102 Mr Growther, On the secondary Rontgen radiation 



been directly verified, and in the light of Prof. Bragg's interesting 

 suggestion, it was thought desirable to make some direct experi- 

 ments on the point, and to compare the relative amounts of 

 ionization produced by the secondary rays from ethyl bromide 

 and from air, in some gas not so unfavourable as air, to the 

 harder radiations. 



Methyl iodide, and ethyl bromide suggested themselves as the 

 most likely for the experiments. The ionization produced by the 

 primary rays in both is very large, and their coefficients of absorp- 

 tion for the primary rays are also large. The values obtained for 

 ethyl bromide, however, vary less rapidly with the nature of the 

 rays than those for methyl iodide, so that comparable results 

 are more easily obtainable with it than with the latter. On the 

 whole, therefore, ethyl bromide was preferred; and the experiment 

 consisted in comparing the amounts of ionization produced in 

 ethyl bromide by the secondary rays from ethyl bromide, and 

 from air. 



To Cells 



^>w 



/' 



To Electrosfiope 





B 



To EarlTi 



; / 



"1 



p 





-1' 



-r^ y= V- 



/ A 



The apparatus employed was a modification of that used in 

 my previous researches* on the subject, and it will not be neces- 

 sary to describe it in any great detail. The radiating gas was 

 contained in a rectangular brass box A ; the primary rays entering 

 through an aluminium window G ; while the secondary rays passed 



* Crowther, Phil. Mag. [6], Vol. xiv. p. 653, 1907. 



