776 Mr. H. Pealing on Distribution and Quality of 



Table IV. 



Thickness of aluminium 

 absorbing secondary rays. 



Values of 



140 

 190 



Absorption of secondary 

 rays by thickness of alumi- 

 nium given in column 1. 



none 

 015 mm. 

 095 mm. 

 1*6 mm. 

 3'2 mm. 



1-69 

 1-72 

 1-74 

 1-88 

 1-97 



none 

 14*9 per cent. 

 55 per cent. 

 67 per cent. 

 84 per cent. 



When the hard portions of a very hard beam were used the 

 ratio fell to 1*75. 



Somewhat similar results were obtained when the hard 

 portions of a hard primary beam fell on the radiator. 



They are shown in Table V. 



Table V. 





Thickness of aluminium 

 absorbing the primary 

 beam. 



Values of 

 Lin. 

 190 



Thickness 'of aluminium 

 absorbing the secondary 

 beam.. 



(a) 



none 



1-67 



none 





0*15 mm. 



1-69 



none 





0-95 mm. 



1-72 



none 





1*6 mm. 



1-88 



none 





3-2 mm. 



1-80 



none 



Q>) 



none 



2-03 



3-2 mm. 



none 



1-67 



0*15 mm. 





3-2 mm. 



T54 



0*15 mm. 



Table V. (V) gives the results for a moderately hard bulb, 

 while (6) gives the results for a very hard bulb. In the 

 latter experiments the secondary beam was absorbed by thin 

 aluminium to get rid of the iron radiation present. 



It is seen that the ratio rises with the hardness of the 

 beam, but when very hard rays are used the ratio drops 

 again. 



All these results can be explained by the existence of an 

 " extra " carbon radiation, Crowther * has argued that it 

 is an indirect effect of the corpuscular carbon radiation. It 

 is easy to see that it will not differ very much from the 

 primary in penetrating power. Those corpuscles which are 

 * Crowther, Proc. Phil. Soc. Camb. pp. 534-539 (1912). 



