240 



Prof. J. A. McClelland on 



rays examined by placing different thicknesses of tinfoil first 

 at B and then at A. The apparatus was then arranged as in 

 fig. 1, and the absorption of the secondary rays measured by 

 placing sheets of tinfoil at the end of the tube T. 

 The results are as follows : — 



Sheets of foil. 

 Each -013 mm. thick. 



Primary 



•ays. 



Secondai-y rays. 



Tinfoil at 



iouization- 



tube T. 



Tinfoil 26 cms. 



from ionization- 



tube T. 



Tinfoil at 



ionization- 



tube T. 



No foil 



100 

 60 

 47 

 39 

 32 

 27 

 22 



100 

 96 

 90 



77 

 66 

 49 

 35 



100 



80 

 64 

 44 

 26 

 9 



] 



2 



4 



8 



16 .. 



32 





V, 







































i 1 



V 



V 





































! 







\ 



N 









































\ 



\ 



































1 









\ 



v 



s 









































\ 



\ 



\ 



y 































: ! 











V 





y 



v+ 





























; 











H 



v 





X 



X 

































\ 







\ 







































\ 



\ 







\ 







































\ 







\ 



\ 



































\ 



\ 







\ 



N 





































^ 



\ 



































' D 











































; x /7. 



rfff 



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*j\. Pft/WPY 



















































































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. ^~*B.S£(W0W 



i 



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! i 

 1 i 



Curve A, fig. 5, refers to the primary rays when the 

 absorbing tinfoil is placed 26 cms. from the ionization-tube : 



