82 PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



The numbers do uot suggest the relationship so strongly as those of the preceding 

 cases. The limits, however, are so wide that it is the only one in which the absolute 

 identity of the common factor is possible without overstraining them. 



The values of the a are for all the elements less than for the P series. They are, 

 for the elements in order, 



2['01314(686)], 4 ['011901(346)], 5 ['01257 + (510)-(177)], 6('01200?), 



or easily '0120 within limits of error, but the limits are wide. The ratios of /(/A '5) 

 are '0170, '0140, '0164, '0140. They are not constant, but their irregularity points 

 to a want of law in deviations from equality, or, in other words, that equality exists 

 in the true formulae. There seems something defective in the form for the S series, 

 as has already appeared in its failure to give the first lines S (2), as well as to 

 reproduce the values of P( oo) exactly. 



The Diffuse Series. 



The observations for the D series are not sufficiently exact to enable such certain 

 conclusions to be drawn as in the case of the other two types. Besides, there seems 

 at first sight to be a change of type as we go through the group of elements. 

 Satellites clearly show themselves only in Cs. There is some indication of satellites 

 in Kb, but, as we have already seen, there is considerable doubt as to their actuality. 

 K shows no sign whatever of them. On the contrary, Na does, not by offering 

 satellite lines themselves, but by a regular increase in v as the order increases a 

 point already discussed under the remarks on Table I. The satellite series in general 

 plainly suggest an analogy with the P series, in which the P 2 lines are satellites to 

 the P b and it is natural to search for series whose limits are the VD X (1) and VD 2 (l) 

 giving corresponding doublets. Working on this basis for the clearly defined satellite 

 series of Cs (satellites for Di(3.4.5.6) observed), we get two values for the N/D 2 of 

 the top lines of the formulas determining them which give a separation of 97 '07, and, 

 as we shall see, determine the limits of an additional doublet series. The satellite 

 series are more fully and more numerously developed in other elements than the 

 alkalies, and their general discussion is better deferred until the other elements are 

 discussed in a succeeding communication. 



In determining the value of a the question arises whether p. should be taken to be 

 a fraction or 1 + f. If ^ = f, m = 1 gives a line too far in the ultra red to have been 

 observed. The observations of known lines by themselves are not sufficiently exact 

 to decide the question as, e.g., in the P series. If we regard the doublet separation 

 of an associated series as determined by the top lines of its principal series, then, as 

 we shall see shortly, the evidence in the case of Cs points to the fact that the 

 denominator of the top line = 2 + f, i.e., p = 1 + f ; but there may be some uncertainty 

 here also in view of RYDBERG'S suggestion that each V of a series may form the limit 



