w 



Precision-measurements in the X-Ray Spectra. 600 

 Av H = 0-3645 ± 0-0045 

 tth «- = 5-3146 . 10-\ 



The value of the wave-length-difference in the X-ray 

 spectrum of Cu as determined from the plates 4 and 5 is 



A\ = [0-00379 ± 0-00004] 10- 8 , 



which gives /XT " g% . =0-379 + 0-004 



n (N-3-o) 4 - 



with N = 29. The right member of the above equation (1) 

 has the value 



Av H ' [ ] =0-3645 + 0*0079 4- 0-0003 



= 0-373 ± 0-005, 



which shows a complete agreement with the empirical va 

 The further examination of this question with other elem 



alue. 

 jments 



has led to surprising results, which require further inves- 

 tigations. These are now going on and will soon be 

 published. 



Another interesting consequence of the theory of Sommer- 

 feld has been briefly pointed out in a note * to the Bavarian 

 Academy of Science. It deals with fine structure of the 

 /8-line, which had previously been regarded as simple. This 

 line arises when an electron runs from the third to the first 

 ring. But as the intermediate second ring will be somewhat 

 affected through the variation of the system, the change in 

 its energy will also have a little influence on the frequency 

 of the line. The double nature of this ring will therefore 

 necessarily cause the /3-line to appear as a doublet. The 

 theory also shows that the frequency-difference between the 

 two lines of this doublet will be more remarkable in the 

 case of elements with smaller atomic weights, and that the 

 weaker component will have the greater wave-length. 



All these predictions of the theory were in the best 

 accordance with the empirical results. In fact, the author 

 has, without any knowledge of these theoretical results, on 

 the spectrograms of Ni and Co, observed the expected effect 

 (see the concluding remarks in the cit. note). 



Some preliminary values for the frequency-difference in 

 this doublet [/3, /3'] are given in the following table, which 

 will soon be completed : — 



* Sommerfeld, Sitz. Ber. d. Bayr. Akad. d. Wiss. (June 1918). 



