438 
DR. W. M. HICKS : A CRITICAL STUDY OF SPECTRAL SERIES. 
Si ( 2 ) should be a strong line in the neighbourhood of 25900, with 82 ( 2 ), 83 ( 2 ) in 
the ultra-violet. There are three strong lines in this region, viz. (8) 2526273, 
( 10 ) 25769’9, ( 10 ) 26633‘64. The last is that which has been seen to be a parallel to 
Si ( 1 ). The first line gives a mantissa less than that for Si (l), and therefore would 
make the a constant positive, in opposition to all experience for S series. We are 
left therefore with 25769’9±3, but this is a C.E,. copper line and so far dubious. If, 
however, it be taken as Si (2) the formula for the S series is 
n = 50403-N 
m+-129855 
•039596? 
m 
The value of Si (3) calculated from this is 39112'08. Sounding with —v gives 
25432'08. Watson gives a line at (o) 25432'3±1 and this is corroborative so far as 
it goes, but the formula is out of step with those for A, Kr, X, and does not give 
confidence. If, however, lower intensities are admitted it is possible to obtain lines 
which fall in excellently with all the conditions, and moreover indicate other displaced 
sets. We find the lines, to which extrapolated lines are added 
(3) 25416-89 (R) [30788-59] (O) 25432-35 (W.) i^i [30803-05] 
(2) 25425-51 (W.) [30796-21] (O) 25457-0 (W.) vi [308277] 
(1) 25453-1 (R.) 
If the extrapolated lines are sounded for by —v, the 30803-05 should give a 
line at 17123-05. This was seen by W. at (O) 17123-0, the nearest to this being 
( 1 ) 17150-93 (R.) which might possibly be within error limits of u.[30827-7]. If, 
with this indication of 25432-35, 30803-0 as part of a triplet set suitable for S (2) we 
calculate the formula with the previously alloted Sj (1) and S ( 00 ), it comes to 
x = 50403-Ny^|w-h-101230- 
which is m close analogy with that for the other elements. For m = 3 it gives 
38972-54. A u-sounder requires a line at 25292-54. Royds has observed (3) 25292-12, 
and again in this neighbourhood we find some close lines observed by only one of W. 
or R., viz., (8) 25262-73 (W. and R.),'* (2) 25299-1 (W.) again evidencing the 
presence of displacements. For m — 2> the oun produces a change in the sequent 
of 3 - 30 , so that 25299-1 which is 6-66 above S^ (3) is Sj (3) (2(^i) exactly, and 25262-73 
which is 29-39 behind is Sj (3) ( —9(^i). The lines calculated from the formula for 
m — 3 ... 8 are given in the accompanying list, which also gives the values as sounded 
* R. gives intensity 8, W. gives 3, although as a rule W.’s intensities are higher than R.’s—again 
pointing to changed displacements with changed conditions of excitation. 
