in Gases at Low Pre* 



ssures. 



799 



The curves showing the relation between the pressure and 

 the product of the pressure and mobility for the various 

 gases are shown in fig. 6. It will be noticed that the 

 pressure at which the product begins to increase rapidly is 

 approximately inversely as the density of the gas. 



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The values for the mobilities at the higher pressures are 

 practically the same as for the ions produced by X-rays, 

 indicating that the particles which are ejected by the 

 aluminium phosphate transfer their charges on collision to 

 the gas molecules. In the author's previous paper on this 

 subject the product of the pressure and mobility for hydrogen 

 was rather low, and did not increase in the same region of 

 pressure as it has been found to do in the present experi- 

 ments. This was due to the fact that no care was taken to 

 use dry and pure gas in the former experiments. 



Some experiments were made to see whether the mobility 

 depended on the rate of alternation of the field. It might 



3G2 



