344 
DE. 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 Sg, and consequently different A'g, Ag, they 
give the same oim, and in connection with them appear two D groups whose outside 
satellites depend one on a multiple of A '2 a^nd the other on a multiple of A 2 . It is to 
l 3 e 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(l) triplet was found. XS, AS come next in order of definiteness. The 
spectra of RaEin 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 KaEm, the D and F for A, and, lastly, 
the whole sets for Ne. Led by possibly a false analogy to He [L, 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 in 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 
as 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 
l)eyond 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 billing 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 l)een 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 tlian 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 Dewar, although the latter are only given to 
