DR. W. M. HICKS: A CRITICAL STUDY OP SPECTRAL SERIES 345 



the nearest Angstrom. The most complete and reliable sets of measurements are by 

 BALY* (red spectrum 64563502 ; blue 58712418), and Lswist (blue 24162145), 

 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 Sj or Dj line is followed by a line with a separation very close to J^. 

 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 

 S 3 series, one with v 2 = 309 and the other with i/ 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 A 2 , 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). 

 J 'C.R.,' March 25 (1913). 

 'Kong. Fys. Sails. Hand.,' N.F. 25, Nr. 12. 



3 B 2 



