loNIZATION BY POSITIVE IONS 49 



that /3='041. These values of a and j3 are in the ratio 

 of 57 : 1. Again, for argon N=13'6, and 



a=2T7 when X=105 and p=l, 

 /3=-025 when X=105 and #='25, 



giving the ratio a : /3=86 : 1. 

 For carbon dioxide N=20 and 



a=8'2 when X=215 o,ndp=l, 

 /3003 when X=215 and ^='25 



giving the ratio a : /3=1070 : 1. 



It thus appears that the greater the molecular weight 

 of the gas the greater the difference between positive and 

 negative ions as regards their efficiency in producing 

 new ions by collisions. 



In the case of pure helium the range of forces for 

 which observations of a and ft have been made is very 

 small, and it would not be possible to deduce numbers 

 from them similar to those found for other gases at the 

 point at which a=*16 N. The values of a and ft that 

 have been found for an impure specimen of the gas 

 containing about 98 per cent, of helium may be used. 

 They give the following results : 



a='5, X=25, p=l, 

 /30095, X=25, #=-25, 

 which gives a=52x/3. 



This result shows that the positive ions in helium are 

 less efficient than those in hydrogen, but it is remarkable 

 that the ratio of a to )3 should be nearly the same as 

 for air. 



When comparisons of the relative efficiency of positive 

 and negative ions in pure helium and in air are made, 

 using smaller forces which correspond to values of a 



I.G. B 



