634 Mr. R. D. Kleeman on the Secondary Cathode 



The relative amount of radiation emitted per second per c.c. of a 

 substance when exposed to the y rays is independent of ja 

 and k, and therefore given by K x simply. The radiation 

 emitted per c.c. when the substance is exposed to the ft rays 

 is given by K 2 = //<#. The number of electrons ejected per 

 atom is given by 



M 



_ R^^l — *Q(2— /g + 2 \/1-k) 



in the case of: 7 rays, and by M 2 = — ^— - in the case of ft rays. 

 The ratio of M x to M 2 is given by 



Mi 



M, 



Rx QL — tt)(2-tt + 2 Vl- ft) 



41— ie+yrz^) 



an equation which does not contain /jl. 



It remains to describe the method by means of which the 

 radiating power of aluminium was determined corresponding 

 to a difference of 800 in the radiating powers of lead and 

 aluminium. The adjustable table was removed and also the 

 wire gauze from the bottom of the aluminium chamber. The 

 lead and aluminium plates used as radiators were each of the 

 same dimensions as the plate c. The radiating plate was 

 kept in contact with the edges of the opening of the aluminium 

 box. Fig. 3 shows the modified part of the apparatus. 



Fisr. 3. 



t3ZE2ZH22Z2EZZZZZZZZZZZZZ22ZZZZZ ZZZZZ2ZZ2i 



Leaks were taken with the aluminium and the lead plate, 

 and a sheet of thin tissue-paper, used successively as radiators, 

 the tissue-paper being stretched tightly over a metal frame 

 enclosing an area somewhat greater than that enclosed by the 

 edges of the aluminium box. All objects near the opening 

 of the aluminium box were removed, in order to reduce to a 

 minimum (when the tissue-paper was used as radiator), the 

 amount of ionization caused by the secondary radiation 

 from surrounding objects penetrating the tissue-paper and 



