DR. W. M. HICKS : A CRITICAL STUDY OF SPECTRAL SERIES. 
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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 firsty sequent, 
or of a d sequent which belongs to the satellite involving the A, 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. As can itself be determined, 
and since Ag 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 Ag is 
considerable, its value is known sufiiciently well for it to determine the multiple, 
and then this exact integer conversely gives the exact value of Ag. In the cases of 
A and Ne, however, the values of Ag 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. 461) 
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 ^ = q.iv^, where g is a number between 361'8±T. If this were sustained it 
would be possible to obtain iv 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 Ag. 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 Aj. As Ai depends alone on the measurement of the 
separation of a triplet it is not susceptible of such exact determination as As, and, as 
a fact, a suspicion sometimes arises that such a slight difference may exist, and that 
(5 from vi is somewhat less than from j/g [HI., p. 333] as also here. 
