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XVI. Higli- frequency Spectra and the Periodic Table. 

 By Prof. W. M. Hicks, F.R.S* 



TI1HE decisive importance in questions affecting the periodic 

 JL table of Moseley's law governing the high-frequency 

 spectra of the elements must be generally acknowledged, and 

 any discrepancy therefore between it and the ordinarily 

 accepted view of the constitution of the table requires 

 careful consideration. Such a discrepancy appears in the 

 interval between Ce and Yb. These elements have their 

 position in the table definitely settled by their chemical pro- 

 perties, and the generally accepted constitution of the table 

 gives 16 spaces to be filled between them. The atomic 

 numbers, however, as determined by Moseley give 58 for Ce 

 and 71 for Yb, leaving therefore only 12 spaces. Or to put 

 it in another way, if the 16 spaces are accepted as actually 

 existing, the atomic numbers place Yb in the 01 group, Ta 

 amongst the Alkalis, and W between Cd and Hg, thus up- 

 setting all chemical similarities. It is clear that both cannot 

 be correct. One way of explaining the difference would be 

 to suppose that the L series splits up into two at some 

 element between Nd and Yb, and that the new formula 

 depends on (N — 3) 2 in place of (N — 7) 2 . In connexion with 

 this it is interesting to note that there appears to be some 

 disturbance in Moseley's curve in this region. But a better 

 explanation would appear to be that Moseley's rule is abso- 

 lute, and that as a fact there are only 12 spaces between Ce 

 and Yb. Some strong independent evidence in favour of 

 this view is found in a recent discussion by J. R. Rydberg 

 on the system of the elements f- He identifies each element 

 by the integral number oivino- its place in the table, regarding 

 this as the "independent variable/' functions of which must 

 give all the properties of the atom. For a reason given 

 below this number is two units above that chosen by Moseley 

 for the " atomic number." 



Starting from the acknowledged facts as to the two short 

 series or. 8 elements each, followed by two long series of 16 

 each, he supposes the table to be built up of long series con- 

 taining 4p 2 elements. Thus the two short series He through 

 Ne to A make one long of 16 elements (p — 2). The two 

 recognized long series A through Kr to Xe make one long 

 one of 06 elements (p = 3). He then supposes to succeed a 



* Communicated by tue Author. 



t Lunds Universitets Arsskrift, N. F. Afd. 2, Bd. ix. Nr. 18, or 

 Kongl. Fysiografiska Sallskapets Handlingar, N. F. Bd. xxiv. Nr. 18. 



