0. D. Cooksey — Secondary Cathode Rays. 



KI e e ax 



and the total number getting out of the whole plate is 



-pt pt 03-2,)* 



53 



= KI - X 



dx 





r (3-2,^ _ l ~] _ 



The X-rays after being absorbed in the plate on the front of 

 A are absorbed by the air in A and by the plate on the back 

 of A. Therefore the intensity of these rays after reaching a 

 .depth x of the second plate will be 



■i,t 



£ 



where t' is the length of the ionization chamber. Therefore 

 the number of incidence cathode rays getting into the ioniza- 

 tion chamber from the second plate of thickness t will be 

 equal to 



KI e — (^i* + V) 



jV.rtf+AOT] 



The ratio of the number of emergence cathode rays entering 

 A to the number of incidence cathode ravs is therefore 





e/i = R 7T 



€ — 1 



(i9+a,)« : 



€ 1 



Since A, is small compared to /3, the most important part of 

 this equation is Re * 1 ' Designating the other factors by S we 

 may write 



R = 



e/i 



If we assume that the absorption coefficient of the cathode 

 rays is proportional to the density of the absorbing material 

 we can calculate the values of /3 from the values given by 

 Sadler* for their coefficient in air. 



Sadlerf has measured the coefficients of absorption in air of 

 the fluorescent radiations characteristic of copper and arsenic, 



*Phil. Mag., vol, xxii, p. 447 1911. f Loc. cit. 



