CHAPTER VII.

THE ELECTRIC LIGHT.

VOLTAIC ARC BY SIR HUMPHREY DAVY--THE JABLOCHKOFF CANDLE--PATENTS OF BRUSH, WESTON AND OTHERS--SEARCH LIGHTS--GROVE’S FIRST INCANDESCENT LAMP--STARR-KING LAMP--MOSES FARMER LIGHTS FIRST DWELLING WITH ELECTRIC LAMPS--SAWYER-MAN LAMP--EDISON’S INCANDESCENT LAMP-- EDISON’S THREE-WIRE SYSTEM OF CIRCUITS--STATISTICS.

The popular idea of the electric light is, that it is a very recent invention, since even the younger generation remembers when there was no such thing in general use. It will surprise many readers, then, to know that the electric light had its birth in the first decade of the Nineteenth Century. In 1809 Sir Humphrey Davy discovered that when two pieces of charcoal, which formed the terminals of a powerful voltaic battery, were separated after having been brought into contact with each other, at the moment of separation a brilliant arc of flame passed from one piece of charcoal to the other, producing a temperature of 4,800° F., and that the intensity of the light exceeded all other known forms of light. Various improvements in the organization of devices were made for holding the two pieces of carbon, which in time assumed the form of two pencils in alignment, as in Fig. 40, and devices were provided for feeding one carbon toward the other as they burned away. Clock mechanism for thus regulating the feed was first employed, which served to automatically keep the carbons a definite distance apart, this being a necessary condition of the arc. For many years, however, the use of such a light was confined to laboratory illustration, for the reason that it could only be produced at great expense by a large number of voltaic batteries. Nevertheless very efficient electric lamps working by voltaic batteries were devised by Foucault, Duboscq, Deleuil and others as early as 1853. With the advent of the dynamo, however, the electric light grew rapidly and developed into conspicuous use. Even before the true dynamo was invented the magneto-electric machine was employed for producing an electric current to supply electric light. The so-called “Alliance” generator was, in 1858, used in the South Foreland lighthouse in England to supply the arc lamps, and the beams of the electric light then, for the first time, were turned seaward as a beacon for the mariner.

Among the early developments of the electric light was the Jablochkoff candle, see Fig. 41, brought out in 1877. In this device two parallel sticks of carbon G G were separated by a non-conducting layer of kaolin I, and were held in an asbestos ferrule A. Metal tubes T T connected the conducting wires F F to the carbons. The arc of flame passed from the top of one carbon to the other, fusing the separating layer of kaolin, and the whole burned down together as a candle. This form of electric light was extensively used in Paris in 1877, and also in London, and attracted considerable attention.

From the Jablochkoff candle the arc light has resumed the form of two vertically aligned carbons, and after passing through various forms and patterns, of which the Weston lamp, Fig. 42, is a modern type, has come into such universal and conspicuous use for lighting the streets of our cities, and is so well known to-day, that but little need be said of its development, since its real character has undergone no change in principle, the improvements relating chiefly to means for regulating the feed of the carbons and maintaining them at a uniform distance apart, so as to avoid flickering. This result is obtained by automatic mechanism operated by the electric current acting upon electro-magnets, as shown in Fig. 43, in which the electro-magnets raise the upper carbon when it is too close to the lower carbon, and lower the upper carbon when the space becomes too great from burning away. Among those who have contributed to the development of the arc light the names of Brush, Weston, and Thomson and Houston are most conspicuous, and the patents of Brush, No. 203,411, May 7, 1878, and No. 212,183, Feb. 11, 1879, and Weston, No. 285,451, Sept. 25, 1883, are the most representative developments.

