﻿554 



Mr. D. Coster on the Spectra of X-rays 



no emission-lines are found in the same place, and, again, it 

 seems to be only suitable for a definite range of wave- 

 lengths. 



§ 6. The faint lines lying on the short wave-length side of 

 /5 2 gave a great deal of trouble. The photographs of the 

 elements W, Ta, and Lu, as well as those of the elements 

 Sb-Ag, showed that we have to expect 4 or 5 lines in this 

 region. For the elements Er-Sb, however, these lines lie 

 very near to one another (they all fall in a. length of less 



Table XIX. 

 Wave-lengths. 



(&) 



47 Ag 



48Cd 



49In 3317 



50 Sn | 3149 



51 Sb (ftj- 



55 Cs 2480 



56 Ba 23756 



57La 2270 



58 Ce 2176-3 



59 Pr 2087-4 



60 Nd 2004-3 



62 Sm 1852-3 



63Eu 1784 



i64(4d 1719-6 



; 65Tb 1655-8 



i66Dy 15957 



68Er 14892 



71 Lu 1345-9 



73Ta 1260-0 



74 W 12208 



3620 



3259-8 



3108-1 



2965-8 



2473 



2371-2 



2277 



2184-0 



2095-8 



2011-7 



1858-1 



1788 



(&) 



1482-3 

 13330 

 1242-9 

 1202-1 



3630 



3266-8 



3114-4 



2972-5 



2285 



2191-6 



2102-5 



2019-3 



1865-7 



1796 



1728-1 



1664 



(£) 



1339-8 

 1250-6 

 1209-4 



0M 



3663-3 



3477-5 



3304-0 



3142-6 



•J993-4 

 2483 

 2381-7 

 OS.,/8,0) 



(3 10 ) 



3653-7 

 3468-4 

 3295-9 

 3134-7 



2985-8 



1501-4 

 1359 

 1273-8 

 1235-4 



than 1 mm. of the plate), so that we may assume that they 

 must coincide or cross in several cases. This made the 

 classification of the lines a very complicated puzzle. Several 

 solutions of it have been tried, that which seems to be the 

 best is given in Tables XIX. and XX. 



The following facts support this classification. It has 

 been assumed that the line fi b does not occur in this region 

 under the conditions of the experiments, for the following- 

 reasons. For the elements in the neighbourhood <rf W it 

 was shown * that 8 b and the L x discontinuity nearly coincide. 

 For the elements from Eu (63) to Cs (55) the Li absorption 

 discontinuity was obtained on the plate as a white line on a 



* D. Coster, Phys. Rev. xix. p. 20 (1922). 



