(56 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
from analogy with Ba and Sr the true value should be expected to be somewhat 
larger than this. It should be noted that it is outside Exxee and Haschek’s region 
of observation ; 21490 may possibly, therefore, he a coiiect identification foi 1)21 ( 0 ). 
The first three lines (m = 3, 4, 5) give the formula 
n = 22760’09-N/{m+fl30149-'1952367?r^}h 
This gives the following values of obs.-cal. of X for the next three (711 = 6, 7, 8), 
viz., -78, -'ll, -’17. The first is too large for an observational error, and the 
true line is possibly hidden by the strong line 4856, but there may possibly he another 
explanation which would at the same time make the others in still better agreement, 
and bring into relation with the series the strong lines 5041'52 (6), 4856’25 (8). As 
this depends on the relations of the atomic-weight terms to D series its discussion 
must be deferred. The object at present is to determine the limit, which cannot be 
far from 22760’09. This should also be the limit for the S series. Using this with 
the two first suggested lines=^ for Si, i.e., (14728‘20) and 1784678, the resulting 
formula for Si is 
n = 22760-00-N/{7n-hl783424-T7628677i-'}l 
The separations i^i = 2050'27, 10 = 832‘00 now give Ai = '092658 and A 2 = '034390, 
but there is some doubt about 1 / 3 . With this value of Ao the denominator of the 
formula may be written 
777-i-l-A2-f'816780 (1-'21582771-'), 
in very close analogy with the other cases. 
APPENDIX II. 
The S and P Series Lines of the 2nd and 3rd Groups of the Periodic Table. 
Mg. 
Ca. 
Si. 
S 2 . 
S 3 . 
Si. 
S 2 . 
S 3 . 
(2) 5183-84 
3336-83 
2942-21 
2781-53 
2698-44 
2649-30 
5172-87 
3332-28 
2938-67 
2778-36 
2695-53 
2646-61 
5167 -.55 
3330-08 
2936-99 
2776-80 
2693-97 
2645 - 22 
(2) 6162-46 
3973-89 
3487-76 
3286-26 
3181-40 
3117-74 
6122-46 
3957-23 
3474-98 
3274-88 
3170-23 
3107-96 
6102-99 
3949-09 
3468-68 
3269-31 
3166-95 
3101-87 
MgP 15028-3, 7656-6 ±1, 6315-6, 5783-4 
19856-9 
CaP= 19917-5, 9694-5 ? 
19946-8 
* This is the same as finding So from the actually observed lines allocated to So. 
