462 Prof. Bumstead and Mr. McGougan on Emission of 



structure of. the ring of electrons, and possibly with its period 

 of free vibration. The general evidence indicates strongly 

 that the transformation of energy from the 7 ray form to the 

 ft ray form or vice versa takes place in definite units which 

 are characteristic for a given ring of electrons but vary 

 from one to the other. The transformation of energy of the 

 ft ray form into the 7 ray form appears to take place far more 

 efficiently during the disintegration of an atom than when 

 ft rays fall on the atoms of ordinary matter. This is not 

 unexpected, for the conditions in the former case are emi- 

 nently favourable to the conversion, since the ft particle passes 

 directly through the electronic distribution of the atom. It 

 is at the same time to be expected that some of the energy 

 of the 7 rays which are formed within the atom should also 

 be converted, in part at least, into ft rays again, and should 

 thus give rise to one or more groups of homogeneous rays. 

 It is possible that two groups of slow velocity ft rays which 

 appear during the transformation of radium itself may arise 

 in consequence of such a transformation of the 7 rays set up 

 by the escape of the a particles from the atom. J. Chadwick, 

 working in the laboratory of the writer, has recently obtained 

 evidence that a. rays are able to excite 7 rays in falling on 

 ordinary matter. 



If this be the case, it is to be expected that all a ray pro- 

 ducts should emit some ft rays and 7 rays, though probably 

 of very weak intensity in both cases. The excitation of 

 7 rays by a rays is not improbable if the energy of the charged 

 particle rather than its velocity is the determining factor ; 

 for although the velocity of the a particle is small compared 

 with that of the ordinary ft particle, its energy of motion is 

 much greater. 



University of Manchester. 

 Aug." 16, 1912. 



XLIV. On the Emission of Electrons by Metals under the 

 Influence of Alpha Rays. By H. A. Bumstead and 



A. G. McGougan, Yak University*. 



Introduction. 



IN a previous paper under the same title by one of the 

 present authors t> an account was given of some expe- 

 riments upon the so-called S-rays which are emitted by 



* Cominunicaied by the Authors. 



t Amer. Journ. Sci. xxxii. p. 403 (1911) : Phil. Mag', xxii. p. 907 

 (1911). 



