Page:Popular Science Monthly Volume 5.djvu/742

722 with which it was measured, is considered, this is not a favorable exhibit. An advantage, nevertheless, which the electric light very distinctly possessed over the other, was in its creating a kind of glow in the fog, by which mariners were enabled to recognize the position of the capes even when both lights were invisible. Experiments were made with the view of ascertaining, with some approach to accuracy, the relative fog-penetrating power of the two descriptions of light produced by electricity and by ordinary combustion, when the photometric intensities are equal; and also the excess of intensity which must be given to the former light, in order that its power in this respect may be equal to that of a lamp fed by oil. In these experiments it was attempted to imitate, as nearly as possible, the absorbent effect of fogs, by interposing glasses of different colors—red, orange, yellow, etc.—before each of the lights successively. The conclusion which these experiments seem to justify is, that, whenever an electric light exceeds in intensity a light produced by a lamp two and a half times, it will penetrate, at least as well as the latter, the fogs most unfavorable to the transmission of the rays. And, as a fact, in whatever state of the weather, the electric light at La Hève has always had the largest range of visibility" ("Reports of the United States Commissioners to the Paris Exposition, 1867," vol. iii.).

M. Becquerel, in an article on electrical apparatus exhibited in the Exposition of 1862, enters into a calculation of the cost of the electric light, compared with other methods of illumination. His estimates are based upon a light produced by a magneto-electric engine, driven by an engine of two horse-power, which light he calculated was equivalent to that produced by 700 stearine-candles. He compares the light thus obtained with that obtained of equal intensity from the galvanic battery—from coal-gas, oil of colza, tallow, stearine, and wax. "The price of gas taken was $30⁄100$ of a franc per cubic metre—equivalent to 17 cents per 100 cubic feet; oil of colza, $1.28 per gallon; tallow, in the form of candles, 16 cents; stearine, 36 cents; and wax, 52 cents per pound." The cost of the electric light he assumes to be only that of the combustibles required to run the engine. From these data he deduces the following values:

A light equal to that of 700 stearine-candles will cost per hour:

"In point of cheapness there would seem to be no comparison between the electric light and that produced by even the least costly of