344 DK. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



sets of lines suitable for S 3 in other words, there are quadruplets. Whilst the two 

 sets S' 3 , S 3 give different separations with S 2 , and consequently different A' 2 , A 2 , they 

 give 'the same oun, and in connection with them appear two D groups whose outside 

 satellites depend one on a multiple of A' 2 and the other on a multiple of A 2 . It is to 

 be suspected that this is only one example of what may be a common occurrence in 

 spark spectra. 



The order of presentation is generally that in which the investigation was taken. 

 The key was found in obtaining the KrS system, a result first rendered possible by 

 the publication of wave-lengths in the ultra-violet by LEWIS (1915). Amongst them 

 the KrS ( 1 ) triplet was found. XS, AS come next in order of definiteness. The 

 spectra of RaEm and Ne are more difficult to deal with, the first because of its 

 defectiveness in range, number of lines, and accuracy, and the latter because of the 

 smallness of its oun and its triplet separations. After the S series of Kr, X, A come 

 the D and F series of Kr, X, the spectrum of RaEm, the D and F for A, and, lastly, 

 the whole sets for Ne. Led by possibly a false analogy to He [I., p. 105], in which 

 doublet series appear in the blue spectrum, the blue spectra were chosen for investi- 

 gation, and the family group being of even order triplets were looked for. In Ne, 

 with a single spectrum of composite character, the results obtained may have some 

 reference to the red type as well as the blue, especially iu connection with certain 

 remarkable constant separations found by WATSON and analogous to the RYDBERG 

 constant separations in the red spectrum of A. One is inclined to think that these 

 red spectra consist mainly of lines of the F type. But the red or first spectra are 

 outside the scope of the present communication. Although it is a very lengthy one 

 us it stands only the beginning of an analysis has been made. The aim has been to 

 lay the foundation for the series framework of this family of elements, and little 

 beyond has been done. The linkages, as a whole, have not been isolated, the red 

 spectra not touched upon, and many interesting effects which will require clearing up 

 are passed over without reference. A great field for investigation is open in these 

 and other spectra for any who are willing to give the necessary time and patience. 

 In some few cases the presentation might have been slightly shortened by merely 

 stating the final result and showing how the necessary conditions are satisfied. But 

 not only would this have passed over certain phenomena of special interest, but 

 one of the objects of the present communication would have been missed, viz., to 

 illustrate the power of the new facts to guide a search even when the details 

 are most bewildering. Moreover, the evidence itself is the more striking when 

 developed from step to step than when the result is directly presented as a finished 

 product. 



Krypton. Krypton shows two spectra, without and with capacity, the 'former in 

 the red region and the latter further towards the blue. We have measures of some 

 of the stronger lines by RUNGE, and a considerable number of weaker lines, not 

 observed by others, by LIVEING and DEWAK, although the latter are only given to 



