SS8 



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



greatest weight when derived from the spectra of elements of high atomic weight, or 

 from cases in which the displacements are due to multiples of A. 



It is possible for a line to be simultaneously displaced to right and left, as for 

 instance CaS, (2) given above. Such lines exist, but since there is a very considerable 

 scope for adjustment of values by a proper choice of say x and y in (xS) X (y$), and 

 specially so in y when m > 2, such cases cannot be considered as established unless S is 

 very large, or the A enter only, or unless there is independent evidence by the existence 

 of intermediate steps. 



When these collaterals were first found it was noticed that in general a positive 

 displacement seemed in the majority of cases to increase the intensity of the lines, and 

 a negative to decrease it. This is clear when the displacements considered are those 

 from the 1st to the 2nd set of a doublet series where the displacement is a negative 

 one and there is always a decrease in intensity. It is also evident in the satellites of 

 the D series. Apparently, as will be shown, the typical line of the series is the 

 satellite. The strong line is a positive collateral of this and always shows a great 

 increase of intensity. Although these facts are obvious the connection was not 

 recognised, until the relation showed itself first in a series of collaterals. It is, I think, 

 safe to say that a positive displacement produces a tendency to increase of intensity ; 

 there may be other causes acting so as sometimes to mask the effect, but in general, 

 where the rule appears to be broken, the suggested displacements should be regarded 

 with some doubt. In so far as I have used this rule in the following, the results are 

 biassed and of course the evidence for the rule to that extent weakened. 



It would be possible to give here long lists of collaterals. As, however, the present 

 communication has reference chiefly to the discovery of general laws as a necessary 

 preliminary to the more thorough examination of special spectra, it will be sufficient 

 to refer for evidence to the cases which arise in the succeeding discussion. This seems, 

 however, a natural place to refer to certain cases discussed in Parts I. and II., where 

 unexpected deviations occurred between the calculated and observed position of a line 

 in the middle of a series in which for the other lines the agreement was especially 

 good. As special instances, the cases of TlSj (4) and CaSj (5) [II, p. 39] may be taken. 

 The suggestion that TISj (4) may be due to a transcription error is not valid, and was 

 occasioned by an oversight in confounding d\ with dn. If the normal line be denoted 

 by T1&! (4), the observed is the collateral TlSj (4) (154) giving 0-0= - '01 in place of 

 - 1'21. Similarly, the observed Ca line is CaS! (5) (-6A 2 ) with O-C = - '03 in place 

 of '61. There are many examples of such sudden jumps which are certainly not due 

 to errors of observation. Several instances will be found below in the D series. 



The Diffuse Series. 



To the question what is the positive criterion of a Diffuse series no clear answer up 

 to the present has been given. We find in general three sets of series associated 

 together. Two of these have the same limits, the other a limit peculiar to itself. 



