410 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
he 30740‘21+2031270 = 51052'91 which is 27'62 above the normal and has no 
reference to the onn displacement. If 2031270 corresponds to the — tdj indicated, 
the limit is 5106779 and the d sequent is the difference, or 30755'09. This is the 
source of the 1864 separations. It is 2279 greater than the limit 30725'30 of the 
F series considered in connection with this series and which gave 1864’10 and 829‘64. 
This limit corresponds to a sequent 6^i less displacement or 29‘82 greater value which 
is practically exact. This present sequent will therefore increase 1864'10 hy 6x '45 to 
186670 and 829’64 hy 6 x'22 to 830'96. The new sum is 2697'66, as against the 
observed 2697‘44 in remarkably close agreement. This then supports the — 4(5i 
indication of the capability test. A — 3(5i displacement would make the sum = 2697’00 
—which though a worse agreement may yet be within observation errors. The same 
— 3(^1 would make the modified = 1779'50 + 4'97 = 1784'47, or 72 greater than the - 
observed. One is almost tempted to suspect here an error greater than the ordinary 
ol)servation error. An error of '36, d\ = — ‘09, would make all three tests agree in 
allotting 20312 to the — 3(ii set, and would bring it into the group of lines considered 
in Case 1. 
It should be noted that this 20312 line is the line with wave-length 4922 referred 
to by Liyeing and Dewar for its peculiar behaviour {see p. 350). 
( 4 ) The separations of the triplet 19880 are 1778'42, 815'30. They suggest the 
separation —to which belong 1778'43, 815’42. The capability test gives —3(^i and 
the two are incompatible. In the D series given below the calculated limit from 
the first three lines give the limit as 51045'37 or 20‘08 above the normal. With the 
uncertainty in a limit found in this way this is a displacement of —2Si which gives 
21'25. Further there seems some evidence to show that this line with 20021, 20041, 
20312, 20500, 20559 belong to one D (l) group of lijies. The evidence consists in the 
existence of parallel F sets showing displacements equal to the separations of these 
lines. In other words these lines are D sets with the same limit. All these tests 
mutually exclude each other. How can their indications be reconciled ? I suggest 
( 1 ) The limit for the line is {-Si) D ( 00 ) and the observed v^, V 2 are thus explained. 
( 2 ) The capability test is met by the transfer of six electrons indicated above. 
( 3 ) It is not the first line of the series in question. 
( 4 ) The F separations will be found to offer a natural explanation. 
In what has preceded an attempt has been made to allocate normal D series, but 
they are clearly not the strongest sets. In my first attack on the D, F problem the 
procedure adopted was to take the 19880 triplet as a clear satellite set, and attempt 
by the application of Rydberg’s table to find a series for this satellite series. The 
three sets found were ;—■ 
(1)19880 
1778-42 
(5) 21659-14 
815-30 
( 10 ) 22474-44 
[37888-59] 
1777-90 
(1) 39666-49 
814-42 
(2) 40480-91 
[43801-13] 
1777-74 
[45578-87] 
818-18 
[46397-05] 
