392 



Dr. W. L. Robb on Oscillations 



charge which the condenser eventually assumes when charged 

 for a considerable time. These variations and their character 

 seemed to indicate that, during the charging of a condenser, 

 oscillations occurred in the charge. Any variation in the 

 velocity of the smaller sphere at the moment of contact would 

 vary the time of contact, and consequently the charge given 

 to the condenser. Owing to the character of the suspension 

 of the smaller sphere it was found that, even when the greatest 

 care possible was taken, slight variations in the time of contact 

 would occur. 



If the relation between the charge of a condenser and the 

 time of charging were represented by a curve such as that 

 given in fig. 2 (see Table XL), owing to the variation in the 



time of contact of the spheres that always occurs in a series 

 of observations, a series of determinations would give us, not 

 the charge corresponding to any single definite time, but the 

 charges corresponding to a series of different times comprised 

 between limits a and b, a denoting the shortest and b the 

 longest time of contact. Further, the greatest difference in 

 the charges observed would be an indication of the amplitude 

 of the oscillations corresponding to the time of contact. 



The following analytical consideration of the charging of a 

 condenser shows that oscillations in tlie charge should occur ; 

 and indicates how the oscillations are related to the time of 

 charging, the resistance and self-induction of the circuit, the 

 electromotive force of the charging battery, and to the 

 capacity of the condenser. 



In fig. 3 let i denote the current in the circuit, and P x and 

 P 2 the potentials of the two surfaces of the condenser at any 

 time / after the closing of the circuit. Then, if C be the 

 capacity of the condenser, E the electromotive force of the 



