loNIZATION BY NEGATIVE IONS 



85 



negative electrode; beyond this it holds, so that the 

 factor by which the current is multiplied by increasing 

 the distance from l\ to 1% is given accurately by 



Xfo-li) 



the term e v e t and this result is confirmed by 

 experiment. The potential difference between the 

 plates when the first distance l\ is used should 

 not be less than V, or li should be greater than 

 V/X, and for the larger distances the potential X 

 should not approach the sparking potentials, other- 

 wise the effects produced by positive ions would be 

 appreciable. 



Table XI. gives the values of V and NV for the different 

 gases. 



TABLE XI. 



The greatest conductivity is obtained with a force X 



X 

 when the pressure in millimetres P=^, X being 



expressed in volts per centimetre. For air this theory 



X 

 gives P=5^K which is in good agreement with Stoletow's 



ODO 



result P=^. 



The maximum value of a is ^y, or =^y, v, the 



potential difference between the plates, being expressed 

 in volts, and I in centimetres. 



D 2 



