722 Prcf:ssor C. G. Barkia [May 26, 



From measurements of the energy absorbed and the energy 

 re-emitted as corpuscular and as fluorescent characteristic X-radia- 

 tions, certain very important conclusions may be drawn. The 

 significance of the results is most easily understood if we express 

 them approximately. [Energy has been measured by the ionization 

 method.] 



Let the wave-length of the primary radiation be A and that of 

 the K fluorescent characteristic radiation of the substance bromine 

 be Ak. Then when A is greater than Ak, for a given absorption of 

 the primary radiation the same number of electrons is emitted by 

 bromine (L, M, N, etc., electrons) as by air (K, L, M, N, etc., 

 electrons). When A is just less than Ak the additional K absorption 

 in. bromine is accompanied by the emission of only half as many 

 electrons, that is, only half the K energy absorbed is re-emitted as 

 energy of K corpuscular radiation. But as A becomes smaller, an 

 increasing fraction of the energy absorbed (K absorption) goes into 

 the K corpuscular radiation. And the rate of change indicates that 

 with a primary radiation of very small wave-length practically the 

 whole of the K absorption would be accounted for by the K corpus- 

 cular radiation alone. There is in addition very strong indirect 

 evidence that when A is very small nearly all the energy absorbed is 

 re-emitted as corpuscular radiation, for whatever the absorbing 

 substance under these conditions the energy of this corpuscular 

 radiation is approximately a constant. 



Also when the wave-length A of the primary radiation is just less 

 than that Ak of the fluorescent X-radiation, of the energy specially 

 absorbed in association with the emission of the fluorescent radiation 

 (K absorption) nearly 0-5 is re-emitted as fluorescent X-radiation. 

 As A becomes less the fraction diminishes almost proportionately until 

 for primary radiation of very small wave-length the energy of the 

 fluorescent radiation becomes a very small fraction of the energy of 

 the primary radiation specially absorbed. It is evident at once that 

 the energy of K fluorescent X-radiation from bromine is approxi- 

 mately complementary to that of the K corpuscular radiation. From 

 the study of these relations we find : — 



The energy of primary radiation absorbed to expel one K elec- 

 tron is greater that that required to expel one L electron, by a 

 quantum of the K radiation. We then naturally consider the K 

 electron to be nearer the centre of the atom, and conclude that in 

 general the electrons associated with the higher frequency X-radia- 

 tions are nearer to the centre than those associated with lower 

 frequency radiations. Thus J, K, L and M electrons are arranged 

 in this order from the centre outwards. 



As both K and L electrons leave the atom with the same velocity 

 —this has been recently demonstrated — we may express the fact in 

 this way : A quantum of K radiation is the energy required to move 

 an electron from the position and state of a K electron to the position 



