OF ELECTRO-DYNAMIC FORCES. 505 



necessary for ascertaining this proportion could not all be effected 

 with the requisite accuracy, because separate measures were not 

 taken for this purpose. In fact, however, the above factor was 

 provisionally, as well as circumstances permitted, determined by 

 direct measurement, and found =49-5. This result also exhibits 

 an agreement with that previously deduced from the observa- 

 tions, which under the circumstances could not have been ex- 

 pected to be greater. 



Observations tending to enlarge the domain of 

 Electro-dynamic investigations. 



A. Observation of Voltaic Induction. 



If the bifilarly-suspended coil of the dynamometer be made 

 to oscillate whilst a current is transmitted through it, or through 

 the coil of the multiplier, or through both simultaneously, this 

 motion is inductive, and excites a current in the conductor, 

 through which no current was passing, or alters the current 

 passing through this conductor. This mode of excitation of the 

 current is called voltaic induction. The inducing motion, i. e. the 

 velocity of the oscillating coil, is on each occasion diminished or 

 checked by the antagonism of the currents excited by the voltaic 

 induction and those conducted through the coil. This check 

 to the vibrating coil effected by the voltaic induction may be ac- 

 curately observed ; and at the same time the motion of the oscil- 

 lating coil itself, which produces the voltaic induction, may be 

 accurately determined ; and this twofold use of the dynamometer 

 affords the data necessary for the more accurate investigation of 

 the laws of voltaic induction. 



The bifilarly-suspended coil closed in itself was made to 

 oscillate to the greatest extent at which the scale permitted ob- 

 servations to be made, and its oscillations from were counted 

 until they became too minute for accurate observation. During 

 the counting, the magnitude of the arc of oscillation was 

 measured from time to time. These experiments "K^ve first made 

 under the influence of voltaic induction, a current from three 

 Grove's elements being conducted through the multiplying coil ; 

 the same experiments were next repeated, after the removal of 

 the elements, without voltaic induction : — 



vol. v. part XX. 2 M 



