X-Rays and the Atomic Weight of Nickel. 413 



the same substance, appears to be entirely absent in the case 

 o£ these secondary rays. 



That this is on account of the homogeneity of the beam 

 before traversing the plates seems highly probable. 



We are thus able to determine what are true absorption 

 coefficients for these secondary rays by various substances. 



These have been calculated and are given for two distinct 

 series of observations in the following table. In the first 

 series the radiators were experimented upon in the order 

 zinc to iron, and in the second series from iron to zinc. 



No attempt has been made to allow for the slight obliquity 

 of some of the rays in traversing the plates, as the conditions 

 were similar in all the experiments. 



The values given are probably as a consequence 2 or 3 per 

 cent, too high. 



Table I. 



Radiator. 



Absorber. 



Zinc 



Al. 



Fe. 



Cu. 



Zn. Ag. Sn. 



Pt. 



970 

 121-3 

 147-3 

 175-0 

 216-0 



96-6 



1198 

 146-9 

 177*5 



218-2 



1073 



1159 



1229 



480 



510 



1063 



1159 



1170 



471 



529 



514 

 367 

 610 

 731 

 905 



512 

 483 

 596 

 745 

 975 



342 1930 | 1656 

 416 2340 J 1992 

 513 2836 1 2383 

 625 3456 2890 

 789 4050 3500 



358 1960 ' 1636 

 434 2324 1931 

 525 2802 2430 

 632 3360 2904 



804 4020 ! 3470 



i 



3550 

 4270 ' 

 5210 

 5970 

 6520 



2422 



4170 

 5140 

 6080 

 6820 



Copper ... 



Nickel 



Cobalt 



Iron 



Zinc 



Copper 



Nickel 



Cobalt 



Iron 





From these results, plotted in figs. 3 and 4, it is seen that 

 the relation between absorption coefficient for a secondary 

 radiation and atomic weight of the radiating substance is 

 almost perfectly a linear one within this range of atomic 

 weights for most absorbing substances. The exceptions were 

 iron and copper, which, it should be observed, were among 

 the radiating substances experimented upon. 



The values for the atomic weight of nickel obtained by 

 interpolation of the absorption of its radiation on the curves 

 for the absorbing substances aluminium, zinc, silver, tin, and 

 platinum were 61*35, 61*6, 61*45, 61*6, 61*15 respectively, 

 from the first series of experiments. The corresponding 

 values obtained from the second series in which the radiating 



Phil. Mag. S. 6. Vol. 14. No. 81. Sept. 1907. 2 F 



