Oscillatory Discliarges. 631 



(b) Value adopted for Capacity of Condenser. 



34. The great care bestowed on the absolute measurements 

 of the capacity of the condenser, and the agreement of the 

 value thus obtained with the one resulting from a comparison 

 with the sample kindly forwarded by Prof. R6iti, entitle us 

 to maintain that the value obtained by us is trustworthy in 

 all respects. 



On the other hand, it might be suspected that for large 

 potential-differences between the armatures, as those corre- 

 sponding with the explosive distances of some millimetres 

 used by us, the charge should extend over the glass edges 

 not covered with tinfoil to a much higher degree than in the 

 case of the very slight charges used with the above-mentioned 

 standardizing, and that hence the true capacity is larger 

 than the one noted. Whether this is really the case, we were 

 not in a position to ascertain ; but it is certain that, if for 

 high potentials there occurs a greater diffusion of charge on 

 the glass, this could not augment practically the effective 

 capacity of the condenser, as at the moment of the spark 

 the electricity going on to the glass is not discharged in the 

 same way as that taken by the metallic armatures. 



One also might object that the capacity for rapidly oscil- 

 lating discharges should be different, even for air-condensers, 

 from that given by measurements with slow charges — in fact 

 this objection has been raised against Hertz's experiments. 



But applying to our experiments Drude's calculations 

 (Physik des JEthers, p. 459), one easily understands that no 

 correction is to be made on this account in the above- 

 mentioned value of the capacity used in our experiments. 



Moreover, as the total resistance of the circuit containing 

 the spark will subsequently be shown to be negligible as 



compared with ^rs — the reduced formula of Thomson thus 



applying to this case — from the striking agreement which in 

 this case also exists between the calculated and observed 

 periods, it may be inferred that the value adopted for the 

 capacity of our condenser, obtained from determinations 

 made with slow charges and low potentials, is really true 

 also for oscillatory discharges and for the potentials used 

 in our experiments. In addition, this agreement may be 

 regarded as an evidence that the dielectrical hysteresis of 

 the air is really negligible for the periods of the discharges 

 photographed by us. 



2 U2 



