454 
DE. W. M. HICKS: A CEITICAL STUDY OF SPECTEAL SEEIES. 
taking the first two lines as really in the relation indicated, and are thus enabled to 
arrive at the value of F (6). Using B.M.M. measures the separations given by the 
F ( 2 ) lines are their differences from 17081'46 or 94‘88, 323'55 with very small errors 
±‘05. These, therefore, give for P (6) 34336'06±'25 —94‘88 = 3422118±'25 and 
33918’08rk'5+ 323'55 = 34221'63. Both are therefore within error limits of their mean 
34221'40. With this for P (6), and the limit corrected as above to 3185113 the 
value of F (6) is 29460'96. With the value calculated from the formula O — C = — '23. 
As illustrating the way in which D and F sequents are subject to displacements, it 
is interesting to notice that although the separations 94, 323 do not appear as 
directly dependent on F lines after m = 2, they nevertheless occur in the 
neighbourhood. It will be sufficient here only to refer in detail to the case of 
F ( 4 ) = 270U9‘47. At about 50 ahead of this there is a line (6) 27060'60 (W.). With 
this there is the following scheme :— 
267GG-3 (L.D.) 96*6 2G8G3'4 (L.D.) 197-2 (O) 270G0-G0 (W.) 321-4 27382 (L.D.) 
As the L.D. lines are subject, even if correct to the nearest A.U., to equally probable 
eiTors between d\ — ±‘5, or here to dn = ±4, these separations correspond to the 
94'88, and 323'55, whilst 197'2 is the link e. The displacement of 270G0 from F (4) 
may then be in the F sequent or the limit—probably the former, or a, h or c link. 
Tlie existence of the parallel sets, the indications of the associated P types, and 
the nature of the displacements all point to the conclusion that our original series is 
of the F type. Consequently the limit F(oo) = 31851‘13 is a (7 (l) sequent, but 
there is nothing as yet to show whether it belongs to a or a satellite set. If, 
however, we can find a D (l) set the value of .D ( go) can be obtained with sufficient 
accuracy to obtain the values of Aj, Ag and the e link. The further consideration of the 
F series will therefore be postponed until this further information has been obtained. 
It has already been remarked that only the S (2) and D (l) lines in any S or D 
group can be expected within the observed region. A superficial inspection of the 
list of lines shows a very large number of separations in the neighbourhood of 46 
to 49 and about 20, clearly related to v^, v.^ values as they show the normal ratio i/j: v^, 
and are in step with those of the other gases. In about the region in which the 
D lines should be expected Baly gives the strong set (4) 21200'90 49-24 ( 4 ) 21250T4 
with an equally strong line at (4) 21230'! 1 which might be a line to the doublet 
set. Watson, however, gives other strong lines as well, including a triplet. 
These give 
(1) 21156'77 (W.) 48-18 (l) 21204'95 (W.) 
44-13. 45-19 
( 4 ) 21200'90 (B.) 49-24 ( 4 ) 21250'14 (B.) 
(5) -81 (W.) 49-36 (5) '19 (W.) 
29-21 
(5) 21230-11 (B., W.) 
1971 (4) 21224'66 (B., W.) 
