332 Messrs. Trowbridge and Sabine on 



The difference in the time of oscillations cannot be ex- 

 plained by the vibration of the discharging arm lengthening 

 and shortening the sparking distance, since this would ne- 

 cessitate a vibration frequency of 100,000 per second, and an 









Fig. 5. 

























V, 





































Fi£ 



>.e. 

























































amplitude of at least one millimetre : a velocity and momen- 

 tum impossible for the apparatus either to acquire or endure. 

 This cause also would tend to make the variation range 

 equally above and below the calculated value as the sparking 

 distance increased or diminished. 



Another explanation may be sought in the varying ohmic 

 resistance of the path of the spark, although this explanation 

 is inadequate to explain the whole effect. Jn order to test it, 

 a long (1"3 centim.) and short (*4 centirn.) spark were taken 

 from a glass Leyden-jar (see fig. 7). Not only could no 

 appreciable difference between the two plates be detected, but 

 there was no variation in the time of successive oscillations. 



In regard to the measurement of the negatives on the 

 dividing-engine, the following points may be worthy of 

 mention. At the time the measurements were made, it was 

 expected that the sparks from the glass condenser would show 

 the variations, and that the air condenser would give the 

 constant and theoretical period of oscillation. The. reverse 

 of this appeared when the results of the measurements were 

 reduced. Moreover, the measurements were made by a run 

 of the dividing-engine from one end of the negative to the 



