Bowling — Sensitive Valve Method for Measurement of Capacity. 177 



of the dielectric between the condenser-plates, or to movements of the latter 

 relative to one another. It is principally in the latter connexion that the 

 device has its widest field of application ; and I shall give in this paper a brief 

 account of some preliminary work done in that direction. 



I may say, at the outset, that I have not yet tried to push the apparatus, 

 even in its present form, to the highest possible sensitivity, but have aimed 

 rather at determining the sensitiveness obtainable under ordinary working 

 conditions. As is well known, in developing an apparatus of high sensitivity, in 

 proportion to the augmentation in sensitiveness, unsteadiness and variability 

 of the readings become more pronounced. To derive the fullest measure of 



Fig. 2. 



performance from such apparatus, a great amount of attention and care has 

 to be devoted to the perfection of its parts, and the elimination of small 

 disturbing influences. Even without such special precautions, the performance 

 of the present apparatus has been remarkably good. 



II. — Experimeyits with Condensers. 



In the greater number of tests to be described, the valve, an Ediswan 

 E. S. 1. type receiving valve, was operated with 50 volts in the plate- 

 circuit, the filament being heated by a four-volt accumulator, the negative 



2d2 



