378 Prof. C. G. Barkla on Typical 



"Now Mr. Sadler has determined the total ionization pro- 

 duced in air by the corpuscular radiation from the incident 

 face of plates of various substances compared with the 

 ionization produced by the exciting X-radiation in a layer 

 of air 1 centimetre thick. Call this Rj. 



The total ionization of corpuscular radiation 



= Wdx, 



Jo 

 [z a r is the ionization coefficient of corpuscular radiation in air~\ 



i 



1 ? 



n 



— thei 



n 



• /J-0 l a JirC 1() 



X a X a X 



Aa A# 



I ' 1 



~ Jlk i a ' xV" 



{1 i ' l a 1 



TT-^-T^Xa ?- Rl. 

 /l V la J 



Now ^ in the case considered is the ratio of ionization in 



air to ionization in air and ethyl bromide, when the corpuscular 

 radiation is not excited. 



This == =tv approximately. 



^7 is the ratio of ionization in air and ethyl bromide to 



la 



that in air, produced by the corpuscular radiation alone. 

 This is very approximately equal to 



density of air and C 2 H 5 Br __,„ 

 density of air 



\a is the absorption coefficient in air of the corpuscular 

 radiation from Br (or anything else) excited by the particular 

 primary radiation. 



Take the case of ionization by the radiation from Ag. 

 X a ' = 8'8 approximately. 



(See Sadler's paper on " Homogeneous Corpuscular 

 Radiation," Phil. Mag. March 1910.) 



Rj is the quantity defined ; and by interpolation can be 

 shown to be about '8 for Br. For the mixture of air and 

 ethyl bromide used in these experiments Ri would be less 



than this, as .-7 is less, the active substance Br being diluted. 



