DR W. M.' HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 331 



the values of A, + A 3 come much closer to it. The values of (A, + A;,)/t^ are therefore 

 added to the table. It is clear, however, that when the spectroscopic observations 

 are good, the relation here established will enable very accurate measures of the 

 atomic weight to be obtained. In fact, with the possible accuracy attainable in 

 spectroscopic measurements, it may be hoped to obtain far more reliable values of these 

 constants than by weighing, except in those cases where they are small. The table, 

 for example, affords considerable support for BRAUNER'S estimates, except, possibly, 

 in the Mg group, where the irregularities are due to spectral causes. The case of Zn 

 may be taken as an example here. Its spectral values are very good, it shows with 

 w = 65'40 the multiple 543'357 instead of 542'70'30. If the excess is due to the 

 value of the atomic weight, it should be '048 larger, which would be allowable within 

 BRAUNER'S estimates to bring it to the adopted value of q, i.e., w = 65*448. This is 

 more fully considered below. The numbers for Se also seem to show that 79'2 is too 

 small for its atomic weight. 79'40 would make q for A, = 362'16 and for A a = 36177, 

 and the spectral uncertainties would account for the outstanding differences. 



If $i is written for ^3, it may be noticed that the values of the A for the first of 

 each sub-group may be written 



i. ii. iii. vi. 



Na. Cu. Mg.* Zn. Sc. Al. S. 



1553, 50 x43, 32x53, 31x63, 52x73, 33x83, 8x143, 



and, moreover, the same multiples of 3, recur in several of the same group, e.g., 

 A, + A 2 for Zn, Cd, and Hg, and A, for Eu are all multiples of 63,, also the 53, occurs 

 in Mg, Sr, Ba, and Ra. Analogy would lead to a corresponding 33, for Na. The 

 values of the atomic weight and the doublet separations of Na are known with great 

 accuracy, and no possible value given to could change the multiple from 155 to 156 

 or 153. The only loophole for an explanation may be that the value of v as found by 

 FABRY and PEROT comes from the Principal series, and that VP,(l) is not really 

 S(oo). This latter point has been discussed in [I.] and also in [II., p. 38]. It is 

 equivalent to a considerable change in S ( o ). To obtain a value 156 or 52 x 3 would 

 require an increase of '07 in v, i.e., to 17 '25, Such a value would be quite well in 

 consonance with the measures of SAUNDERS and of K. and R. for other doublets, e.g., 

 D(2) 17'30 (S.), S(3) 17'22'26 (K.R), S(4) 17'05'38 (K.R.), P(l) 17'20 (K.R.). 

 But FABRY and PEROT'S values for P(l) independently verified by Lord RAYLEIGH 

 would seem conclusive against this value, unless F. and P.'s apply only to VP (l) 

 and 17'25 to S ( ). This would correspond to a lateral displacement of 3, (see below) 

 between VP (l) and S ( oo ). 



S and Se both give 8 x 143, which falls in line with the other sub-groups. In fact, 



1 This is the value first deduced when the international system of atomic weights was used. It is 

 '^i more than that in the table. The question is considered below. 



2 T7 2 



