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



Unfortunately L.D.'s measures are only given to lA, and thereby their value is 

 greatly diminished as they become merely indicatory and cannot serve as quantitative 

 data. The accuracy of BALY and of WATSON is good and probably about the same. 

 PRIEST claims an accuracy with probable error <'0005A, MEISSNER with error not 

 >'0015, but the accuracy of an interferometer measure depends very largely on 'the 

 nature of the individual line. MEGOERS' results are exceptionally valuable in that he 

 gives interferometer measures of a number of lines of small wave-length 3701 to 3370 

 where the S (2) and some of the higher order F lines occur. Rossi has succeeded in 

 allotting lines to series. 



Neon affords an apparent exception to the rule amongst the rare gases of different 

 spectra, according as they are developed with or without condenser in the tube 

 discharge. On the other hand its spectrum would appear to be a composite one of 

 the typical " red " and " blue " spectra. It undoubtedly has a portion analogous to 

 the " blue " as will be seen by the results obtained below, completely analogous to those 

 found in this communication for the other gases, which refer to their "blue" spectra. 

 On the other hand in some remarkable sets of accurately equal separations discovered 

 by WATSON* it shows a relation to the analogous well-known constant separations 

 observed by RYDBERG in Argon. Further, it is specially rich in lines in the red region. 

 In the list of lines observed at the Bureau of Standards referred to above there are 

 225 between 8783 and 5689. Since in each periodic group of elements the number 

 of lines as a whole increases very rapidly with the atomic weight, the excess of red 

 lines in Ne is even comparatively greater than the actual number shows. The majority 

 of these lines are weak, but they almost all fall into a few definite linkages in which 

 the links are the constant separations discovered by WATSON. Some of these special 

 linkages again are connected together by the p and s links, especially the e.u.v. 

 They belong to the F type of order m = 2, and should afford most valuable 

 information as to the way in which parallel and displaced lines are related. I hope 

 to return to this question on a later occasion, and only refer to them in the present 

 discussion incidentally as they afford some evidence for the determination of the 

 value of the oun. 



The wave-numbers of observed lines published stretch from 13251 to 36536. 

 From analogy with the spectra of the other gases we must not therefore expect to 

 find more than one order in each of the S and D series. Nor, with its small atomic 

 weight will the e.u.v links be large enough to act as efficient sounders. On the other 

 hand the whole of any F series (m = I excepted) should lie within the above limits. 

 It is therefore clear that the attack on the problem must be made first on 

 this series. One datum at least is at our disposal in the magnitude of the oun. 

 Taking the atomic weight at 20'0 '01 the calculated value of is 14'47 '01. 

 This value of 14 '47 may therefore be treated as exact to one or two units in the last 

 digit. 



* ' Proc. Camb. Phil. Soc,,' vol. 16, p. 130 (1911); 'Astro. Journ.,' vol. 33, p. 399 (1911). 



