PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
333 
which is 
ionization in CoH 5 Br 
ionization in air (K, L, ...) 
for equal absorptions of the ionizing radiations (column VIII.). 
Similarly dividing the values in column V. by the corresponding values in 
column VII. we get 
ionization in CJELBr due to K electrons 
for equal absorptions 
ionization in air (K, L, ...) 
of the ionizing radiations (see column IX.). 
Thus column VIII. gives ionization in ethyl bromide due to L, M, N, &c., electrons, 
relative to ionization in air due to K, L, M, N, &c., electrons, produced by equal 
absorptions in the two gases. Column IX. gives ionization in ethyl bromide due to 
K electrons alone, relative to ionization in air due to K, L, M, N, &c., electrons, for 
equal absorptions of the ionizing radiation in the two gases. As ionization produced 
in a given gas by a given homogeneous X-radiation is proportional to the number 
of electrons in the corpuscular radiation producing that ionization, we see from 
columns VIII. and IX. that when the exciting primary radiation is of just shorter 
wave-length than the bromine K radiation, the K absorption is accompanied by 
the emission of a much smaller number of electrons than is the L, M, N absorption. 
For instead of 205, 194, 193, L, M, and N electrons, there are emitted 87, 104, 125, 
142, 144, K electrons for primary radiations of higher frequency; or for equal 
absorptions of energy there are only about half as many K electrons emitted as 
L, M, ... electrons, when the primary radiation is of just shorter wave-length than the 
K characteristic radiation. As primary radiations of shorter and shorter wave-length 
are used, the number of K electrons emitted more closely approaches the number 
of L, M, ... electrons emitted for an equal absorption of energy of primary radiation. 
At first sight it appears from column VIII. as though twice as many electrons are 
emitted from C 2 H 6 Br as from air when equal absorptions of Cu, As and Se radiations 
take place. This, however, is due to the fact that more ions are produced by a high 
speed electron moving through C 2 H 5 Br than through air. The former is more easily 
ionized. The factor by which the numbers 2‘05, 1 '94, 1'93, &c., in columns VIII. 
and IX. must be divided to give the relative numbers of electrons emitted by CfH 5 Br 
, . . • , t ..hr* * m number of L,M,N, ...electrons emitted by Br 
and air is approximately 1 75. Ihus -r- . ’ , ’ -,— - r———— 
number o± K, L, M,... electrons emitted by air 
and 
for equal absorptions of energy are 
number of K electrons emitted by Br 
number of K, L, M,... electrons emitted by air 
given in Table IV., columns II. and III., for primary radiations of wave-length 
indicated in column I. 
* The value given by Barkla and Philpot (‘ Phil. Mag.,’ June, 1913) as a first approximation was 1 -6. 
This, however, needed a small correction, the magnitude of which was unknown at the time, but has since 
been found from experiments by Carse to raise the value to about 1 4 75. The correction was necessary 
on account of the appreciable reflexion or return through the face of incidence of corpuscles on entering 
the substance ethyl bromide. 
3 A 2 
