30 Prof. G. Quincke on Electrical Expansion. 



mechanical energy must be applied to the driving-pulley of 

 the electric generator. If the loss so encountered was 40 per 

 cent., as appears to be the case with some of the best machines 

 which have been measured accurately, this would reduce the 

 light developed to 72 candle-power for each horse-power of 

 mechanical energy applied to the driving-pulley of the electric 

 generator. 



When we remember that with the arc-light there has been 

 obtained from 1200 to 1800 candle-power per horse-power of 

 mechanical energy applied to the generator, it is evident that 

 Mr. Edison's lamp as now made does not escape the enormous 

 loss which has heretofore been encountered by all forms of 

 incandescent electric lamps. 



IVj. On Electrical Expansion, By Dr. G. Quincke, Professor 

 of Physics in the University of Heidelberg*, 



AN extensive research on the action of electricity upon 

 bodies which conduct badly has given the following 

 results: — 



1. Solid and liquid bodies suffer change of volume when 

 they are exposed to the action of electric force in the same 

 way as the glass of a Ley den jar. 



2. This change of volume is not caused by change of tem- 

 perature ; generally it is an expansion ; but with a few sub- 

 stances, for example with the fatty oils, contraction takes place. 



3. No change was observed in the case of air exposed to 

 electric force. If any change of volume occurs, it must be 

 less than 30 o oo oo o~oo °f ^ ne original volume. 



Alteration of Volume under the Influence of Electricity. 



4. The electric expansion of glass is most conveniently ob- 

 served with a common thermometer, according to the method 

 employed by Fontanaf, GoviJ, and Duter§. The thermo- 

 meter was placed in a metal vessel filled with melting ice ; 

 the liquid inside the thermometer (water, mercury, or saline 

 solutions) formed the inner, the melting ice formed the outer 

 coating of a Leyden jar. 



When the two coatings of such a thermometer condenser 

 are placed in communication with an electrical machine 

 charged to a definite amount, or with a larger Leyden jar, the 

 liquid in the tube of the thermometer falls. The level of the 



* Translated from the Berichte der konigl. Akademie der Wissenschaften 

 of Berlin, of Feb. 19th, 1880. 



t Lettere inedite di Alessandro Volta (Pesaro, 1834), p. 15. 



\ N. dm. xxi.-xxii. p. 18 (1865-66). C. R. lxxxvii. 1878, p. 857. 



§ C. JR. lxxxvii. 1878, p. 828. . . 



