722 THE POPULAR SCIENCE MONTHLY. 



with which it was measured, is considered, tliis is not a favorable ex- 

 hibit. An advantage, nevertheless, which the electric light very dis- 

 tinctly 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 pro- 

 duced by electricity and by ordinary combustion, when the photo- 

 metric intensities are equal ; and also the excess of intensity which 

 must be given to the former light, in order that its power in this re- 

 spect 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, yel- 

 low, 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 un- 

 favorable to the transmission of the rays. And, as a fact, in whatever 

 state of the weather, the electric light at La Heve has always had the 

 largest range of visibility " (" Reports of the United States Commis- 

 sioners 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 equiv- 

 alent 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 -f^-^ of a franc per cubic metre — 

 equivalent to 17 cents per 100 cubic feet; oil of colza, $1.28 per gal- 

 lon; 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 : 



1 produced by the Machine 2 to 4 cents. 



2 " " Galvanic battery 38 to 94 cents. 



3 " '« Coal-gas 62 cents. 



4 " " Kerosene 73 cents. 



5 " " Pure oil of Colza $1.14 



6 " " Tallow-candles 2.37 



7 " " Stearine 5.00 



8 " " Wax 6.10 



" In point of cheapness there would seem to be no comparison be- 

 tween the electric light and that produced by even the least costly of 



