140 



MR. G. W. C. KAYE ON THE 



as mentioned above, claim a higher atomic weight 6 1 '4 for nickel than the value 

 587 to which chemists give acceptance. The evidence the latter offer for the atomic 

 weights of both nickel and cobalt (59) is so strong, that one hesitates to accept so big 

 a change as Messrs. BARKLA and SADLER suggest. Their contention seems to rest on 

 the following experiment. The secondary Kontgen radiations from Fe, Ni, Co, Cu, 

 and Zn were cut down by a single screen of each of the following metals : Al, Fe, 

 Cu, Zn, Ag, Sn, and Pt. The percentage absorptions were plotted against the atomic 

 weights of the radiators, and the points for the same screen were joined by a smooth 

 curve (fig. 1, p. 410 in their paper). 



2-0 



OOO5".cf, 

 TH/CKHESS or PT SCft/V 



Fig. 9. Pt screen, 20,000 volts. 



The curves for five of these screens indicate a value about 61*4 for the atomic 

 weight of the nickel radiator ; the curves for the other two screens (Cu and Fe) which 

 exhibit selective transmission are not used. It is noteworthy that four of the five 

 screens (Al, Ag, Sn, and Pt) have thicknesses which produce roughly the same 

 amounts of absorption of the different radiations, so that any anomaly affecting the 

 one screen might perhaps be expected to occur with the other three. 



The rest of the paper deals mainly with absorption coefficients and " transparencies." 

 These data are calculated from results obtained as above, by assuming the homogeneity 

 of the different secondary beams a general assumption admitted by the authors 

 themselves to be dubious (p. 421). 



I venture to suggest, on the lines of the results obtained in the present research on 



