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



It is a remarkable fact also, and one which will probably be of importance in 

 throwing light on molecular constitution, that all those elements which do not 

 exhibit satellites have order differences depending on multiples of A, whereas all the 

 others (Al excepted) depend on multiples of the oun, S or <\. The elements without 

 satellites are Na, K, Mg, possibly Al, both series of O, and S. All these depend on 

 multiples of A 2 or A t . None of the others do so, and it may be regarded as an 

 argument in favour of Kb possessing satellite series that its differences do not depend 

 on A directly. It would appear that Rb only begins to show them for m 3. For 

 m = 2 the line is not split up into a chief line and satellite, the doublet separation is 

 normal, and it is instructive to observe that the order separation between the first 

 set and second line is close to 5 A, and only deviates from it in the same way that is 

 mentioned in the previous paragraph. Also Ba seems to have in the same way no 

 satellite for m = 2, the separation is quite normal, and this also shows a first order 

 difference very close to Aj.* But Ca, on the contrary, which has a first difference 

 = 99A 2 , possesses satellites. 



It is noticeable also that the high atomic weight elements appear to follow more 

 regular and simple rules. Thus both Cs and Tl show descent by equal steps in both 

 cases = 3<^. 



The result of the discussion would seem to be that there can be no doubt but 

 that satellite differences as well as the doublet and triplet differences depend on 

 multiples of the oun. For the other supposition, viz., that in the Diffuse series the 

 order differences also depend on differences of the oun, it can only be said that a case 

 has been made out. The supposition in all cases fits conditions, but the conditions 

 are not all sufficiently definite to give certainty. After the first two or three orders 

 the observation errors are larger than the S lt and even for these the value of S l for 

 the low atomic weights is comparable with the errors. In some of these cases, 

 however, multiples of A which is much larger enter and strengthen the argument. 

 The strongest examples are those of the alkaline earths (small errors and large A or 

 Sj}, first lines of Cd, and Hg, Al (series in A), In, Tl, and the A series of O and S. 



The D (2) Term. If the foregoing theory of the constitution of the Diffuse series 

 is correct, it is further necessary, in order to complete the discussion, to determine 

 the origin of the first term. The apparently close relation of the F series to the D 

 series, and the several cases of collaterals of the former which had been noted with 

 large multiples of A, suggested a trial to see if the denominators were multiples of 

 this quantity. As in cases where satellites are present, the separations depend on 

 them and not on the strong line, it is natural to expect that the satellite is a normal 

 line and the strong line a collateral, and this is found to be justified by the calcu- 

 lations on this theory. In Table III. the first column of figures gives the value of 

 the denominator taken from Table II. The second column gives the factors together 

 with possible variations. Thus the denominator of KD U (2) = '853302. This has 



* But see discussion of BaF below. 





