332 
PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
gives the source of the homogeneous rays used to ionize the gases ; column II. the 
approximate wave-length of the radiation; column III. the mass coefficient of 
absorption of the radiation in aluminium; column IV. the ratio of ionization 
coefficients in ethyl bromide and in air. Thus when two similar beams of radiation 
traverse two equally thin layers of ethyl bromide and air at the same pressure and 
temperature, and in each case the gas absorbs its own corpuscular radiation 
completely, and all fluorescent radiations of no greater penetrating power than 
this corpuscular radiation, the ionization in ethyl bromide varies from 50 to about 
342 times that in air as the wave-length of the radiation diminishes, or from 
50 to 475 times that in air by K, L, M... corpuscles (electrons) alone, as we shall 
see later. Of course the ratio of the absorption in ethyl bromide to that in air is 
also high, and it varies with the wave-length of the radiation used. It should be 
pointed out, however, that the K characteristic radiation from bromine when excited 
was allowed to escape without adding its effect to the total ionization measured in 
ethyl bromide. 
Thus when Cu, As and Se “ K ” radiations were used as ionizing agents, the 
ionization in ethyl bromide (produced by L, M, N electrons) was about 50 times 
that in air. But when Sr, Mo, Ag, &c., radiations were used, the “ K ” corpuscular 
radiation was emitted by the bromine in ethyl bromide and produced an increase in 
the relative ionization. Subtracting 50 from the values in column IV. we get the 
effect of the additional (K) electrons, i.e ., 
ionization in C 2 H 5 Br due to K electrons alone 
ionization in air by K, L ... electrons 
as given in column V. Column VI. gives the relative absorptions of the ionizing 
radiations in ethyl bromide and air at the same pressure and temperature. Here 
again there is a large increase when the particular radiation is of sufficiently high 
frequency to excite the K radiation in bromine. Subtracting the ratio obtained 
when no K fluorescent radiation was excited from that obtained when it was 
excited, we get the values in column VII. which consequently represent the 
K absorption in C 2 IT 5 Br 
absorption in air (K, L, M, ...)' 
Dividing values in column IV. by the corresponding values in column VI. we get 
ionization in Cd=L 5 Br ionization in air (K, L, ...) 
absorption in C 2 H 5 Br ’ absorption in air (K, L, ...)’ 
