﻿386 Mr. J. A. Crowther on the Coefficient of 



coinciding with the second long period; while barium, 

 obviously on still another division of the curve, is the only 



Fig. 3. 























































A 



























T 



























P " 



























f 



? 















r/V 







u 



























/■ 



371 















4 U 



























i, 



s? 



K 



/ 



i 







3a. 







































/ 







-n 



i, 



































s 



lA 



* 



t^' 



f cu 



71 













































u 















































b, 



I 



rVa 































































































































































































































































10 SO 30 40 50 60 70 80 90 tOO 110 120 130 140 150 160 170 180 190 200 210 220 230 240 

 /I TOM I C WE /GUT 



representative of the third. The fourth long period is some- 

 what poorly represented by platinum, gold, and lead, but 

 sufficient is shown of the curve to prove that this section is 

 distinct from and similar to the previous sections. Uranium 

 is the only representative of the fifth long period, and a fifth 

 portion of the curve. It is interesting to note in passing, 

 that the absorption by uranium of the uranium $ rays is 

 in no way exceptional, the coefficient of absorption being 

 quite what might be expected from an element of its atomic 

 weight. 



Again, the different sections of the curve are very similar 

 in appearance, if we exclude the first short period, which is 

 also somewhat exceptional in character chemically. Each 

 commences with a nearly horizontal portion, and then rises 

 sharply up to a maximum. Practically the whole of the 

 increase occurs in the second half of the long periods. 



It will be noticed also that similar elements occur on similar 

 portions of the curve. Thus the alkali and alkali earth 

 metals come at the commencement of the different sections ; 

 the metals of the eighth group come in similar positions 

 near the minima ; while the sulphur, selenium, and tellurium 

 group, and the halogens form the maxima. 



In brief, it appears evident that the ratio \fp, measuring 

 the absorption per corpuscle, is not a constant, but is a 

 periodic function of the atomic weight ; the periods corre- 

 sponding exactly with those of the chemical classification. 



