DE. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 373 



The numerical agreement is very close, and 19956 is a series inequality in which a 

 change of 1 makes the two separations 822, 308 exact d and c 6 links. On the other 

 hand, as we have already pointed out, 20991 may be a D n line depending on the 

 limit (7J,)D(oo). 



The following points should be noticed in the foregoing allocations : 



(1) The presence of the large displacements in the sequence term by quantities 

 differing from multiples of A 2 by one or two ouns in this respect quite analogous to a 

 corresponding effect in the alkaline earths. It seems to point to a kind of satellite 

 effect in the F series analogous to that shown in the D 1; where the main strong line is 

 displaced from the normal satellite depending on a multiple of A 2 by the addition 

 of a few ouns. In this case the F satellite is in general too weak to be observed, 

 except possibly the linked line 22203 = X 7 (-2^) . e depending on/ (2) ( 17AV). 



(2) That where a multiplet line is absent, it frequently appears as a linked e line, 

 but that the linked line never appears directly linked to the FI. 



(3) The line 20991 occurs twice as F 6 (7A' a ). and as F 8 (51A' a ), also its possible 

 existence as a kind of independent D H line has already been referred to. It cannot of 

 course be all, and at least two of the suppositions must be due to chance. It is also 

 probable that such coincidences may occur in some of the other allocations. The 

 evidence for the general effect is cumulative and not dependent on a single numerical 

 agreement. 



The F system of the first order (m = 2) have been considered in rather considerable 

 detail in order to establish what appears to be a very general rule that in many 

 groups of elements the configurations producing the normal F lines appear to have 

 been subjected to a sort of explosive effect whereby other configurations producing 

 f sequents displaced by large multiples of A 2 are produced. As a natural result the 

 intensities of the normal lines in the spectrum are diminished since the observed 

 intensities must depend on the number of emitting centres as well as the energy 

 emitted by each. We have seen that they are displaced in pairs or sets containing 

 one displaced F t line, but no attempt has been made to search for sets not containing 

 the Fj. As we shall see later these displaced sets in the lowest order give a means of 

 obtaining very accurate data for the determination of the value of the oun. In 

 dealing with subsequent orders such a detailed discussion is not called for for this 

 purpose. 



m = 3. The normal lines are observed for F,, F 6 , F 8 , and as illustrating the 

 correctness of the explanation given above for the diminished separation 301 in place 

 of 307 it will be noticed that the normal D value is shown by the line 23349. The 

 other F lines of the set do not directly appear, but as in the case of m = 2, they are in 

 evidence as linked lines. Some of the lines linked to F, (3), are represented in a map 

 in Plate 5. The denotations of the lines are entered in place of the wave-numbers, which 

 can be reproduced by adding the given separations, and each can be referred to by 

 the column and order in the column in which it occurs. Again we have several 



