426 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
belong to the modified vy, which D satellites have ali’eady shown in Kr and X, whilst 
5371, 2641 or thereabonts belong to the normal separations depending on displacements 
in the S(co) alone. Moreover, another very frequent separation is 5631, connected 
with other sets as triplets with a v .2 in the neighbourhood of 2800. This at once 
suggests the analogue of the 1864 F series of X. 
A first quite definite starting point, from the material at disposal, is found by a 
search for lines of the F and F type, or the twin A±B sets. The limit A belongs to 
a D sequence, which from analogy with Kr and X should be expected to he of the 
order n = 30000. Now in the observed spectrum there is a long gap between 27671 and 
32031, within which such limit must be. That no lines should be found near this 
limit is to be expected. If, however, such double sets exist we should expect to find 
sets of lines with exactly the same separations on either side of this gap. 
Unfortunately there are only four lines on the violet side, but one such set is found. 
They are 
(1) 26669-23 (0) 33259-05 
897-13 896-91 
(2) 27566-36 (O) 32362-14 
The corresponding limit should be the mean of either of the two corresponding lines, 
viz., 29964-14 or ...4-25, say 29964-20±-05. The possible observed errors in these 
lines are not large and the practically exact equality of the two separations is strong 
evidence of the reality of the suspected connection. But any doubt on this point 
must he removed when it is noted that by Bydberg’s tables, the separation 897 is 
that due to tw'O denominators 5-78, 6-78, whilst if the denominators are calculated 
using 29964 as limit the same values are found. The two residts are quite independezit. 
By a further zise of Bydberg’s tables it is possible to find approximate positions for 
other lines of the F system, the F being quite beyond the observed region in the ultra¬ 
violet. Such lines are found at (5) 15846, (4) 22310-4, (8) 25171 for m = 2, 3, 4. 
Again, connected with 15846, are (3) 21488, (6) 24296-9 giving separations 5642, 2809. 
The lines 22310, 21487 are due to C. B.’s copper electrodes and are subject to considerable 
possible errors d\ = lA, dn =5, or even more. These strikingly correspond to the 
1864 sets in XF. 
The limit 29964-20 must be very accurate and subject only to any systematic errors 
in Pt. and B.’s measurements. This is shown by the exactness of the observed 
separations in sets so far removed from one another as 26669 and 32362. Using this 
limit with the lines 15846, 26669-23 for m = 2 and 5 the calculated formula is 
n = 29964-20-Ny/|m+ -757457 + • 
The two lines used may be regarded as having possible errors dn = 2 and '7 
respectively and any consequent errors in the constants will scarcely affect the 
