Page:Popular Science Monthly Volume 11.djvu/448

432 current, and light is instantaneously produced. At first Jabloshkoff lighted his candle directly by supporting on the tips of the two wicks a piece of charcoal which he soon afterward removed; thus the voltaic arc was produced as in electric lamps, by beginning with contact, and then placing the two carbons at the required distance from each other. But it was necessary to devise some method for lighting the candle from a distance, and this fresh difficulty M. Jabloshkoff has overcome by a very simple device. He places between the two carbons a little bit of graphite, of the diameter used in lead-pencils; this acts as a conductor between the two wicks of the candle. On the current entering it, the bit of graphite soon becomes red-hot, and is burned up; there is then a break of continuity between the wicks, and the electric arc is produced. Instead of graphite, a fine metallic wire, or a bit of lead, can be used.

—As we have stated, the insulating strip between the wicks is fused at the points near the voltaic arc, and so disappears gradually in proportion to the waste of the carbon-points. But this fusion of the insulator is attended with another consequence that but few of our readers would have anticipated. That which in its solid state is an insulator becomes in its liquid state a conductor, and allows of a longer span of the electric arc than could be had in the free air. Owing to this conductivity of the strip of kaolin, the circuit may be opened for a moment and the candle lighted again without any need of resorting to any of the contrivances already described under the head of "Lighting." But after a certain length of time, as the substance cools, it loses its conductivity, and then the candle cannot be relighted by simply closing the circuit again. We may extinguish the candle for nearly two seconds, and relight it by simply closing the circuit. Hence the electric candle may be used for transmitting telegraphic signals according to the Morse alphabet, by means of flashes of greater or less duration, divided by longer or shorter periods of eclipse. For such use the candle is better adapted than the electric lamp, as it is more readily relighted, producing at once a perfect voltaic arc, whereas in the lamp the arc is produced gradually.

—Hitherto a separate pile, or a separate machine, has been necessary for the production of each electric light, and it has been found impossible to place two lamps in one circuit. This is readily understood when we consider the mechanism of the regulating apparatus. In electric lamps the approximation and the separating of tlie carbons are controlled by an electro-magnet, which itself follows the variations of resistance in the circuit produced by changes in the length of the voltaic arc. As the arc lengthens the resistance of the circuit is increased, and the electro-magnet is weakened, and allows the carbons to approximate. It is easily understood that if there are two lamps and two voltaic arcs in one circuit, and if only one of these arcs is lengthened, both electro-magnets will act and