176 



Scientific Proceedings, Royal Dublin Society. 



still a considerable current indicated by the milanimeter. In order to obtain 

 a sensitive arrangement it is necessary to balance this " zero current " by an 

 opposite steady current. We may then substitute a sensitive galvanometer 

 for the milammeter, with the result that small capacities can be measured. 



-4t 



O 



^S 



VOL TS. 



Fig. 1. 



By an obvious extension of the same principle, if we balance the greater 

 part of the plate-current, due to a rather large capacity in the grid-potential 

 circuit, it becomes possible to make very accurate comparisons between two 

 condensers of nearly equal capacity, or to study slight variations in the 

 capacity of a given condenser. Such variations may be caused by alteration 



