10!' 8 Mr. D. Coster on the Spectra oj X-rays 



by the aluminium sheet (the reproduction does not give a 

 very good impression of this fact). It is quite possible that 

 it is the tungsten L^ in the 6th order. 



In the same way I was able to show that the transition 

 L 2 L X does not exist ; this, however, is what we should already 

 expect from the a-b rule. 



Part III. 



Discussion of Results. 



§ 1. As has been stated in Part II. § 1, the object of this 

 paper is to compare the changes in the characteristic X-ray 

 spectrum as the atomic number decreases with the changes 

 in the structure of the atom as given by Bohr's theory, of 

 which a brief account has been given in Part I. In order to 

 do this, we will deal wirh the diagrams of the energy levels 

 or the inert gases, which are based upon measurements of 

 the elements preceding or following the inert oases in the 

 periodic table. For niton the diagram has already been 

 given in Part I. of this paper. 



As regards this diagram, the following remarks may here 

 be made. Only the lines belonging to the L-series have 

 been systematically investigated for the elements in the 

 neighbourhood of niton *. The complexity of the line L 4 

 which is suggested by analogy with the appearance of the 

 pairs of lines L/3 3 ~L/3 4 and LY3-Ly 2 could not be proved 

 experimentally, because of the small difference of energy 

 between the levels 3 and 4 . The energy-difference between 

 the levels 1 and 2 could not be obtained experimentally 

 for the same reason. As yet there is no experimental 

 evidence for the existence of the three P-levels inserted in 

 the diagram. Perhaps the line 568'9 found by Dauvillier f 

 in the spectrum of U represents a transition P^L^. But 

 since in general it is very dangerous to draw conclusions 

 from the measurements of only one element, it seems better 

 to postpone a discussion of the P-levels until a thorough 

 investigation of the X-ray spectrum of the radioactive 

 elements has been made. The K-spectrum of the elements 

 ■ in the region of high atomic number has been measured with 

 sufficient accuracy for W only. But also different measure- 

 ments of the K-series, made by several authors for elements 

 of lower atomic number, support the arrangement of lines 



* See D. Coster, Zeitschrift f. Physik, iv. p. 178 (1921) and I. and II. 

 In I. and II. the arguments are given in favour of the arrangement of 

 the lines in the diagram 1. 



t Comptes Rendus, elxxii. p. 1350 (1921). 



