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PROF. C. G. BARKLA ON X-RAYS AND THE THEORY OF RADIATION. 
the atom, and is radiated when that configuration returns to its original state. It 
thus of necessity appears in certain processes of absorption and radiation.* 
The results obtained by certain experimenters on the ordinary production of 
primary X-radiation suggest, too, that mere collision of electrons with an anti-cathode 
is not sufficiently sudden, or of sufficiently violent a nature, to result in the pro¬ 
duction of the X-rays as ordinarily detected. The probability is rather that the 
function of the cathode particle is to displace electrons from their normal positions 
in atoms of the anti-cathode, and thus to produce in these atoms vibrations—some 
characteristic, others not—which result in the emission of the primary radiation. 
* There is no need to indicate the problems of absorption and radiation still awaiting solution. 
Though there is no evidence as to the nature of the mechanism involved in these processes beyond what 
is indicated by a change from certain initial to certain final conditions these investigations seem to 
establish many important facts, and to show' the narrow limits within which the quantum theory is in any 
sense applicable. 
iry-tOiMI i. 
1 SEP.1917 
