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



;:,,.,,. ivsiilts ;is holding, rccaJflBklia l ; i the deaOfeiltttON ;ni<l dismiss (In- 

 ment now required. It may be noted, however, that in the Zn sub-group a factor 

 (1 +xitY in D, ( oo ) would reduce the calculated oun below 362'4w* and (l -y<\) 3 raise; 

 it in the Ca sub-group above 361'GOw 8 and at the same time increase the factors in 

 the numbers above towards (l+6J,)'and (l +<?,)'. The factors may of course enter 

 -it her as (l+x$Y or (l- 



Collaterals. 



The first set in doublet or triplet S or P series is always the stronger. The others 

 may l>e considered as receiving a sort of lateral displacement, by the atomic weight 

 term, in the recognised way, and may be called collaterals. This kind of displacement 

 is, however, not confined to the series generally recognised, but is of very common 

 occurrence, and, indeed, depends not only on the A but also on other multiples of S. 

 In fact, the doublet and triplet series are only special cases of a law of very wide 

 application. Some evidence of its existence will be given below. It will be sufficient 

 now only to refer to certain points connected with the law, and to a convenient 

 notation to represent it. This kind of relation was first noted in the spectra of the 

 alkaline earths,* and as the lines are both numerous and at the same time strong and 

 well defined, and, therefore, with very small observation errors, any arguments based 

 on them must have special weight. Moreover, there are long series of step by step 

 displacements involving large multiples of A between initial and final lines, so that 

 we may feel some certainty that these large multiples are real and not mere 

 coincidences. 



As a compact notation is desirable the following has been adopted. In general t 

 the wave number of a line is determined by a formula of the form N/D^-N/D,,, 2 , and 

 lateral displacements may be produced by the addition (or subtraction) of multiples 

 of S, say xS or xA, to D, or D m . This is indicated by writing (xS) to the left of the 

 symbol of the original line when it is added to D,, and to the right when added to D m . 

 Thus CaS 1 (2) is 6162'46. So far as numerical agreement goes G439'36 is a collateral 

 of this represented by (2A, + 10A 2 ) CaS, (2) ( + A 2 ). This means that whereas, see [II.], 



Wave number of CaS, (2) = 7 -^- J*_ 



(1796470) 2 (2-4S4994) 2 



Wave number of 6439'36 = -, - _ __ ^ _ , 



(1796470 + 2A. + 10A,) 2 (2'484994 + A a ) 2 



N N 



(1-815732) 2 (2'48G362) 2< 



A note on this relationship was given at the Portsmouth meeting of the British Association, see 

 'Report, B. A.' (1911), p. 342. 



t Though not always, as I hope to show in a future communication. 





