DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES 
345 
the nearest Angstrom. The most complete and reliable sets of measurements are by 
Baly* * * § (red spectrum 6456—3502 ; blue 5871—2418), and Lewis! (blue 2416—2145), 
both of about the same degree of accuracy with probable error in the neighbourhood 
of '03 A. Of exact measures there are only two by Fabry and BuissonJ for lines 
at 5870.9172, 5570.2908 LA. In the red spectrum Kunge has pointed out constant 
separations of 945, to which Paulson § has added three others. The observations of 
Lewis gave me the first clue to the KrS set of lines and thus formed the starting 
point for the present communication, although a great deal of preliminary discussion 
of material for this group of elements had been previously done, especially in 
connection with the separations for certain linkages. In the case of Kr a very 
large number of separations in the neighbourhood of 786 to 788 had been found, 
connected also with others of 309, indicating groups of triplets having these values 
for V. 2 . Amongst Lewis’ lines a set was found with separations in the reverse 
order, clearly pointing to a first set of — S (l) or +P (l) lines and corresponding sets 
for other orders were then easily found. It would seem that there are always a 
considerable number of separations governed by oun displacements in the limits of the 
first order, and that of these, three seem to be of a more stable value and correspond 
to normal triplets. For instance, in all these gases, we find a very large number of 
cases where a or Di line is followed by a fine with a separation very close to 
They force themselves on attention on account of their value being so close to the 
half of a number being sought for, and others may be present although they have 
not been looked for. In the present case two alternative sets of lines for the 
Sg series, one with i/g = 309 and the other with V 2 — 341 appear. In the original 
search the former was taken because it is reproduced in the D series as well. But 
later certain difficulties in the determination of the oun, combined with the fact that 
the corresponding oun multiple in Ag, although quite definite, is out of step with the 
march of their values in the other gases, led me to include the second. This gives 
a multiple quite in step with the others, and also affords the means of obtaining 
a good approximation to the oun. 
The lines are given in the following table, which also embrace a few obtained by 
sounding, both wave-lengths and wave-numbers are given :— 
* ‘Trans. Roy. Soc.,’ A, vol. 202, p. 183 (1903). 
t ‘Astro. Journ.,’ 43, p. 67 (1915). 
t ‘C.R.,’March 25 (1913). 
§ ‘ Kong. Fys. Sails. Hand.,’ N.F. 25, Nr. 12. 
3 B 2 