The applications of the arc light have been brilliant beyond the dreams of the most sanguine inventor. In the illustrations number 44, 45 and 46, is shown a gigantic electric light beacon manufactured by Henry Lepaute, of Paris, and first exhibited in this country at the Chicago World’s Fair, in 1893. It consists of two great lenses, each nine feet in diameter, between which, in their focus, is placed a 9,000 candle power arc light. The great lantern, Fig. 45, is carried by a vertical shaft, which terminates at its lower end in a hollow drum, which latter floats in a bath of mercury. Although the weight is estimated at several tons, so sensitive is its poise on the mercury that the enormous lantern may be easily rotated by the pressure of one’s finger. Each lens consists of concentric segments, see Fig. 46, 190 in number, surrounding a central disk, which together cause the rays to issue in parallel lines. The nine-foot beam of light thus projected is of 90,000,000 candle power, and if placed at a sufficient altitude to avoid the curvature of the earth’s surface, its light would be visible at the range of 146.9 nautical miles.

Better known to the patrons of our excursion boats and the visitors to our splendid battleships, are the electric search lights. The greatest example of all search lights, however, is not to be found on the sea, but in the picturesque altitudes of the Sierra Madres in Southern California. At the summit of Mount Lowe, in the neighborhood of Pasadena, is the largest search light in the world, shown in illustration, Fig. 48. It is of 3,000,000 candle power, stands eleven feet high, and its total weight is 6,000 pounds. Its light may be seen for 150 miles out on the ocean, and as its powerful beam is thrown from mountain top to mountain top hundreds of miles apart, it adds the illumination of art to the sublimity of nature, and seems a fitting jewel to this lofty crown of Mother Earth.

Brilliant as is the arc lamp, far more in evidence is the incandescent lamp. The little glass bulb with its tiny thread of light we find everywhere. Popular opinion and the decision of the courts accord this invention to Thomas A. Edison. The evolution of the incandescent lamp is, however, interesting, and may be briefly sketched as follows:

In 1845 there appeared in the _Philosophical Magazine_ a description of what was probably the first incandescent electric light. It was devised in 1840 by William Robert Grove, the inventor of the Grove battery, and is illustrated in Fig. 49. It is stated that he experimented and read by it for hours. It was described as follows:

“A coil of platinum wire is attached to two copper wires, the lower parts of which, or those most distant from the platinum, are well varnished; these are fixed erect in a glass of distilled water, and another cylindrical glass, closed at the upper end, is inverted over them, so that its open mouth rests on the bottom of the former glass; the projecting ends of the copper wires are connected with a voltaic battery (two or three pairs of the nitric acid combination), and the ignited wire now gives a steady light. Instead of making the wires pass through the water, they may be fixed to metallic caps well luted to the necks of a glass globe.”

In 1845 August King patented, in England, an incandescent lamp, having an unsealed platinum burner, and also a carbon in a vacuum. Mr. King acted as agent for an American inventor, Mr. Starr, and the lamp came to be known as the Starr-King lamp, shown in Fig. 50. The burner was a thin plate or pencil of carbon B, enclosed in a Torricellian vacuum at the end of an inverted barometer tube, and held between the terminals of the connecting wires leading to a battery. In 1859 Moses G. Farmer lighted his house at Salem, Mass., by a series of subdivided electric lights, which was the first private dwelling lighted by electricity, and probably the first illustration of the feasibility of subdividing the electric current through a number of electric lamps.

In 1877 William E. Sawyer applied for a United States patent for an electric engineering and lighting system, and in January, 1878, entered into a partnership with Albon Man, and the “Sawyer-Man” lamp, see Fig. 51, was produced. In this an incandescent rod of carbon was inclosed in an atmosphere of nitrogen. This marked the beginning of a period of great activity in this field, which finally resulted in the well known form of electric lamp shown in Fig. 52, which was patented by Edison, No. 223,898, January 27, 1880. The distinctive features of this lamp consisted in a bowed filament of carbon of very thin, thread-like character, which was made of paper or carbonized cellulose. This, when sealed in a vacuum, would not burn away, but would give the proper incandescence, and by its small transverse dimension and high resistance to the current, permitted a proper distribution of the electric current to a number of lamps, without a special regulator for each lamp; and which could also be made so cheaply that the lamp could be thrown away when the burner was finally broken. Edison’s claim on this feature of the electric lamp was sharply contested in an interference in the Patent Office by Sawyer and Man, with the decisions alternating first in favor of one and then of the other, but which finally resulted in the grant of a patent to Sawyer and Man, on May 12, 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.

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.

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.