﻿560 Mr. D. Coster on the Spectra of X-rays 



fairly sharp line. Since in the elements Ta-Er, for which 

 y 10 is not present, a change in the relative intensity of y 2 was 

 already observed, it appears that this change in intensity 

 cannot be interpreted as being connected with the presence 

 of y 10 . For Te and the elements with lower atomic number 

 72 can no longer be separated from y 8 . It is difficult to say 

 whether y 10 still exists for these elements or not, but it seems 

 to be hardly probable. 



For the elements Sin- Eu a faint line was observed on the 

 short wave-length side of ft. The presence of /5 4 in this 

 place made it impossible to study this line for the elements 

 with lower atomic number than Sm, and in the same way 

 the presence of /3 6 made measurements impossible for 

 elements with higher atomic number than 68. It may 

 be that this line is the same as /3 13 previously measured 

 for the elements Pb-Sb— its wave-lengths are given in 

 Table XXIII. 



Part V. 



Comparison of the new Experimental Results with 

 Bohr's Theory. 



§ 1. The L-series of most of the elements from lib (37) to 

 U (92) has now been thoroughly investigated by the author*, 

 working in the laboratory of Prof. Siegbahn ; and from this 

 work it appears that the same simple laws which have been 

 dealt with in Part I. govern the emission of the X-ray 

 spectra of the elements from U down to Pb. There are still 

 some lacunaa in my tables, but these have no particular 

 meaning, as it should only be a matter of patience and time 

 to fill them. Some rather faint lines were overlapped by 

 sharper and more intense lines of the same or another 

 element, making measurement very difficult. Of some ele- 

 ments no suitable specimens were available, some elements 

 gave difficulties due to their high vapour pressure. In this 

 connexion it may be pointed out that the L-spectrum of 

 mercury has been measured in a very ingenious way by 

 Mr. Miillert ; most of his results agree very well with ours. 



The L-spectrum of tungsten has been measured by several 

 authors with essentially the same results. In addition, 

 Dauvillier % has measured the L-spectrum of U, Au, Pt, Ir, 



* As has been stated above, for the measurements of the elements 

 Rb-Ta, use was made of the precision measurements of the strongest lines 

 of these elements done by Hjalmar, and for W Siegbahn's precision 

 measurements were used. For the wave-length tables of Ta-U, see 

 1). Coster, Zeitschr. f. Phys. vi f p. 185 (1921). 



t Miiller, Phil. Mag. xlii. p. 419 (1921). 



% Dauvillier, Comptes Rendus, clxxiii. pp. 647, 1458 (1921). 



