Secondary y Radiation. 429 



same value when the radiation is tested by Zn or Al ; but 

 is considerably greater when tested by Pb. This is similar 

 to the results which are obtained when the original y 

 radiation coming from Ea, which apparently consists of a 

 mixture of hard and soft rays, is tested by small thicknesses 

 of absorbing screen. 



Table I. 



Pb Domes. 



Radiation from Pb. 



Thickness of Dome, mm 1 4 6 10 



100 80 60 43 26-5 



Radiation from Zn. 



Thickness of Dome, mm 2 4 6 10 



100 64 46 33 21 



Radiation from Al. 



Thickness of Dome, mm 2 4 6 10 



100 03 45 32 20 



Zx Domes. 



Radiation from Pb. 



Thickness of Dome, mm 5*4 11'7 253 



100 85 67-5 44 



Radiation from Zn. 



Thickness of Dome, mm 5*4 11*7 253 



100 84 63 34 



Radiation from Al. 



Thickness of Dome, mm 5*4 11-7 253 



100 81 59 33 



Al Domes. 

 Radiation from Pb. 



Thickness of Dome, mm 8 21 



100 88 75 



Radiation from Zn. 



Thickness of Dome, mm 21 



100 74 



Radiation from Al. 



Thickness of Dome, mm 21 



100 72 



It has already been shown that the radiation from the sides 

 of the cone is approximately of the same quality as that 

 Phil Mag. S. 6. Vol. 17. No. 99. March 1909, 2 G 





