DE. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 341 



corresponding observed satellite separations. It also accounts for the appearance of 

 F satellites as shown here and in [III., pp. 389-395] in connection with the F lines 

 in the alkaline earths. The matter is considered in detail for Kr (p. 363) and is found 

 to hold for the cases of the other rare gases. 



The Atomic Weight. It is clear that an accurate knowledge of a first f sequent, 

 or of a d sequent which belongs to the satellite involving the A 2 multiple, 

 gives the means of determining the oun to in general a unit in the sixth significant 

 figure. For these mantissse are usually of the order of magnitude of 0'8 and are 

 known to six figures. Hence, if the multiple is known, A 2 can itself be determined, 

 and since A 2 is a known multiple of the oun (determined by the S multiplet 

 separations), the oun is also known to the same degree of accuracy. Further, as the 

 sources of determining it are often quite independent they serve as tests of the 

 determinativeness of the oun itself to the same degree of accuracy. When A a is 

 considerable, its value is known sufficiently well for it to determine the multiple, 

 and then this exact integer conversely gives the exact value of A.,. In the cases of 

 A and Ne, however, the values of A 2 are too small to determine uniquely this multiple 

 directly. The difficulty, however, is surmounted by obtaining successively values 

 with increasing accuracy from other considerations until the final test can be applied. 

 As a fact the Ne oun is amongst the most accurate found. Its determination (p. 40 1) 

 is specially interesting, and indeed is only possible because the material at disposal 

 depends on interferential measures and large accurately known separations. That 

 of X also is a good determination, and is interesting as depending on a number of 

 quite independent data. 



As the oun is proportional to the square of the atomic weight within the limits of 

 error of determination of the latter, it is natural to assume that the relation is exact 

 and that S = q.w 1 , where q is a number between 3Gl'8'l. If this were sustained it 

 would be possible to obtain w with twice the degree of accuracy of the oun and 

 therefore far in advance of any obtainable by chemical methods. In fact the question 

 is raised as to what is actually understood by the atomic weight. Does it refer to 

 the mass of the positive nucleus, or to that and all or a portion of the electrons ? 

 The hope might even be entertained of obtaining by this method some knowledge of 

 the number of electrons partaking in the emission of a line if slight changes in the 

 oun could be found. For instance, we shall find in these spectra not a single group 

 of S, D, or F series as in arc spectra, but several independent groups, viz. , d and f 

 sequents, depending on different multiples of A 2 . If these gave slightly different 

 values of the oun it could be explained by a transference of electrons. There is little 

 evidence of such variation, but it might occur, for instance, in the oun as deduced 

 respectively from A : and A 3 . As A : depends alone on the measurement of the ^ 

 separation of a triplet it is not susceptible of such exact determination as A 2 , and, as 

 a fact, a suspicion sometimes arises that such a slight difference may exist, and that 

 S from /! is somewhat less than from v 2 [III., p. 333] as also here. 



