Precision-measurements in the X-llay Spectra. 645 



When the lattice-constants for rock-salt log 2d= '7503541 

 (at 18°) and for calcite log 2d = '7823347 as deduced in the 

 earlier paper are used for evaluating these measurements, 

 the folio wing wave -lengths are obtained : — 







Table V 



[. 

 \ x.u. 



Mean. 



PI. 5, 6. 



L a. 2 . 

 La, . 





1484-52 

 1484-51 





PI. 8, 9. 











1484-52 



PI. 5, 0. 



La, ., 





1473-44 

 1473-52 





PI. 8, 9. 











1473-48 



PI. 2, 4. 



In\ . 





1279-15 





Pi. 12, 13. 



L01 • 





1279-19 



1279-17 



PI. 2, 4. 



L0, . 





1241-92 





PL 12 13. 



L/3 2 . 





1241-90 



l°4i-91 



PI. 27-30. 



Lv, . 







1095-53 



The good agreement between the values for the wave- 

 lengths obtained from calcite and from rock-salt strongly 

 supports the accuracy of the lattice-constant of calcite in 

 reference to that of rock-salt. 



As is well known, the L-series consists of three groups of 

 lines a, £>, and <y. The fainter lines of these groups have 

 been measured with, reference to one of the above stronger 

 lines in the same group. Some very faint lines were not 

 measurable in the comparator but were only estimated 

 to /q mm. In the following Table VII. these wave-lengths 

 ■are given to five figures only. 



Table VII. 



Line. A X.U. ^. 



e,l 1675-05 544-02 



a',a 2 1484*2 613-85 



a,a l 1473-48 618-45 



n,v 1417-7 642-78 



v, j3 4 1298-74 701-66 



[1287-1] 708-03 



(3, /3 X 1279-17 712-39 



0, & 1260-00 723-23 



y,j3 2 124191 733-76 



[1239-5] 735-29 



[12205] 746-63 



— [1211-8] 752-00 

 ?,j8 6 1203-1 757-43 



— [1128-4] 807-57 



5, 71 1005-53 831-81 



0, y 2 106584 854'98 



x , 7 " 3 1059-65 859*97 



■^, y 4 1026-47 887'77 



P/m7. Ma?. S. fi. Vol. 38. No. 22; 



X. 



X. 



A. II. Compton. 



E. Dershem. 



1484-6 



1483 



14736 



1472 



— 



1416 



1298-7 



1298 



— 



1287 



1279 2 



1278 



1260-2 



1259 



1242-1 



1242 



1218-7 



1220 



— 



1210 



— 



1129 



109(5-5 



1095 



10653 



1065 



1058-4 



1059 



1025- 1 



1025 



Nov. 1919. 



2 Y 



