Currents to the Study of Ionization by Collision. 477 



drawn the values of a/P corresponding to the values of X/P 

 given in Townsend's paper have been read off, and are 

 given, together with Townsend's results, in the following- 

 table : — 



X 



p* 



a 



F 



(From fig. 5.) 



P" 



(J. S. Townsend, 

 Ph. Mag, 1903, vol. vi.) 



350 



5-28 



5-25 



395 



5-86 



5-8 



437 



6-32 



63 



480 



6-77 



6-8 



530 



7-21 



7-27 



662 



8-18 



8-42 



787 



8-82 



8-9 



It will be seen that the values of a/P corresponding to 

 these higher values of X/P are also in good agreement 

 with the values obtained by Townsend. The ionization in 

 these experiments takes place at temperatures up to 100° C. 

 higher than the temperature in Townsend's experiments, and 

 this general agreement of the results is direct evidence that, 

 in the case of negative ions, the power of ionizing by col- 

 lisions in a gas of given density is independent of the 

 temperature within these limits. 



The author wishes to acknowledge his indebtedness to the 

 Government Grant Committee of the Royal Society for 

 the means of purchasing some of the apparatus used in these 

 experiments. 



Royal Holloway College, 

 Enelefield Green. 



Phil. Mag. S. 6. Vol. 31. No. 204. Dec. 1917. 



2M 



