1126 On X-ray Electrons. 



for so bold a line; moreover, its intensity is greater than 

 the HhKjS radiation should give *. 



II. A point which is not brought out in the table and 

 which should be mentioned is that the electron emission 

 increases as the atomic number increases. In fact, the time 

 of exposure necessary to produce a photograph of a certain 

 intensity is very roughly inversely proportional to the 

 atomic number. With the elements of higher atomic 

 number, also, there is a very considerable amount of 

 continuous spectrum, due possibly to the preponderating 

 importance of X-ray electrons ejected by the " white " 

 radiation from the target. 



III. It is clear from reference to the copper X-ray 

 electron spectrum that, although each line shows a more 

 or less sharply-defined head or boundary on the high- 

 velocity side, }^et there is in addition more than a suggestion 

 of breadth. Measured in terms of equivalent frequency, 

 this breadth is explicable on the supposition that these 

 lines are really doublets, unresolved by the apparatus and 

 separated approximately by frequency M. 



IV. It is to be noticed finally that whenever a frequency 

 difference less than that corresponding to the K (or L as 

 the case may be) might have been expected, no corre- 

 sponding line is observed. Thus, in the arsenic spectrum 

 RhK a -AsK = 202, which is less than AsK = 288, and 

 no line appears at 202 ; or, again, in the bismuth spectrum 

 RhK a — BiL — 91, which is less than BiL = 399, and no line 

 appears at 91. 



Further, although the L electron lines are strong in the 

 cases of tungsten and bismuth when the K electrons are 

 not disturbed, yet in other cases — copper, for example — no 

 trace of L electrons could be found, although a careful 

 search for them was made. 



Experiments are being continued. 



My thanks are due to the Government Grant Committee 

 of the Royal Society for assistance in defraying the cost of 

 the quartz apparatus. 



The University of Leed>, 

 April 3rd, 1922. 



* Zinc impurity in the copper-leaf would reduce the discrepancy 

 somewhat, but hardly sufficiently. Whatever the explanation — and 

 further experiment is in progress — it may be pointed out that the 

 triplet (270, 287, 313) is complementary member for member with 

 (217, 193, 172), in the sense that when corresponding members are 

 added together the total approximates closely to 490 (RhK a ). 



