OC/P 



476 Prof. F. Horton on the Application of Thermionic 



The temperature of the gas at these pressures was found 

 to be 86° C, and the pressures were corrected to the values 

 they would have if the gas were cooled at constant density 

 to 17° 0. The values of X/P, «/P, and /3/P were thus 

 found to be : — 



X | a 

 P* P' 





 P' 



619 

 1253 



7-85 

 9-94 



•0077 

 •193 



The values of /3/P are much smaller than those obtained 

 by Townsend. For X/P = 619, Townsend's value of /3/P 

 is *104. The greatest value of X/P in Townsend's experi- 

 ments was 787, at which his value of /3/P is *18, and, from 

 the general shape of the curve *, it would appear to be 

 more than '3 when X/P = 1253. It therefore looks as 

 though the positive ions obtained by collisions in these 

 experiments were less active ionizers than those produced 

 in the ultra-violet light experiments ; but it seems desirable 

 to verify these small values of /3/P by further experiments 

 before attempting to explain them. In order to compare 

 the values of «/P obtained in this research with those 



Efc. 5. 



, y\ i N T ! i \ i i 



fczzn±rrztz_LU+-U:== 



100 200 300 400 500 

 X/ p 



900 1-000 IIOO 1200 1300 



obtained by Townsend, for values of X/P greater than 300 

 (the higher limit of the curve in fig. 4), the values of X/P 

 and a/P have been plotted in fig. 5. From the curve 



* J. S. Townsend, Phil. Mag. (6) vi. p. 598 (1903). 



