Page:Popular Science Monthly Volume 11.djvu/447

Rh sufficient to melt and even to vaporize glass or kaolin, and thus the insulating septum between the carbons wears away simultaneously with them.

If the source of electricity gives constant currents, then, inasmuch as the carbons wear unequally, one wasting more rapidly than the other, the distance between the points will become too great, and the light will be extinguished. To overcome this difficulty, we have only to make the carbon that burns most rapidly twice as thick as the other.

It is true that hitherto the electric candle has worked better with magneto-electric machines giving alternating currents, than with piles or Gramme machines; in the former case the carbons wear away equally, and are of the same thickness.

To complete the description of Jabloshkoff's apparatus, we have to add that each carbon is socketed in a brass tube, connected with a wire coming from the source of electricity. These two tubes are attached to each other in various ways, according to the applications had in view; the one essential precaution is, to take care that they do not come into contact with each other.

The name candle has been very happily applied to this simple apparatus; it is, indeed, a candle with two wicks burning side by side, and which lower their luminous point as combustion goes on. One interesting peculiarity it possesses, namely, that the luminous point can be turned downward, so that there is nothing to throw a shadow. Its light may be modified by the use of opal or ground-glass shades.

—One of the principal advantages of Serrin's lamp is, that it can be lighted from a distance. The lamp is made ready, say, in the morning, and, when night comes, all that is required is to admit the