(73) 
ON THE VELOCITIES OF TWO DISTINCT GROUPS OF 
SECONDARY CORPUSCULAR RAYS PRODUCED BY A 
HOMOGENEOUS RONTGEN RADIATION, AND THEIR 
ABSORPTION COEFFICIENTS IN VARIOUS GASES. 
By Lewis Simons, B.Sc.(Lo]srD.). 
(With six Text -figures.) 
(Figs. 2, 3 and 5 are in the form of folding plates and are inserted 
together at the end of the paper.) 
Part I. 
The emission of a so-called homogeneous corpuscular radiation from a 
metal plate during the incidence of Rontgen rays upon it has been studied 
in detail by Sadler* and Beatty.f By using homogeneous beams of Lenard 
rays Whiddington showed that the law expressing their velocity as a function 
of the depth of matter passed through could be written | — 
[i) . . . I'o - Vj- — ax, 
the constant a depending upon the nature of the absorbing material, but no 
relationship could be traced between the value of a and the density or 
atomic weight of the absorbers. In a later paper § he showed, from the 
experimental results of Sadler and Beatty, that the maximum velocity of the 
corpuscular rays ejected by a characteristic Rontgen radiation was proportional 
to the atomic weight of the radiator supplying the Rontgen rays, and that 
this maximum velocity was independent of the nature of the substance from 
which they were ejected. Barkla and Shearer || have extended this result 
so as to include either the " K " or "L" cathode rays, their conclusion being 
that the maximum velocity of ejection of the particles, wherever be their 
source in the atom, is the same for the incidence of a given wave-length of 
Rontgen radiation. 
The object of the work undertaken in this paper was twofold : 
(1) To investigate the absorption coefficients of the secondary corpuscular 
rays in various gases. 
* 'Phil. Mag./ [6] xix, p. 837 (1910). 
t Ibid., [()] XX, p. 320 (1910). 
X ' Proc. Roy. Soc.,' a, Ixxxvi, p. 370 (1912). 
§ Ibid., p. 376. 
II 'Phil. Mag.; [6] xxx, p. 753 (1915). 
