Radiation from Substances of Low Atomic Weight. 14.*) 



and the total ionization in the tertiary electroscope may be 

 written 



A[i.(i-r^)+i 2 (i-r^)] 



(A and k being constants of the electroscope ; A including 

 a correction for obliquity of the rays.) 



= AfaTi + ^Tg] sa J- 



Let 1/ and I 2 ' be the intensities after the first absorption 

 by a plate of aluminium. The total ionization in the electro- 

 scope will then be 



Ar«v+Myi. 



If \i be the absorption coefficient of the unknown homo- 

 geneous radiation, and X 9 that of the homogeneous secondary 

 radiation, in aluminium, and x x the thickness of the first 

 aluminium absorber, 



T-r / X^r, x I 



1 = .1 j e l ' = m l [ l say 



Tt ' X .r, t ' 



2 — J 2 e - " = n x \ 2 ,, 



If \ = the 1st apparent absorption coefficient of the mixed 

 beam, 



\x x _ alx + bl 2 

 6 "aV + 6I 2 '- 



Similarly, if i± and i 2 be the intensities, after a further 

 absorption by a second plate of aluminium of thickness x. 2 , 

 and X' the second apparent absorption coefficient, 



\V 2 _ all 4-frlY 



aii + bi% 

 and 



II ' X T • 



i = % x e l - = m 2 i\ 



\ i • X .r., 



J 2 = & 2 <? " = "V'2- 



Substituting", we have 



and 



" " ai/+6]y (ij 



a\ x b\ 2 

 m 9 n* 



from (1) 

 Phil. Mag. S. 6. Yol. 24. No. 139. July 1912. L 



Ii' = 6 Oir^i 

 V a' ( e X ^-nii) 



