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PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
But again, what we have observed is in this case 
K corpuscular radiation+ L characteristic radiation accompanying K electrons (energy) 
K primary absorption (energy) 
which should accordingly be compared with --- L - . . , as in columns IY. and V. 
n + n K + n h +... 
In column YI. the total energy of secondary radiations associated with the emission 
of K electrons is expressed as a fraction of the K absorption, as in Table YI., 
column YI. 
The agreement between theory and experiment, as shown in Table YII., is, on the 
whole, very close. 
The experimentally observed energy relations, however, are not sufficiently accurate 
to enable us to determine with certainty the exact process by which the original 
configuration of the atom is regained. 
In fundamentals, however, the theory can scarcely be questioned. It explains so 
many facts and is so simple in itself that there seems no alternative but to accept it 
in outline at least. 
[The principal facts which may be regarded as giving support to the theory may be summarised as 
follows:— 
(1) When fx is just less than /x K for any one of the heavier elements, the fraction of the primary energy 
aibsorbed (K absorption) transformed into K characteristic radiation ( jt- ) is slightly less than 0 * 5 
(2) There is evidently a limiting value of about 0 - 5 for the fraction. 
(3) As ix diminishes this fraction invariably diminishes. 
(4) In the one substance carefully investigated—a substance giving the maximum value just below 0 • 5— 
the rate of diminution of this fraction with diminution in /x is almost perfectly that given by theory. 
(5) When y is just less than fx K for the one substance thoroughly investigated, the fraction of primary 
/ C, 
energy absorbed (K absorption) transformed into K corpuscular radiation l ) is also slightly less than 0 • 5. 
This is approximately true for many substances, though a value appreciably but not considerably less than 
0 • 5 has been obtained. 
(6) The value exceeding 0 1 5 has never been observed. 
(7) As p diminishes, the fraction invariably increases. 
(8) In the one substance investigated, the rate of increase of the fraction is approximately the theoretical 
rate when fi is not near to /x K . (But when jx is near to /* K there is probably a real deficiency of corpuscular 
radiation.) 
(9) There is no evidence against the theory in its essentials. 
(10) The theory is a very simple one.] 
Experiments were commenced with Mr. Shearer with the object of determining 
whether the emission of K electrons was accompanied by a weak L radiation 
additional to that associated with L electrons, but the investigation was interfered 
with by war work, and did not get beyond the preliminary stage. The intensity 
was, however, seen to he very small. Theory as indicated above would lead us to 
