from Ordinary Materials. 

 Table III. 



54a 



Material. 



Absorption Coefficient. 



1 



| 



Lead 



Tin 



1 2 3 



! 



4 j 



Mean. 



6*91 128 1-3 

 0-45 ! 000 0-71 

 0-27 0-52 0-47 

 061 j ... 

 036 



0-56 j ... 



1 



1-18 

 0-8 



0-52 



1-00 



0-7 



... 



i 



117 

 0-65 



0-44 

 0-8 

 0-58 

 0-56 



Carbon 



Aluminium 



Zinc ... 



Platinum 





Table IV. 



Material. 



Increase 



of Leak. 



Lead 



Tinfoil 



Aluminium 



Zinc 



Carbon 



Observed. 



Calculated. 



0-023 



0025 



0-0075 



0-0055 



0020 



lO 1ft "* t> 



Tfi O CO I- <M 

 <M CO © O CM 



© © © © © 



6 6 6 6 6 



But I think the experiments have proved sufficiently that the 

 coefficient of absorption is not the same for the rays from 

 different materials — that each material emits rays of a quality 

 peculiar to itself. 



The importance of this conclusion, if accepted, can hardly 

 be overestimated. If the rays from different materials are 

 of different quality, it is impossible that they should be given 

 out by traces of a radioactive impurity common to all. Again, 

 the presence of a radioactive impurity — a suggestion that 

 has received considerable support — seems hardly able to 

 explain the remarkable constancy of the intensity of the 

 radiations emitted by samples ol metals derived from different 

 sources. 



§ 13. Experiments in which the plates of metal outside 

 the window were backed with .-labs of' iron 2'5 cms. thick 

 confirmed the conclusion previously reached that part of the 

 radiation from zinc, tin, and carbon i- secondary, excited by 

 a penetrating radiation from outside. 



