PROF. A. FOWLER ON SERIES LINES IN SPARK SPECTRA. 
245 
and 4th orders of the grating, and careful measurements have shown that the A 4390 
d doublet is slightly wider (0'3) than the neighbouring doublet of the s series. 
Lorenser’s interval for the second d pair is also greater than that of the other doublets 
which have been measured. The intervals of the remaining pairs have been less 
accurately determined and cannot be used for such a comparison. As in the case of 
the corresponding line A 2798 of the Wide doublet (D) series, the observations of the 
A 4390 doublet suggest a satellite on the more refrangible side of the chief line, and 
this unusual position would accord with the greater strength of the more refrangible 
components of the “ 4481 ” series. 
The “ 4481 ” series may accordingly be considered to be associated with either of the 
two systems of doublets, but a more direct connection with the “ F.P.” group is 
indicated by the fact that these lines occur under precisely the same experimental 
conditions as 4481. With this relation no difficulty arises with regard to the small 
interval of the “ 4481 ” lines, or to the limits of the series when compared with the 
corresponding figures for Ca, Sr, and Ba. It may therefore be concluded that the 
“ 4481 ” series is the Fundamental series of the “ F.P.” system. 
§ 8. The Principal Series of the New Doublet System. 
Associated with the “ F.P.” doublets a Principal series would also be expected. The 
approximate formula for the more refrangible components of these doublets, calculated 
in the usual way from that of the s series, is 
p (on) — 51,328’2 — 
4 x 109,679'3 
(m+ P286480) 2 ’ 
This indicates the neighbourhood of A 9340 for the first p doublet (which should 
have Sn = 30 - 5) and A 3643 for the second. The first is outside the range of the 
present observations, but the second is probably represented by one of two similar 
pairs of lines which are developed under the same conditions as the “ F.P.” lines. In 
each pair the more refrangible component is the stronger, as it should be in the p series, 
and the separations are about that which would be expected in the second member. 
Particulars of these lines are as follows :— 
A(I.A.). 
n. 
Sn. 
3850-40 
25,964-1 
14'6 
3848-24 
25,978-7 
3615-64 
27,650-0 
14-0 
3613-80 
27,664-0 
Remarks. 
Probable “combination” doublet (Plate 3, fig. 8). 
Probable p doublet. 
It is evident that both pairs cannot belong to the p series, and the near equality of 
