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



possible from any preconceived theories as to the origin of the vibrations which give 

 the lines. The aim has been to discover relations, which it must be the object of 

 theories to explain. Nevertheless, the way in which multiples of a quantity depending 

 directly on the element enter, and indeed multiples of these multiples, irresistibly 

 suggests that each line is due to a special configuration built up of aggregates of the 

 same kind. Thus, in the Zn group appear multiples of 6^, in Mg, of 5(5,, &c. These 

 smaller aggregates peculiar to a group then appear to enter like radicals into more 

 complex aggregates, e.g., in Zn Aj = 31<V A 2 = 15^ B , and again, multiples of A 2 occur 

 in collaterals. In cases, a certain aggregate, normally to be expected, appears to be 

 affected with instability, a certain number of ouns are expelled or added and we get 

 a stable collateral. In the case of rich spectra and of spark spectra, a very large 

 proportion of the lines appear to be collaterally connected. It suggests systems in 

 which a greater freedom of aggregation is permissible. But there is another way in 

 which the matter may be looked at. The actual multiples may be determined by the 

 number of electrons taking part in the vibrations, and the quantity enters into the 

 formula as the product of this number by a fundamental quantity of the atom. But 

 it is difficult to see how this quantity should depend on the square of the mass. It 

 would almost look as if the gravitational pressure of two atoms always at the same 

 distance produced some change in the configuration of the surrounding aether 

 proportional to the pressure, and that the vibrations were conditioned by this change 

 and by definite numbers of electrons. In any case, the existence of the oun, and the 

 extent in which its influence is shown in a spectrum, point to the conclusion that the 

 positive atom plays an essential part in at least those vibrations emitted which are 

 slow enough for us to observe. 



APPENDIX I. 



The Value of A in Scandium. 



The value of A as a multiple of $ in Scandium is of importance in connection with 

 the evidence as to the curious relation, that the A's of the first elements of the two 

 sub-groups in the n th group are multiples of (2n+l) ^ and (2n + 2) S^ The lines in 

 the visible part have been measured by FOWLER,* and lines both in visible and ultra- 

 violet by EXNER and HASHEK.f 



I do not altogether feel full confidence in the allocation suggested below, but it 

 gives related series, even if not the typical ones, and so will serve to determine A. 

 The doublet separation is 320+ a small fraction. There are over 34 doublets with 

 this separation two, 3613'96, 357271 and 3576'52, 3535'88 containing some of the 

 strongest lines in the spectrum. The lines suggested for the S series appear to show 



* ' Phil. Trans.,' 209, p. 66. 



t ' Spektren der Elemente : Bogenspektren.' 



