Particles by Homogeneous Rontgen Radiations. 329 



Discussion of Results. 



Shortly after the preliminary account of this paper had 

 been read *, a research was published by C. A. Sadler f in 

 which he studied the emission of cathode particles from various 

 metals under the influence of homogeneous radiations. His 

 numbers, which agree remarkably well, considering the 

 difficulties of the investigation, show that the penetrating 

 power of the cathode particle is independent of the metal in 

 which it originates, and only depends upon the nature of the 

 exciting radiation. The numbers which he obtains for the 

 coefficients of absorption by air of these cathode particles,, 

 while trending in the same way as those given in this paper, 

 show numerical differences, particularly in the case of the Sn 

 radiation. 



Since the particles in Sadler's experiments emerged from 

 the incidence side of the metal, while those treated of in this 

 paper came from the emergence side, it seemed possible that 

 the cathode particles emerging from opposite sides of the 

 plate might show a want of symmetry in penetrating power. 

 Accordingly the silver leaf was removed from RK (fig. 2) 

 and affixed to the lower side of E, so that cathode particles 

 could only emerge from its incidence side. The coefficients 

 of absorption by air were then determined for the particles 

 excited by the Sn, As, and Fe radiations in exactly the same 

 way as before, and the important discovery was made that 

 the coefficients of absorption of these particles are the same 

 whether they come from the incidence or emergence side of 

 the silver leaf. 





Table VI. 





Radiator. 



\ on emergence side. 



X on incidence side. 



Sn 



3-97 

 2743 



87-2 



3 91 



281 

 85-0 



As 



Fe 





This point being settled, various alterations were made in 

 the experimental arrangements in order to test the effect of 

 altering the geometrical conditions. It was thought that the 

 obliquity of incidence of the radiations (see fig. 1) might 

 account for the differences in the values obtained, so the 



* Beatty, Proc. Camb. Phil. Soc. vol. xv. pt. v. pp. 416-422, February 

 21,1910. 



t Sadler, Phil. Mag. March 1910, pp. 337-356. 



Phil. Mag. Ser. 6. Vol. 20. No. 116. Aug. 1910. Z 



