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.
FIG. 43.—ARC LAMP FEED MECHANISM.
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.
FIG. 44.—NINE THOUSAND CANDLE POWER ARC LAMP.
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.