1885. A struggle then began in the courts, which on October 4, 1892,

terminated in a decision by the United States Court of Appeals (Edison Electric Light Company vs. United States Lighting Company), awarding the incandescent lamp to Edison. [Illustration: FIG. 51.--SAWYER-MAN LAMP.] [Illustration: FIG. 52.--EDISON’S ELECTRIC LAMP. _A_--Exhausted globe. _B_--Carbon filament. _CC_--Wires sealed in glass. _D_--Line of fusion of two parts of globe. _EF_--Insulating material. _G_--Screw-threads. _HI_--Metal socket. _J_--Fixture arm _K_--Circuit controlling key.] In the early demonstration given by Edison great disturbance was caused in the stock exchanges among the holders of gas shares, as the sensational reportings in the press seemed to indicate that gas was to be superseded entirely. This uneasiness on the London Stock Exchange amounted on October 11, 1878, to a veritable panic, but while the electric light has more than fulfilled the prophecy made for it in many directions, gas shares still continue to be good stocks. [Illustration: FIG. 53.--ELECTRIC LIGHT CIRCUIT.] [Illustration: FIG. 54.--EDISON’S THREE WIRE SYSTEM OF ELECTRIC LIGHT CIRCUITS.] Closely allied to the practical use of the incandescent lamp is the method of supplying and regulating the current from the dynamo. Although the alternating current is used for arc light, only the continuous current can be used for the incandescent lights, and the relation of the dynamo and the incandescent lamps is shown in Fig. 53, in which L represents the lamps between the main conducting wires leading from the dynamo, which latter has the coils of the field magnets arranged in a shunt or branch circuit, in which is interposed a regulator R in the form of a resistance coil with movable switch lever, by which more or less of the current is allowed to flow through the field magnet coils to suit the work being done. In late years automatic regulators have been provided for accomplishing this result. In Fig. 54 is shown what is known as the Edison “three wire system,” patented March 20, 1883, No. 274,290. In this two dynamos are used as at D¹ D², and the three wires emerge from the dynamos, one from the negative pole of one dynamo, another from the positive pole of the other dynamo, and the third or middle one is connected to both the other poles (positive and negative), of the two dynamos. For purposes of illustration, this may be compared to a three-storied arrangement of current, the upper wire representing the third story, the middle wire the second story, and the bottom one the first story. The fall from either story to the next represents the working energy, but from the top wire to the bottom would be equal to a fall from the third story to the first. The purpose of this arrangement is to save expense in copper wire, for while three main wires are used instead of two, the aggregate weight of the wires (when the lamps are arranged as shown), may be made so much less than two heavy wires as to make a very great saving in copper. The uses of the incandescent light are legion. Besides those which are of common observation it is used for lighting the interior of mines, caves, and the dark apartments of ships, and does not foul the air. It is also used by divers in submarine operations; in the formation of advertising signs, and in pyrotechnics, but perhaps one of the most extraordinary uses to which it has been put is in exploring the interior of the human stomach and other cavities of the body, a patent for which was granted to M. C. F. Nitze, No. 218,055, July 29, 1879. When an electric lamp is arranged with the opposite ends of the carbon burner connected, one to the outgoing, the other to the incoming wires from a dynamo, so as to be bridged across, this arrangement is said to be “in multiple” or “in parallel,” and the lamps bear the analogy of horses drawing abreast, and when the opposite ends of the carbon burner are placed in a gap or break in either the outgoing or the incoming wire, the arrangement is said to be “in series,” and the lamps bear the analogy of horses in tandem. Explanation of electric nomenclature can best be given by the analogy in hydrostatics of a stream of water passing in the hose pipe from a fire-engine. The “watt” indicates the sum total unit of electrical power for a definite period of time, and in the hose pipe would be represented by the effective force of a definite volume of water, passing at a definite pressure, during a definite period of time. “Volt” is a pressure unit of electro-motive force, and would be represented by the power of the engine. “Ampere” would be the quantity, or volume unit, or cross section of the hose pipe, and the “ohm” would be the unit of frictional resistance. The “watt” then would be the “volt” multiplied by the “ampere”; thus 500 watts would be 10 amperes at 50 volts, or 50 amperes at 10 volts. Low tension circuits, such as are used for incandescent lights, range from 100 to 240 volts and are harmless. Trolley circuits are usually 500 volts, and will kill an animal, but are not necessarily fatal to man. High tension currents from 2,000 to 5,000 volts, such as are used for arc lights, are fatal. Of all modern inventions, not one has advertised itself in such a spectacular way as the electric light. Those who have seen the magnificent electrical displays at the Chicago Fair, the electrical celebrations in New York, and the Omaha Exhibition, need no introduction to its marvelous splendors and beauties. In the annual report for 1898 of the Edison Electric Illuminating Company of New York, its statement shows that for that city alone the gross earnings were $2,898,021. There were 9,990 users of the electric light, 443,074 incandescent lamps, and 7,353 arc lights. It is estimated that the electric light stations and plants in the United States alone amount to $600,000,000. In the year 1899 a single manufacturing concern (The General Electric Company) received orders for 10,000,000 incandescent lamps, which is about one-half of the present annual production. Sixteen years ago the lamps were $1 each; to-day they can be bought for 18 cents. What the future has in store for the further development of the electric light no one may dare predict. Already a different form or manifestation of electric light has been demonstrated, in which neither the electric arc nor the incandescent filament is used, but a peculiar glow is seen disassociated from a direct material habitation, and produced by currents of enormous frequency and high potential, in accordance with the patent to Tesla, No. 454,622, June 23, 1891. Other worthy inventors in this field are at work, and its development will be one of the interesting problems of the Twentieth Century.