

Dr. A. S. Eve on the Ionization of the 



present unknown, but it appears to be about equal to that o£ 

 the y rays in effect. Perhaps the distinction is an erroneous 

 one, but in any case we obtain an estimate of this sort — 



Rays. 



Ra. 



Th. 



Total. 



a, 



163 

 •035 

 •03.-) 



1-00 

 •025 

 •025 



263 

 •0G 

 0(J 



|3 







1-70 



105 



2-75 



(10) 



Thus 2 7 ions per cm. 3 per sec. is our value for the mean 

 total ionization, due to all the radioactive matter in the 

 atmosphere, near the earth's surface. It will be seen that the 

 a rays are mainly effective. 



We can, however, calculate the ionization due to the y rays 

 from radium C in a more direct way than above. If N is the 

 number of ions produced per cm. 3 per sec, A, the coefficient of 

 absorption of the y rays by air, Q the amount of radium C 

 per cm. 3 of the atmosphere, expressed in terms of the number 

 of grammes of radium with which it is in equilibrium, then 



- 



irr 2 drK% 



A '=27rQK/\. 



(11) 



(12) 



Here K = 3-1 xlO 9 , \ = -000044, Q-SxlO" 17 ; 

 whence N = 2tt x 3'1 x 10 9 X 8 x 10- 17 /4'4 x 10" 5 \ 

 — "035 ion per cm, 3 per sec. J 



This agrees with the former result (9). 



It is possible to use a formula exactly similar to (11) in 

 order to calculate the rate of production of ions near the 

 earth's surface, due to the radium C in the earth. In this 

 case K has the same value as before, but Q' = r4x 10~ ]2 x 2*7, 

 the mean value found for sedimentary rocks by Strutt, and 

 V = -034x2-7 (McClelland). 



Hence 



N' = 27rQ / K/A' 



= 2ttX 3-1 x 10 9 x 1 -4 x 10- 12 x2-7 

 •034x2-7 

 2ttx 31x1-4 



3-4 



xlO- 



0*80 ion per cm. 3 per sec. 



13) 



