Wellisch — Motion of Ions and Electrons through Gases. 5 



Yj, Y2 and R. This was effected by means of formula (1) 

 which for the purpose was put in the following form : — 



— Y^-\~c (say). 



r\\ 



(2: 



-y was always chosen equal to 40 volts and r was always 15,000 

 ohms. The calculated values of g for various values of p and 

 Yi + Y2 were then tabulated and the value of x under any 

 desired conditions could be quickly obtained. 



Establishment of Potential. 



It was important to ascertain that the experimental con- 

 ditions admitted of an effectively instantaneous establishment 



Fig. 3. 



ky^^M 



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▼ TO CAUZE 



of the withdrawing potential —Y^ through the resistance 

 R ; in other words, the ions must commence to retire as 

 soon as the commutator brushes make contact with the 

 fiber segments. This point was tested experimentally in the 

 following manner : the commutator and resistance E- were 

 put in series with a battery Y (fig. 3) of which one terminal 

 was earthed ; K represents a Kelvin multicellular electrostatic 

 voltmeter which was included in the manner shown in the dia- 

 gram. The commutator was set in motion at its highest speed 

 and readings were taken on the voltmeter corresponding to 

 different values of R. If the values of R were excessively 

 large there would not be sufficient time during an alternation 

 to admit of the earth connection with the gauze being fully 

 established and in consequence the steady reading of the volt- 

 meter would be too large. It was found that when the small 

 frequency comutator was employed this steady reading remained 

 constant for values of R up to 1,000,000 ohms ; for the high 



