Reflexion of the fi-P articles by Matter. 861 



deposits of thorium or of radium emanation, the percentage 

 of the reflected /3-particles rose to a maximum but finally 

 decreased. The results with the thorium active deposit are 

 given in Table VI. and shown graphically in fig. 4. 



Table VI. 

 Thorium active deposit. 



Aluminium 



Percentage of 



in mms. 



reflected /3-particles. 



0-045 



65-3 



•104 



77-0 



•163 



796 



•222 



800 



•340 



760 



•399 



74-0 



•458 



73-0 



•635 



71-0 



The first column gives the absorbing aluminium in mms.. 

 and the second column gives the percentage of reflected 

 /3-particles. 



Fig. 4. 



•oio 



•0?0 '030 -040 -050 -060 



Thickness of /?lum/n/um //v cms 



070 



This decrease may be due to one of two possible factors, 

 viz., either the softer reflected rays are absorbed more than 

 is accounted for by the correction or the amount of reflexion, 

 as measured by the ionization, increases with the velocity of 

 the /3-particles only up to a certain velocity, after which it 

 decreases again. Since this investigation deals with the 

 heterogeneous rays from radioactive bodies, and not with the 

 pure rays of any one velocity, this point cannot be answered 

 here definitely. Investigation of this special phase of the 

 problem is, however, now in progress (see following paper 

 by Kovarik and W. Wilson) . 



