DK. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 421 
liiTZ Combinations .—The results obtained enalde us to test for additional series, 
associated with the name of Ritz who first pointed out their existence. Tliey are 
represented by the expressions n = p (1)-/ {m), and s[l)-f (m). Here p (I) = S { oo) 
= 5I025‘30 and/( 7 u) is given by the formula on (p. 412). s (l) = P ( oo) = 93178’69 
and should give a parallel series 42I53‘39 ahead, and therefore in the extreme ultra¬ 
violet. The results are for the sets Pi, P 2 , P 3 . 
7n. 
Calc. Pi -/ (m). dX. 
Observed. 
0 
38665*21 -*07 
(1) 38666*56 
1784*06 
(2) 40450*62 
806*91 
(1) 41257*53 
3. 
44105*93 *18. 
(44102*34) 
1783*08 
(45885*42) 
815*66 
(46701*08) 
4. 
46607*42 *03 
(46606*52) 
1784*28 
(48390*80) 
807*29 
(49198*09) 
5. 
47961*81 *06 
(47960*42) 
1777*90 
+ 813*68 
(50552*00) 
Notes.—m = 2. 1784-06-f806'91 = 1777'90 +813‘07 
^ — 3- There is some ambiguity as to F 3 (3), which gives the calculated value. 
The deduced ultra-violet lines are from the observed triplet by the e link. 
(7) 36788-24 1783*08 ( 2 ) 38571-32 805*66 (l) 39386*98. 
Also 
e-!-'y + (l) 32362*98 1777*90 (<1) 34140*88 give 44105*08, 45882*98. 
^^ + ( 2 ) 39969*62 = 44102*8 with the v^, 1/3 lines in the ultra-violet, but an extra 
V sounder gives u + v + {C) 37320*68 813*93 (l) 38134*61 = 45881*86, 46695*79, 
the former being 1779*06 ahead of 44102*80. 
m = 4. e + (l) 39292*42 1784*28 (1) 41076*70 = 46606*52, 48390*80 with 
2e + {4) 34569*89 = 49198*09 which is 1777*90 + 813*67 above 40606. 
m = 5. 2e + {2u) 33332*22 1779*90 + 813*68 (2) 35923*80 = 47960*42, 50552*00 ; 
also e + 'M + (l) 38292*32 815*34 (1) 39107*56 = 49739*60, 50554*94; the former 
being 1777*79 above the calculated first line of 47961*81. 
The Value 0/ the Xenon Oun .—In the case of xenon the triplet disturbance appears 
to be small. The result has been obtained that Aj = 24893 = 40f(^ and A 3 = 10999 
= 18(5, giving respectively for S the values 610*87, 611*05 or 610*94 from Ai +A 3 . In 
the preceding 611 has been adopted for S which is sufficiently close except where 
very large multiples of S are in question. To obtain more accurate values of A 2 
recourse must be had to the F and D sequences. Incidentally they have already been 
touched upon, hut we are now in a position by a discussion of the whole material to 
attain a greater exactness. 
Xenon, as has been seen, shows numbers of parallel displaced groups of D and F 
series, each of which gives data for the determination of Ag. Unfortunately those 
lines which might he expected to give the most accurate values are in the ultra-red 
beyond the observed region, and the process of extrapolation by the i/j separation, or 
by links, leaves a considerable margin of uncertainty owing to the 1780 modification 
