OF ARTS AND SCIENCES. 



203 



received by the condenser by Q, the electro-motive force and the 

 Civpacity of the condenser by E and C, we have Q = EG. We also 



have Q^z"^ sin .V qp, where n is tlie reduction factor of the galva- 



noraeter, t the time of vibration of tiie magnet, and (p the arc through 

 which it swings under tlie effect of tlie charge. Knowing the re(bic- 

 tion factor of my galvanometer, I had thus the means of reducing my 

 re.<ults to absolute measure. But I speedily found that the relative 

 results obtained by the proportions 



Q: Q' = sin ^ (f : sm ^ cp' = E : E' 



would present the points of this investigation in a manner as valuable 

 as if the results had been reduced to absolute magnetic measure. 

 My first experiments were made with solid armatures. 



TABLE I. 



In this table, the numbers are the deflections of the reflecting gal- 

 vanometer expressed in millimetres. In this case, tlie gain by the use 

 of the armatures was trifling, being only about 14 per cent. These 

 results were obtained by charging the condenser of ^ of a Farad, by 

 sparks one millimetre in length. 



On a closed secondary circuit, however, a gain of one hundred per 

 cent was clearly shown in the strength of the induced current pro- 

 duced by breaking the primary circuit. The question of how to make 

 this great increase in the strength of the induced current by the 

 employment of armatures manifest in the spark became an interesting 

 one. It seemed at first as if the application of armatures, by maintain- 

 ing the temporary magnetization of the iron cores, would be detrimental 

 rather than otherwise. 



I next tried the effect of bundles of thin iron plates, which were 



