390 DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



7 '63 and 5 '09 but they have not been observed for F(2) -as indeed is the case in 

 Ca and Sr the first set in which show separations of the full amount. The curious 

 dislocation of the second half of the triplet from the first seen in Sr shows itself here 

 also. The analogue appears to be shown in the triplet coming next in the list which 

 appears to have kept its first member and satellite. The displacement is 381'06. 

 This cannot be due to a displacement in F ( oo ), for if so the separations due to 

 15(5, 9$, would be considerably larger. If it is treated as a displacement on VF the 

 denominator difference is 43403-5'3 while 3A 2 + lie? = 43414. It is probably 

 therefore this. The corresponding displacement in Sr was found to be 3A 2 The 

 separation between the first line and the satellite is 575, the satellite being due to 

 LEHMANN whose measures are not very accurate, it may well be 6 '01 corresponding 

 to a satellite difference of S. The lines may therefore be represented 



F U (2)(3A 2 +11<$), F 21 (2)(3A 2 +11<S), F m (2) (3A 2 

 F n (2)(3A 2 



If the next two lines are correctly allocated, 18686 should have an unobserved 

 satellite with a difference 2. This would make 18941 '97 or F 21 260'26 ahead 

 of the satellite, so that this supports the allocation. The line 21308"19 = F n (4) 

 corresponds to a satellite with 58. This makes, on the supposition of satellite 

 differences of 2S, BS, 2156070 or F 22 (4) 260'89 ahead of the satellite F 13 (4), the 

 satellite F 12 (4) being absent. The line for m = 5 appears to be displaced to 22706. 

 The value calculated from the rough formula gives a line 250 behind the strong line 

 22979'57, clearly showing that the latter is a F 2 (5) line, and 22706 is very close to a 

 displacement of A 2 on the calculated. If this be made exact the undisplaced line 

 would be at 22719'97, or 259'60 behind 22979'57. This is within error limits of 260'17. 

 Hence F 13 (5) has been altogether displaced to 22706'84 = F 18 (5) (A 2 ), and 22979 '57 

 is F 2 (5). For m = 6 the formula gives F x (6) = 23582'83. There is a doublet at 

 23667'07 ('28), 23919*27 (114) with a separation 252'20, and no others in the neigh- 

 bourhood. If these are the displaced F (6), the normal F (6) would be 23 59 5 '82 and 

 23855-93 and the observed lines 23667'07 = F x (6) (9A 2 ) and 23919'27 = F 2 (6) (8A a ). 

 The calculated normal lines have separation 260'11, or practically 260'17. A line at 

 23995-83 is 413 = 260+153 ahead of the calculated F, (6). It is therefore the 

 undisplaced F 3 (6). 



There are a large number of other lines clearly related to the F type. Their 

 complete discussion would require a more searching investigation than can be given 

 now. Several sets are related in a manner which is quite common in spark and rich 

 arc spectra, indicated by the fact that a number of lines may differ in succession by 

 nearly the same separation a kind of relation which cannot be due to collateral 

 displacement by equal denominator differences. There are a few also which seem to 

 be attached parasitically to S and D lines. There may be uncertainty also as to 



