Conductivity of Air enclosed in Metallic Receivers. 299 



the system acquired through the conductivity of the air in 

 the receiver ; this motion being so regulated as to keep the 

 potential of the gold-leaf always at zero, and thus minimise 

 any tendency to promote a leak across the quartz insulation. 



Thus for a determination of " q " it was necessary only to 

 know the charge annulled in the time during which the 

 compensator moved a standard distance. 



Fis. 2. 



For a determination of the charge corresponding to this 

 standard distance the parallel plate condenser shown in fig. 2 

 was added in place of the electrode. The compensator tube 

 was then charged to a known potential giving for the total 

 motion a certain deflexion of the gold-leaf ; and the voltage 

 on the upper condenser plate was then so adjusted as to 

 bring the gold-leaf back to its zero position. The charge 

 could then be readily calculated from the dimensions of the 

 parallel plate condenser and the voltage applied to it. 



The corresponding values of voltage on compensator tube 

 and charge annulled are given in Table II., and are illustrated 

 by the curve in tig. 3 (PI. V.). 



These values were determined experimentally, and they 

 showed that the capacity of the tube-condenser was, as its 

 construction demanded, practically independent of the voltage 

 applied to it. 



Table II. 



Voltage on 

 Compensator = V. 



Charge 

 Annulled = E. 



E/V. 





Electrostatic 



Units. 



Charge (E.S.U.) 

 per volt. 



28-4 



•1449 



00512 



367 



•1858 



•00506 



429 



•2146 



•00500 



51-1 



•2577 



•00504 



57-2 



•2853 



•00499 



654 



•3241 



•00495 



71-4 



•3528 



•00494 



78-3 



•3882 



•00496 

 Mean =-00501 



