and the Theory of Atomic Structure. 1105 



to Ba, but that these shells materially change for the 

 elements with lower atomic number than Ba. 



My researches in the L-series of the rare earths above 

 quoted seem also to offer strong arguments in favour of 

 Bohr's theory. The lines in the L-series, which are connected 

 with N-levels, are : {3 2 , 71, 73, 72, /3 6 and y 5 . Now for some 

 of these lines remarkable anomalies of a new type were 

 found. For both the lines j3 2 and 7! rather faint satellites 

 were observed at some distance on the long wave-length 

 side *. Though we cannot yet account for this phenomenon, 

 we should according to the theory expect some irregu- 

 larities just in this region, accompanying the gradual 

 transformation of the N-shell during the completion of the 

 electronic configuration of 4-quantum orbits. For the 

 lines 72 and y 3 an analogous phenomenon was observed. As 

 these lines lie very near to one another, it is somewhat 

 difficult to interpret the photographs. The lines /3 6 and 75 

 however, which are not very strong, seem to show no 

 irregularities at all. More experimental data will soon be 

 published. 



§ 9. It is a fact well known to every one who has worked 

 some time in X-ray spectroscopy, that on nearly every 

 photograph taken of the X-ray spectrum of a single element 

 there are found some lines which cannot be classified. It 

 is probable that in most cases these lines are due to some 

 other element, and very often this may actually be proved. 

 The lines in the K-series ol elements of hio-her atomic 

 number, however, have not yet systematically been measured. 

 If these lines appear in higher order on the plate, the 

 identification will be impossible. 



On the other hand, we must reckon with the possibility 

 that some of the " unknown " lines really belong to the 

 investigated element in question. In this case we must 

 assume that the appearance of these non-systematic lines 

 depends on special conditions, which are only fulfilled for 

 one or very few elements. It appears from these con- 

 siderations that conclusions which are based upon measure- 

 ments of only one element have no great value for other 

 elements. 



There are several lines which cannot be inserted in such 

 simple diagrams as I, II, and III, but which are found for 



* The other lines which cannot be inserted in a simple diagram lie 

 always on the short wave-length side of a line with which they seem to 

 be in some way connected. 



Phil. Mag. S. 6. Vol 43. No. 258. June 1922. 4 B 



