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SCIENCE PROGRESS 



the rays emerging through any one slit had the same quality, 

 and that those produced by the swiftest cathode particles had 

 the greatest penetrating power. 



Rontgen rays heterogeneous. — About 1897 it was noticed by a 

 number of observers that the Rontgen rays from a coil-driven 

 tube do not satisfy a test for homogeneity, in that their quality, 

 judged by their penetrating power for various substances, is 



E 



Fig. 2. 



changed by transmission through metallic sheets. That a range 

 of hardnesses of X rays should accompany heterogeneous 

 cathode rays would of course be expected. The rate of cutting 

 down of the Rontgen rays is more pronounced when the 

 interposed screen is thin than when it is thick (the soft rays 

 being sifted out first), or, as it will be convenient to regard it, 

 the coefficient of absorption (X) diminishes as the thickness 

 of screen increases and harder rays are dealt with. \ measures 

 the fraction of the intensity absorbed by unit thickness of screen, 



