4 Wellisch — Motion of Ions and Electrons through Gases. 



worked generally on 110 volts which afforded approximately 

 42 revolutions per second. 



The double-pole, double-throw switch S, when thrown to the 

 right, completed the connections as exhibited graphically in 

 fig. 1. When thrown to the left, connection was made with a 

 subsidiary potentiometer system (b) ; in this position the quad- 

 rants of the electrometer could be com mutated in potential 

 between zero and any convenient potential read off on the poten- 



FiG. 2. 



tiometer. The use of this device in testins; the contact at the 

 brushes, in estimating the value of/*, the fractional duration of 

 contact, and in adjusting the position of the electrometer needle 

 for observations, has been described in the previous paper. 



For large current values readings were taken with the capaci- 

 ties B and C added to the electrometer system ; the capacity of 

 the system was then increased 17^- times. 



3. EXPEEIMENTAL PROCEDURE. 



For convenience in manipulation a table was prepared of the 

 potentials assumed by the gauze for different values of /o,. 



