106 ANNUAL OF SCIENTIFIC DISCOVERY. 



sition to the bright light of incandescence, the less strongly luminous electric 

 light disappears in the same way as the weak, bluish, lower part in a gas- 

 flame appears black in opposition to the bright mass of light, whilst with the 

 small brilliancy of a wax-light, the latter betrays its color even without optical 

 aids of absorption. Only prismatic analysis, and the action upon uranium 

 glass, indicate the presence of the electric light also. If the particles at a 

 white heat do not reach each other, the spark acquires a spot of interruption, 

 which, however, still shows red light besides the true electric light, when the 

 particles previously at a white heat have become cooled to redness. The 

 basal point of the brush, which retrogrades in proportion to the larger field 

 in which the electric light becomes visible, is to be compared with the spot 

 of interruption of the spark ; the particles of the solid body which are here 

 still red-hot may, on reaching a greater distance, be completely extinguished, 

 so that then the electric light alone prevails. The brush could not be colored 

 by a spirit-flame colored yellow with chloride of sodium held under it, as it 

 then becomes converted into a spark. The phenomena of the exhausted 

 tube with mercury, indicate the modification which the electric light under- 

 goes in media other than atmospheric air. Phil. Mag . 



ELECTRO-MOTIVE FORCE OF VARIOUS BATTERIES. 



M. Petruscheski, a Russian experimenter, gives the following as the 

 results of his investigations on the power of different voltaic combinations : 



Grove, with amalgamated zinc, 1.78 



Battery of cast iron and amalgamated zinc, 1.72 



Bunseii, 1 69 



Eisenlohr (Daniell's, with tartrate of potassa in place of sulphuric acid), 1.05 



Darnell, with chloride of sodium, 1.05 



" chloride of sodium and amalgamated zinc, 1.01 



" with dilute sulphuric acid, 1.00 



Eisenlohr, with zinc not amalgamated, 0.99 



Daniell, dilute sulphuric acid and amalgamated zinc, 0.93 



Wollastou, with amalgamated zinc, 0.93 



Cosmos, vol. xli., p. 4. 



COST OF ELECTRIC LIGHT. 



M. Edmond Becquerel has been recently engaged in some experiments 

 with a view to determine the comparative cost of electricity as an illuminat- 

 ing agent. He used a battery of zinc and platinum, made with strict atten- 

 tion to economy, and the results were as follows : 



The standard is the light of 350 candles of the best quality, and the com- 

 parative cost of 



Coal gas at SI 60 per 1000 c. feet, was $0 35 



Oil (Rape Seed), at 17 cents per pound, 60 



Stearine candles, at 32 cents per pound, 252 



Wax candles, at 52 cents per pound, 3 12 



Electric light, 58 



Thus showing that, although the electric light is cheaper than candles, it 

 will not at present compete with coal gas, at least until some cheaper battery 

 power be found. 



