Asymmetric Emission of Secondary Rays. 145 



that on the incident side. A similar asymmetry in the 

 distribution of the X type of secondary rays produced by 

 the absorption or stoppage of Rontgen, 7, ft, and cathode 

 rays has been demonstrated by the experiments of Bragg 

 and his pupils, and of Kaye, Stark, Crowther, Gray, and 

 other investigators. 



This type of effect was first predicted by Bragg as a 

 consequence of his view that the 7 and Rontgen rays were 

 uncharged material particles in rapid motion, and its 

 existence has consequently been held to favour Bragg's 

 theory. The occurrence of similar effects with light would, 

 by a like argument, lead to the conclusion that it also 

 consists of a shower of material particles. In fact, the 

 greater number of Bragg's reasons for favouring the 

 material constitution of 7 and Rontgen rays apply also to 

 light. Most writers seem to accept the principle that light 

 and X radiations, as it is convenient to call radiations which 

 behave physically in a manner similar to the 7 and Rontgen 

 rays, differ only in degree and not in kind. The explanation 

 then usually offered * to account for these asymmetric 

 effects in secondary emission is that the energy in the 

 radiations is not continuously distributed, but exists in a 

 very concentrated form in limited regions. In this way a 

 single electron may be made to receive the major part of 

 both the energy and momentum in a radiation unit. As the 

 case against such a view of the nature of light is at least 

 arguable, it is worth while to examine the question from a 

 rather wider standpoint, to see if an estimate of the 

 maximum effects to be observed may be obtained without 

 making any definite hypothesis about the structure of the 

 radiation. I shall practically confine myself to the secondary 

 emission of electrons under the influence of radiations of the 

 X type and light. 



A general review of the phenomena grouped under the 

 emission of electrons caused by radiation and under the 

 temperature variation of the radiation from a black body, 

 supports the view that the action between the radiation and 

 the matter is primarily between radiation and electrons, and 

 that. this action goes on in a manner which may be treated 

 as continuous, in the case of any particular, electron, until 

 the latter reaches a certain condition. This condition is 

 followed by an act of a different character, which we may 

 term disruption ; the act of disruption terminates the con- 

 tinuity of the preceding processes and is succeeded by a new 



* Stark, Phys. Zeits. vol. x. p. 579 (1909). 

 Phil. Mag. S. 6. Vol. 25. No. 145. Jan. 1913. L 



