84 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



as soon as it could be obtained. The absence of electric current V" a = o 

 in the new instrument and its presence in the old electrometer made it 

 necessary to overhaul the latter. It was eventually found that the brass 

 case had been insufficiently earthed,* so that a current from the Zamboni 

 cell, breaking through the hard rubber insulation at the top of the quartz- 

 fiber suspension kept the case charged to a high-constant potential. 

 This charge thereupon gradually leaked into the insulated quadrant 

 through the amber insulators, producing the current V a corresponding 

 to the sign of the electrode of the Zamboni pile and of the electrometer 

 needle. On providing the case of the old electrometer with a well-earthed 

 clamp, the current V a vanished. The new electrometer did not show this 

 defect even when the case was not specially earthed, whereas any insu- 

 lation of the old electrometer immediately restored V a . 



Fortunately, however, V a is so remarkably constant that it can 

 actually be used in the measurements with advantage, as was done in the 

 present chapter, or eliminated by commutation, as was done in Chapter V. 



*Probably owing to a thin film of varnish which had escaped detection. The room 

 was so dry that no discharge occurred through the feet of the instrument. 



