Homogeneous Corpuscular Radiation. 355 



probable that the emission of corpuscular radiation in these 

 cases is connected with the scattering o£ the homogeneous 

 exciting radiation. 



In this connexion it is interesting to note that during some 

 experiments carried out in conjunction with Dr. Barkla*, 

 upon the scattering of an ordinary primary beam by different 

 substances, it was found that silver behaved as a much more 

 efficient scatterer than light elements such as carbon or 

 aluminium. For equal quantities of matter traversed, the 

 silver proved to be about 6'5 times as efficient a scatterer as 

 carbon or aluminium. jSTo determination has, however, yet 

 been made of the relative scattering of homogeneous beams 

 of different penetrating powers. It is, however, significant 

 that in the cases where there is no production of the Rontgen 

 radiation characteristic of either aluminium or silver, the 

 corpuscular radiation from the latter is invariably greater than 

 from the former. The ratio of the corpuscular radiation from 

 silver to that from aluminium diminishes from about 15 for 

 very soft secondary exciting beams to a little over 2 for the 

 hard secondary beam from silver. 



Experiments are at present in progress to determine in 

 what manner the scattering of homogeneous Rontgen radiation 

 by different substances takes place. It is hoped that the 

 results of these experiments will throw additional light upon 

 this part of the subject. 



Perhaps the most striking result of the present investigation 

 is the entire dependence of the corpuscles for their velocity 

 upon the " hardness " of the Rontgen radiation used to excite 

 them, and their independence of the kind of metal from 

 which they are produced. This is in marked contrast to the 

 Rontgen radiation characteristic of a metal. This latter is of 

 constant penetrating power, and this penetrating power 

 depends solely upon the metal from which it is produced, 

 and not at all upon the hardness of the Rontgen radiation 

 producing it. Thus as far as the absorbability of these two 

 types of radiation is concerned, we see that in one case the 

 exciting radiation is the controlling factor, while in the 

 other the radiator emitting the radiation itself furnishes 

 the control. 



The variations in the intensity of the corpuscular and 

 Rontgen radiations appear to follow similar laws, but the 

 evidence is far from being complete. 



A fuller discussion of the foreoomo- results, including those 

 on the scattered radiation, will be attempted in a further paper. 



* Barkla and Sadler, Phil. Mag-. Oct. 1908, pp. 550-584. 

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