﻿

in the Earth and the Atmosphere. 191 



because the secondary radiation due to transmitted rays is a 

 function of the thickness traversed*. 



If the penetrating radiation, discovered by McLennan, 

 and by Kutherford and Cooke, consists of 7 rays, it follows 

 that the weak ionizations resulting from it within closed 

 vessels made of different metals should have the sani3 

 characteristics as those determined in these experiments. 



It is now possible to calculate the value of K in formula (1) . 

 The value of N in the thin aluminium vessel was 297, and 

 this is probably not more than 10 to 20 per cent, in exce.-s 

 of the value in free air f 



Hence K = 297 x 303 2 /-014 



= 1-95 x 10°; 



or adding a small correction for the absorption by 3 metres 

 of air , 



K=2x 10°. 



But the 7 rays have been absorbed to a considerable extent 

 during their passage through 7 mms. of lead, and if we take 

 the coefficient of absorption of lead to be initially '01 J, the 

 intensity has been diminished by the factor e~' 6ix ' 7 , so that 

 the value of K is about 



2 x 10° x 1*56 

 or 



3'lxl0 n (2) 



This result has been calculated from the ionization within a 

 thin aluminium vessel, and it is, therefore, owing to secondary 

 radiation, probably about 10 to 20 per cent, in excess of 

 the value of K in the open air. The value of K within a 

 zinc or copper vessel is 3*6 x 10°. 



On the Total JS'umber of Ions generated per Second by the 

 7 Rays from a Gram of Pure Radium Bromide. 



It is now possible to determine the total number of ions 

 which would be generated every second by the 7 rays from 

 Q grams of pure radium bromide, surrounded entirely to a 

 great distance by air, so that the rays are all absorbed by it. 



If \ is the coefficient of absorption of the 7 rays in air, 

 then at a distance r the number of ions produced per second 



per c.c. by the 7 rays from Q grams is ^r^- Xr , and in a 



* Eve, Phil. Mag. Dec. 1904. 



t Eve, ibid. 



X McClelland, Phil. Mag. July 1901. 



