DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
55 
2'907231 would make the first number '6659, and, therefore, quite out of analojry 
witli the others. Again, in the alkalies the same law is seen, witli just the same 
modification as in the previous case, viz., constant for each. 
A closer inspection shows that the differences between the P terms cannot he 
exactly constant after m = 2. They seem to descend in two steps instead of one. 
The general law, however, seems so well established that the cause of the real 
variation is to be sought. It is possible it may be due to the properties of the atomic 
weight term. The second law, however, affecting S, P seems to be very closely 
followed. It should he noticed that the alkalies and A1 give differences less than '5, 
whereas the others give values greater than ’5. It suggests that the remainder of 
the A1 sub-group, viz.. Sc, Y, La, Yb, would also require values less than '5. If such 
a rule held for the two sub-groups in each group of the periodic table, we sliould 
expect the Mg, Ca, &c., to require values less than '5. The evidence, however (see 
below), is rather against this so far as any evidence is available. 
In the alkalies the Principal series are formed on the p-sequence, and the 
subtraction of the respective constants by the second of the above laws gives the 
first term of the S series as hitherto recognised. The question naturally arises, what 
becomes of the term deduced in a similar way from the first term of the s-sequence, 
and do lines exist corresponding to these ? If we attempt to calculate them we must 
know the value of the constant to be deducted. Is it the same as for m = 2, which 
is larger than that for the others, or is it a number larger still ? If we use the rough 
values obtained for ni = 2 in Table III. and apply them to m = 1, the following 
values of the denominator result:— 
Zn . . 1'0710; Cd . . I'llfO; Hg . . 1'0494 ; A1 . . 1'0203; T1 . . 1'0313; 
corresponding to lines in the neighbourhood of 
Zn. 
Cd. 
Hg. 
Al. 
Tl. 
'.3 • 
. 191(3 
2198 
1884 
'2 • 
. 1909 
2173 
1824 
1752 
1856 
1 • 
. 1896 
2119 
1682 
1748 
1622 
We should expect such lines, if they exist, to be exceptionally strong. A number 
of weak lines are known in these regions, but the only strong ones that could possibly 
belong are the Cd lines— 
Intensity. 
A, 
n. 
1 . . . 
. 2170'11 
46066'38 +10’6 
551 - 26±14 
4,r. 
. 2144'45 
46617'64± 4'3 
1076*36 ±15 
3w. . . 
. 2096'! 
47694-00+11 
