768 Mr. H. Pealing on Distribution and Quality of 



the other hand, will penetrate an enormously greater thickness 

 of carbon. It is easy to see that so long as thick radiators 

 are used, the effect of the soft fluorescent radiation from carbon 



will have little or no influence on the value of y^ 1 . 



-L90 

 Carbon also emits, under the influence of a beam of Rontgen 

 rays, very easily absorbed corpuscular rays. It has been 

 shown by a number of investigators that these are absorbed 

 in a few millimetres of air. For this reason no corpuscular 

 rays will reach the measuring electroscope, and so the value 



of y^ observed by experiment does not depend in any way 



J- 90 



on the direct action of this easily absorbed radiation. We 

 shall see later that there is a strong probability that this 

 corpuscular radiation, although very little of it emerges from 

 the radiator, yet produces in the radiator itself another 

 radiation in appreciable quantities. This we shall call an 

 " extra " radiation. 



III. Theory of the Absorbability of the Secondary Radiation 

 from Carbon. 

 In many of the experiments very penetrating beams were 

 used, so that we may reasonably expect that the very pene- 

 trating fluorescent radiation will be present in the secondary 

 beam excited by them. The presence of the hard radiation 

 should very considerably modify the absorbability of the 

 secondary radiation emitted. The scattered radiation from 

 the carbon is of the same penetrating power as the primary 

 which excites it. Thus the secondary beam emitted by a 

 very thin sheet of carbon will be of the same penetrating 

 power as the primary, when that primary is very soft, because 

 the secondary radiation is wholly scattered and any soft 

 fluorescent radiation which is excited will not reach the 

 measuring electroscope. As the primary beam becomes harder, 

 the very hard portions may be slightly harder than the hard 

 fluorescent carbon radiation. In this case these hard portions 

 will excite the fluorescent radiation. The secondary beam 

 emitted will then consist of the scattered radiation which, 

 although it is softer than the hardest portion of the primary, 

 will yet be very considerably harder than the primary beam 

 taken as a whole. These two components, the one just as 

 penetrating, and the other much harder than the primary, will 

 together give a secondary beam harder than the primary 

 exciting it. As the primary beam is made harder the 

 secondary beam should be much harder. The percentage 

 difference in hardness will depend on the transformation 



