the Fluorescent Rontgen Radiations, 401 



accurately tested. It appears probable that the radiation 

 from these elements contains a greater proportion of scattered 

 radiation. There is also the possibility of the superposition 

 of a small quantity of a second more penetrating fluorescent 



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radiation. The full analysis of these radiations when excited 

 by homogeneous primary radiations would lead to more 

 accurate conclusions. Experiments on the resultant secon- 

 dary radiation show, however, that these radiations are very 

 homogeneous in comparison with any ordinary primary 

 beam. The fluorescent radiations are thus at any rate 

 approximately homogeneous, and in the absence of more 

 exact evidence will be considered homogeneous, like those 

 radiations upon which more accurate experiments have 

 hitherto been possible. 



Indirect evidence that the fluorescent radiations are ap- 

 proximately homogeneous has also been obtained by Barkla 

 and Collier in studying the relation between the absorption 

 of homogeneous X-rays in platinum and gold and the absorp- 

 tion of these rays in aluminium. The curves showing the 

 relation exhibit similar characteristics to those obtained from 



