646 Precision-measurements in the X-Ray Spectra. 



In the 4th column are given the values of A. H. Compton* 

 calculated from the reflexion-angles with the above lattice- 

 constant instead o£ that used by Compton. The agreement 

 is surprisingly good, as Compton only estimates his angles 

 to be exact within 0''5 (tor the stronger lines). A com- 

 parison of our values shows that the probable errors in 

 the measurements of Compton are only about 0'*1. It 

 may be remarked that Compton uses a registrating spectro- 

 graph on the ionization method, whereas our measurements 

 are based on a photographical method. 



In the next column are tabulated the wave-lengths of 

 E. JDershemf. These measurements are not of the same 

 exactitude as the former, but in compensation therefor 

 some fainter lines have been found. Two lines (I, /3 5 ) 

 which certainly belong to the L-group of tungsten are 

 missing. Some of the other fainter lines have also been 

 refound on my spectrograms. Whether they belong to 

 the tungsten spectrum is still open. Besides the values 

 in Table VII., Dershem grves the wave-lengths 1177, 1071, 

 1043. Of these, the first probably is the Pb-L a-line. 



In some interesting papers Sommerfeld J has given 

 evidence to show that the L-series can be separated into 

 two groups with constant frequency-differences between 

 the lines. The present measurements show that there is a 

 rather good agreement between the values of the first group, 

 but that there is only approximately the same frequency- 

 difference. In the 3rd column of Table VII. are gi/en the 



values of p, where R stands for the Pydberg constant. Prom 



these values we find the following frequency-differences: — 



Table VIII. 



6-i) = l-i) = 98-76 



j3- a' = P x -a 2 = 98-54 



8-y = y 1 -/3 2 = 98-05 



9~Z = y 2 - -ft = 97-55 



It seems from this table that the difference decreases with 

 decreasing wave-lengths. 



Lund, Physical Laboratory, 

 .Time 1919. 



* A. H. Compton, Phvs. Rev. June 191G. 



t E. Dershem, Phvs. Rev. 1918. 



X A. Sommerfeld. Ann. d. Phys. li. up. I, 125 (1916). 



