and the Theory of Atomic Structure. 



1073 



into two types, a-levels and ^-levels, in such a way that 

 every observed line appears as a combination of one a- and 

 one 5-level, while combinations of two a- or two 5-levels do 

 not appear *.. It will be seen, that in consequence of the 

 latter rule we never observe lines, the frequencies of which 

 are the exact sum or difference of the frequencies of two 



Diagram I. — Niton. 



S-i 



isH 





& 



''Z 



Mr 

 Mz- 

 : Mr 



Mi- 

 Ms - 



Att 



i Li 



1 I I I 1 I . I 



« T 



U 



KwMA 



__L 



■h 6, 



■b s 3 



■a 4,, 

 •a if, 



■a, Jf X 



■6 3 t 



-a Z, 



■i ;, 



other lines. An illustration of this classification of the 

 X-ray spectra is given in diagram I. for niton, which is based 



* It should be mentioned that some very weak lines have been ob- 

 served which represent a transition b-*~b. They are the transition L 3 -K 

 observed only for W by Duane and Stenstrom and the lines L/3 9 

 (transition M 1 -L 3 ) and Lj3 10 (transition M 2 -L 3 ) observed by several 

 authors for various elements. (See Zeitschr. f. Phys. ii. p. 200, table 9.) 



Phil. Mag. S. 5. Vol. 43. No. 258. June 1922. 3 Z 



