8 ROYAL SOCIETY OF CANADA 



striking a solid bod}' cause the ejection only of some of those corpuscles 

 which have velocities in their orbit or free path approximating to those 

 of the corpuscles which first gave rise to the ether pulses. 



One fundamental difficulty arises in writing on secondary radiation. 

 The investigations of H. W. Schmidt/ and of Crowther/ indicate that 

 secondary kathode radiation consists mainly, or entirely, of scattered 

 primary rays, for they have proved that /? particles, in passing through 

 matter, lose little or no velocity and are diffusely scattered. On the 

 other hand, Kleeman and others in treating of secondary rays due to 

 primary y rays writes of " electrons ejected by y rays." Now the 

 electrons which constitute the secondary kathode radiation, due to fi 

 and to y rays respectively, have nearly equal velocities, and it seems 

 unreasonable to suppose that in the one case we have scattered primary 

 and in the other case electrons ejected from the atoms of the secondary 

 radiator. It must be admitted that Bragg's theory of the close 

 similarity of (5 and y rays — the difference being the important one of 

 charge — removes all these difficulties as far as secondary radiation is 

 concerned. Nor does this theory seem more complicated than the con- 

 ception of an ether pulse with discreet centres of energy on the surface 

 of the spherical shell of the ether pulse. But apparently other dif- 

 ficulties arise. Again, H. Starke, in Le Radium for February, 1908, 

 finds that /ï rays striking a solid do not give rise to secondary y rays, 

 and my observations tend in that direction also, for the secondary y 

 rays appear to be caused solely by the primary y rays. Nevertheless, 

 it is remarkable that the impact of kathode rays should give rise to X 

 rays, and that the impact of fi rays should not give rise to y rays. 

 However, we have no knowledge of the effect of concentration of the 

 impact of /3 rays. As matters stand at present the most notable 

 difference between X and y rays is that the former arise when the 

 kathode rays are stopped or absorbed, and the latter where the ft 

 rays originate. 



The following experiments show clearly that primary y rays give 

 rise to secondary y rays, that the intensity depends upon the material 

 surrounding the radium employed, upon the nature of the secondary 

 radiator, upon the thickness and material of the screens placed in 

 front of the electroscope, and that the intensity of the secondary y 

 radiation does not follow the order of the atomic weight, or of the 

 density, of the secondary radiator. In all these particulars there is a 

 similarity between secondary X and secondary y rays, and this ac- 



' Phys. Zeit., June 1907. 

 2 Le Radium, March 1908. 



