple arc system the electricity is kept at constant pressure, while the quantity which passes into any machine connected to it depends upon the size of the passage which is offered to the electricity, in the same way that the amount of water which will flow out of a tank depends upon how wide the valve is opened. Motors connected to such circuits regulate themselves by cutting off the current when the speed of the motor has reached the proper limit.

Among motors of this kind are the Sprague, Thomson-Houston, C. & C., and others. In the series system a definite amount of current is forced through the wire, and the amount of electric power absorbed is regulated by forcing this definite current to do more or less work as it passes through. Motors operating on such circuits cannot regulate themselves by cutting off the current when sufficient speed is attained. In place of this a

number of devices have been made for the purpose of regulating motors on these circuits. One arrangement for this purpose is that employed in the Crocker-Wheeler motor. It consists of a gramme ring armature revolving in a stationary field magnet and provided with a governor attached to the shaft within the pulley of the machine. When the speed of the motor reaches the proper limit, the governor draws the armature lengthwise out of the field, thereby weakening the power, and keeping the machine running at constant speed under any variation of the work required of the motor. See the Electric Motor and its Applications, Martin and Wetzler; Dynamo-Electric Machines, S. P. Thompson.

ELECTRIC ORGAN. Electricity is used in two ways in operating organs-for pumping and for operating the valves leading to the various sounding tubes in accordance with the manipulations of the key-board. In many places, especially in large churches having complicated organs, a part of the organ tubes are at such distance from the key-board as to preclude the air being admitted to them and shut off quickly as is required in playing, by any mechanical means which can be actuated by the weak force with which the organist depresses the keys. To meet this difficulty, the agency of elec tricity has been invoked, and now in all large organs the connection from tubes to keyboard is made in this way: The valve admitting the air to the sounding tube is controlled by an electro-magnet. This magnet is connected by a wire to the key-board, and is led to a contact point on the under side of the key corresponding to this tube. The wire is also connected to a suitable battery which supplies the current when this key is depressed, and also supplies the wires leading from all the other keys to the other tubes. When the keys are depressed by the organist the magnets throw open the air valves, and the corresponding notes are sounded without effort of the operator. The application for pumping air for organs is made by the use of an ordinary electric motor (q.v.), the motor being connected to an electric light circuit to draw its supply of clectricity and geared to the bellows of the organ, so as to operate the latter.

ELECTRIC RAILWAYS. One of the most important applications of electricity, and the most important of its applications to the transmission of power, is its use for propelling cars. This use is being rapidly developed at present. The value of the plan depends upon the fact that large amounts of power, after being converted into electricity, may be carried through the rails of the track or through convenient conductors overhead to the moving cars, and there readily converted without trouble into the power necessary for driving the cars. This conversion is effected through the agency of electric motors (q.v.), which are small, clean, noiseless, and easily handled, and are therefore to be preferred to either dummy engines or horses. The generation of electricity at the central station and its reconversion of power at the car can be accomplished with the loss of less than 40 per cent. of the power supplied at the station. So the system of carrying the power to the car is sufficiently efficient to permit of great saving by generating all of the power at one place by a very good engine instead of by a number of poorer and less efficient engines on the cars, which are invariably several times more expensive, or by the use of horses, which are still more expensive. The full-page illustration shows a station fitted with Edison dynamos (see MAGNETO-ELECTRIC MACHINES) driven by high-speed Armington and Sims engines. It may be mentioned that the station illustrated is also adapted to supplying electric lights. The current generated at this station is led out to the cars by suitable conductors. In the particular place chosen as an illustration-the city of Richmond, Va.-where the entire street-car lines of the city are run by electricity, the cur rents are carried out from the station upon overhead conductors. These conductors are run parallel with the tracks, and are suspended a few feet above the cars. The connection from the conductor to the motor in the car is made by a flexible arm projecting up from the top of the car, very much like a fishing pole, carrying on its end a roller or trolley which presses upward against the conductor. The current passes from the conductor to this roller, and down the rod to the roof of the car; thence by a wire to the motor and to the car wheels, and returns by the rails to the station. The motor is connected by suitable gearing to the wheels of the car. The speed of the car is regulated by proper controlling switches governing the power of the motor. The introduction of electric motors for running street cars has progressed very rapidly.

ELECTRO-CAUTERY. By means of a heated platinum wire, parts of the body may be safely cauterized which could not be reached by a red-hot iron. The removal of tumors may be effected by drawing a loop of platinum wire round their base, which is then gradually pulled together. It has been observed that when the temperature of the wire is about 600° C., the combustion of the tissues is so complete that there is no hemorrhage; while at 1500° the action of the wire is like that of a sharp knife.

ELECTRO-CHEMICAL ORDER OF THE ELEMENTS. When two metals are placed in contact and immersed in a solution capable of acting on one of them, an electric current is produced, positive electricity passing from the metal acted on, through the liquid, to the metal unacted on. The former metal is said to be electro-positive to the latter. By experimenting with different pairs, we can arrange the metals in electro-chemical order. This order depends upon the readiness with which the metals are acted upon by the solution, and is not the same for all solutions.

The following is the electro-chemical order of the more common metals, the liquid