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VI. The Emission and Transmission of Rontqen Rays. 



By G. W. C. KAYE, B.A. (Cantab.), H.Se. (Lond.), A.R.C.Sc., Associate-Member 

 of the Institution of Electrical Engineers, Trinity College, Cambridge. 



Communicated l>y Prof. J. J. THOMSON, F.R.S. 

 Keceived June 17, Head June 25, 1908. 



OF recent years much interesting work has been done to connect the atomic weight 

 of an element with its power of emitting and transmitting various kinds of radiation. 

 One may mention McCLELLAND's* work on the secondary radiation given out by a 

 substance exposed to the /3 and y rays of radium, and Prof. J. J. TnoMSON'sf results, 

 which brought out the relation existing between atomic weight and the intensity 

 of the emitted secondary Rontgen radiation. In each case an increase in atomic 

 weight was accompanied by an increase in the amount of secondary radiation. 

 KLEEMAN J has obtained a similar result in the case of the secondary radiation 

 produced by the y rays from radium. 



BENOIST in 1901, working with the absorption by various elements of a definite 

 beam of Rontgen rays, obtained a smooth curve approximating to a rectangular 

 hyperbola by plotting atomic weight against a factor related to \/p (i.e., the absorption 

 of unit mass per unit area), where p is the density of the screen, and X is the coefficient 

 of absorption. X is defined by the exponential relation for a homogeneous beam 

 I = I e~ A< *, in which I is the intensity of the incident beam, and I that of the emergent 

 beam from a layer of thickness d. It follows from BENOIST'S curve that \fp increases 

 with the atomic weight, and more rapidly in the region of low atomic weights. 

 CROWTHER || measured the absorption by different elements of the j3 rays from 

 uranium, and obtained a periodic relation between atomic weight and \/p. 



It was thought that a careful study of the Rontgen radiation emitted by various 



* MCCLELLAND, 'Sci. Trans. Roy. Dublin Soc.,' 1905 and 1906. 

 t J. J. THOMSON, 'Proc. Camb. Phil. Soc.,' XIV., 1, p. 109, Nov., 190G. 

 J KLEEMAN, 'Phil. Mag.,' p. 618, Nov., 1907. 

 BENOIST, ' Journal de Physique ' (3), X., p. 653 (1901). 

 || CROWTHER, 'Phil. Mag.,' p. 379, Oct., 1906. 

 VOL. CCIX. A 446. R 2 19.11.08 



