INORGANIC RESPONSE 



whether the E.M. effect of mechanical stimulus is in- 

 stantaneous, or, again, whether the effect disappears 

 immediately. We first take a galvanometer record of 

 the sudden introduction and cessation of an E.M.F. on 

 the circuit containing the vibration-cell (fig. 60, a). 

 We then take a record of the E.M. effect produced by 

 a stimulus caused by a single torsional yibration. In 

 order to make the conditions of the two experiments 

 as similar as possible, the disturbing E.M.F., from 

 a potentiometer, is pre- 

 viously adjusted to give a 

 deflection nearly equal to 

 that caused by 



60 



(a) Arrangement for applying a short-lived E.M.P. 



(b) Difference in the periods of recovery: (1) from instantaneous E.M.F. ; 



and (2) that caused by mechanical stimulus. 



The torsional vibration was accomplished in a quarter 

 of a second, and the contact with the potentiometer 

 circuit was also made for the same length of time. 



The record was then taken as follows. The record- 

 ing drum had a fast speed of six inches in a minute, 

 one of the small subdivisions representing a second. 

 The battery contact in the main potentiometer circuit 

 was made for a quarter of a second as just mentioned 

 and a record taken of the effect of a short-lived E.M.F. 



