ADAMS. — TRANSMISSION OF RONTGEN RAYS. G97 



(3) An efl'ect o^ absorption sufTered by the several components of the 

 beam in passing through th^ substance of the screen. 



Experimental results rule out, more or less certainly, the first two 

 effects. Granting these results, a theory of relatively selective ab- 

 sorption is necessary to explain the reduction of penetrating power for 

 one metal by transmission through another. By somewhat indirect 

 experimental evidence, this absorption is shown to be governed by 

 coefficients which are probably constant with varying intensity of 

 the rays. 



VI. Conclusions. 



The following conclusions are reached in this paper : 



(1) The approximate measurement of the energy of Rihitgen rays is 

 of the same order of magnitude as the earlier measurements of that 

 energy, and to that extent confirms them. 



(2) In the transmission of Runtgen rays through metallic sheets, the 

 effect of the surfaces of the metal is small. 



(H) In the transmission of Rontgen rays through metallic sheets, the 

 probability that one sort of ray is transformed into another sort of ray, 

 to an appreciable extent, is small. 



(4) The absorption of any particular sort of ray by a metallic sheet is 

 measured by a coefficient which is probably independent of the intensity 

 of that ray. 



(5) In one special case, at least, the general effect on absorption by 

 one metal of passing the rays through another metal is not, so far as 

 we can judge, a decrease of absorption, but an increase ; and this fact 

 tends to support the theory that the radiation irom an ordinary tube 

 is heterogeneous in character, and that the absorption in metallic 

 sheets is more or less selective. 



It is hoped to continue this research in the direction suggested by 

 the conclusions of this paper : to test the hypothesis of relatively se- 

 lective absorption by direct experiment ; ^^ to obtain, if possible, beams 

 of Rontgen rays which will yield transmission curves of a simpler form 

 than those heretofore found ; to study the properties of those beams ; 

 and to study the indications of the instrument used in this research in 

 comparison with those of other instruments heretofore used, especially 

 the ionization -electroscope and the photographic plate. 



21 For a preliminary note on this experiment, see Amer. Jour. Sci., 173, 91 

 (1907). 



