340 DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



in [IV.] that the e link appeared to have a tendency to increase the intensity of one 

 of the two lines to which it was attached. The method may be illustrated by an 

 example from KrS. In Kr, e = 3183'35. The value of S, (5) as calculated from the 

 formula is 474 19 '39, which is in the ultra-violet outside the observed region. But 

 47419'39 e = 44236'04. This is within the observed region, and as a fact the 

 corresponding line is found at 44237 '61 with d\ = '08 if e is free from error. As 

 an individual case this might be due to a coincidence, but when the same effect occurs 

 with line after line the cumulative effect becomes convincing. To see this it is 

 necessary to get at a glance a survey of all the cases, and for this purpose they are 

 exhibited in sets of diagrams in Plate 3. These diagrams also include links within 

 the observed region in order to show that where the method can be tested it holds. 

 It may be specially noted how the similar arrangement of sounders holds for the same 

 order in the three lines of the same triplet, and how in certain cases the u, v seem 

 alternative. Cf. for example XS (l, 3, 4, 7, 8), or the main lines of the three parallel 

 D sets in X, viz. (2S i )D n , D u , ( 2^)0,,, or particularly the prevalence of the 

 (e+v) combinations in the unobserved lines for KrD. In RaEm these links are 

 too large to be of wide application and in Ne too small to be of use. In RaEm 

 the e link is .23678 and can reach from the unobserved ultra-red across to the 

 unobserved ultra-violet. In Ne the e link is 196, so that its reach is too small to be 

 useful. As'this method of sounding is new and clearly of importance if substantiated, 

 considerable attention has been given to its illustration, but as the details themselves 

 are only necessary for a critical study they have been printed in smaller type and 

 may be omitted on a first reading. 



Abnormal D triplet Separations. It has generally been held since RYDBERG'S 

 discovery of the satellite systems that the triplet separations for the D and S series 

 are the same. The actual measures did not absolutely prove this, in fact, they 

 indicated small differences, but the accuracy was not sufficient to establish a real 

 difference especially as against a natural bias to expect equality. MEGGERS,* however, 

 has recently placed it beyond doubt that frequently the separations are really 

 different. In Group I., for instance, the separations as measured from D lines are 

 less than those determined from S lines. In the rare gases also this difference appears 

 quite decisively, but here (group 0) the separations as determined from the D lines 

 are, in general, larger than those from S. The key to the explanation is found in the 

 fact that the difference between the two determinations diminishes with increasing 

 order in other words, that the sequent in the same set of satellites is not the same, 

 and that in a large number of cases the value of i/j + v a is the same in both S and D 

 although i>!, v 2 themselves are different. It is found to be completely explained by 

 the displacement of one or two ouns between the sequents of the first or second 

 members of a triplet. Sometimes it occurs in the third member. The same explana- 

 tion accounts for the fact that the F separations are frequently smaller than the 



* 'Bur. Stand.,' Washington, No. 312 (1918). 



