54 



THE ROYAL SOCIETY OF CANADA 



If practical electromagnetic units be used the mobility is given by 



k=32 



d'.i. 10". 



cm. a sec. per volt a cm. (2) 



where i is expressed in amperes, V is in volts and d in cms. 



If c be the capacity in E.S.U. of the electrode AB together with 

 the leading wires, quadrants and attached condensers to which it 

 is connected; r the radius of the opening in the ebonite plate EF, x 

 the number of scale divisions which correspond to a potential of 1 

 volt applied to the quadrants and y the number of scale divisions 

 per min. corresponding to the current between the two electrodes 

 for a given applied field, then i in equation 1 is given by 



1 = 



and therefore 



k = 



32 



_. X 

 9 . 10" 60. r 



d' 



irr 



V2 



10" • 



amperes 



yc 



r' . X • 60 • 9 • 10' 



_ 8 d^ ' y ' c ^ 

 ~135 Y- • /-. x' 



Since with the apparatus used d = 1 em. and r = 53 cm. it follows 

 that k is given by 



X V^ 



For a selected pressure this relation shews that y should be pro- 

 portional to V-' 



TABLE VL 

 No. of scale divisions per volt=x=40() 



