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DR. W. M. HICKS : A CRITICAL STUDY OF SPECTRAL SERIES. 
Radium emanation. 
„ analogue of 1864 in XE. . 
,, general considerations for S.D, 
,, value of S ( oo) and e link . , 
„ ,, P ( 00 ) and a.?; links . 
,, S series. 
„ D series. 
,, source of 5648 separations . , 
„ value of the oun .... 
Argon, D series. 
,, (- 56) D series. 
„ E and F series. 
„ value of the oun. 
„ Analogue of 1864 XF. . . . 
Neon... 
,, F series . -. 
,, parallel F sets. 
,, F series. 
„ S „. 
,, e link. 
,, normal D and S lines 
„ value of the oun . 
,, Watson’s separations 
„ Rossi’s series . . . 
Table of constants . . . 
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The present communication has two objects. Its subject matter is an attempt to 
obtain some knowledge of the series relations in the spectra of the group of the 
monatomic rare gases Ne to RaEm, whilst the methods employed will serve to 
illustrate the fundamental importance as instruments for further research of the new 
facts brought to light in the previous communications.* The importance of the first 
object will be generally acknowledged, but it does not yet seem to be realised how 
definite and exact those new relationships are, even in their as yet undeveloped form, 
and how powerful an instrument is placed in our hands for the analysis of spectra. 
It may be well therefore to commence by a brief resume of some of these laws as 
apphed in the succeeding pages. Further, as the establishment of the results 
obtained must by its nature depend on the numerical comparison of a very large 
number of lines in all five spectra, and as this evidence must be fully set out to 
* “ A Critical Study of Spectral Series,” Part I., ‘ Phil. Trans.,’ A, vol. 210, p. 57. 
„ „ „ Part 11. „ „ 212, p. 33. 
,, ,, ,, Part HI. ,, ,, 213, p. 323. 
„ „ „ Part IV. „ „ 217, p. 361. 
These will be referred to respectively as [L], [IL], [HI.], [IVd- 
