1908] on the Carriers of Positive Electriciti/. 201 



ionized by a particles than one ionized in any other way, shows that 

 results of ionization are different in the two cases : this result is, 

 however, exactly what we should expect if there were no such 

 difference. For when a gas is ionized by a rays, each a particle 

 produces an enormous number of ions, but there are comparatively 

 few particles, and these are Avidely separated. Thus in a gas ionized 

 by a rays we have intense ionization in some locaHties and very weak 

 i onization in others, while other methods give much more uniform 

 ionization. Now the electric foice required to saturate a gas depends 

 upon the maximum density of ionization as well as upon the average ; 

 thus it will require a more intense field to saturate a gas ionized by 

 a particles than a gas where the total ionization is the same but the 

 ionization is uniformly distributed through the gas. The researches 

 of Moulin * on the ionization by a rays, show that the differences 

 "between this kind of ionization and others can be explained as 

 arising from the want of uniformity in the distribution of the a 

 ionization. 



I have much pleasure in thanking Mr. E. Everett and Mr. 

 G. W. C. Kaye for the assistance they have given me in this investi- 

 gation. 



[J. J. T.] 



* Le Badium, t. v. March 1908. 



