﻿Secondary Rays excited by Alpha Rays from. Polonium. 813 



the reflexion and refraction when radiation is incident on a 

 crystal at a surface which is normal to a principal axis, the 

 planes of incidence and polarization containing the other 

 axes. 



With the same notation as before, in the transmitted wave 



fj = —^2 -j . ssin0icos{/e(#cos0+y sin — ct) — j3} } 



rji = s cos 6 X cos{/c(# cos 6 -\-y sin 6—ct) —/3\. 



The boundary disturbance in the crystal is found to be the 

 same as in an isotropic medium. The equations expressing 

 the boundary conditions are at once obtainable, and the solu- 

 tion follows. 



There is in general a change of phase at reflexion, but it 

 vanishes if V is very large, the solution then being identical 

 with that for an isotropic medium. 



From the phenomena of the reflexion the velocity of the 

 irrotational wave can be determined, or its relative largeness 

 established *. 



January, 1912. 



LXXVIII. On the Secondary Rays excited by the Alpha Rays 

 from Polonium. — I. By V. E. Pound, M.A.f 



1. Introduction. 



RECENT researches have shown that radioactive materials 

 from which a rays are sent off also emit a radiation of 

 negatively charged particles, which will not ionize a gas, 

 and which has been called $ rays. The other characteristics 

 of this radiation are that it is easily absorbed, it is easily 

 deflected by a magnetic field, and it is stopped by a small 

 positive charge placed upon the radioactive substance emitting 

 it. Still later researches by Logeman J and Aschkinass § 

 have shown that when u rays fall on a polished piece of 

 metal such as copper, this metal emits a secondary radiation 

 with characteristics similar to those of the h rays. Further, 



* It is hardly necessary to note that it is zero according to the electro- 

 magnetic theory. 



t Communicated by Professor J. 0. McLennan : read before the 

 Canadian Institute, Toronto, January 13, 1912. 



t Logeman, Proc. Roy. Soc. Series A, vol. lxxviii. Sept. 6, 1907. 



§ E. Aschkinass, Ann, der Fhys. no. 12 (1908). 



