DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
373 
The numerical agreement is very close, and 1995G is a series inequality in which a 
change of 1 makes the two separations 822, 308. exact d and links. On the other 
hand, as we have already pointed out, 20991 may be a line depending on the 
limit (7(5i) D ( 00). 
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 Aa 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^, where the main strong line is 
displaced from the normal satellite depending on a multiple of A^ 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 = Xj ( —2(ij). e depending on/(2) (l7A'2). 
(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 Fj. 
(3) The line 20991 occurs twice as F5(7A'2).e and as F8(51A'2), also its possible 
existence as a kind of independent 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 
acfreement. 
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 Aa 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^ 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], Fg, Fg, 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 Fj (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 
