244 
PROF. A. FOWLER ON SERIES LINES IN SPARK SPECTRA. 
the wave-lengths of which have been redetermined from plates taken in the 3rd and 
4th orders of the grating. International standards were employed in the determina¬ 
tions but the wave-lengths on both scales are given in Table VII. 
For these “F.P. doublets the small letters d , s, andy> will be used for the Diffuse, 
Sharp, and Principal series respectively, D, S, and P being reserved for the 
corresponding series of Wide doublets. 
Employing the less refrangible components of the first, second, and fourth doublets 
for the calculation of constants, the resulting equation for the d series is 
d (m) — 
40,618'45 / 
40,648-95/ 
4x 109,679-3 
m + 0-947218 + 
Q'042317 
m 
\ 2 
and for the s series, assuming the same limits and calculating from the first and third 
of the less refrangible components 
s (m) 
40,618-45/ 
40,648-95/ 
4 x 109,679-3 
m + 0‘930,683 — 
0"014220\ 2 
m 
These equations represent all the observations very closely as will be seen from the 
columns “ O —C ” in Table VII. 
§ 7. Relation between the “ 4481 ” and the New Series. 
A connection between the “ F.P.” doublets and the “ 4481 series is indicated by 
the above equation for the d series, since rn — 2 gives the variable part as 49,790"5 
which is very close to the limits of the “4481 ” series. By analogy with the doublets 
of Ca, Sr, and Ba, this would be the case if the “4481 ” series were a Fundamental 
series forming part of the “F.P.” system. Such an association would conform with 
the rule already indicated by the other three elements that the limit of the 
Fundamental series in the case of enhanced lines is derived from the first negative term 
of the d series, and not from the first positive as in arc line series. 
For the complete establishment of this relation the lines of the d series should be 
found to have satellites; and in the case of the first member the separation of the 
satellite should be equal to that of 4481. The wave-length of the first line is given by 
the Hicks formula as near X 10,900, a position which does not fall within the region 
which could be observed with the instruments available. The satellite separation 
should be SX — 1"2. The second d pair (\ 7896), which should have a satellite 
separation c>\ = 0'25, is also outside the region investigated. At the third (X 4390"6) 
the satellite separation would be reduced to SX = 0"04 (Sn = 0'2l) which is too small 
for resolution. There is, however, some evidence of a disturbance of the position of 
the third line (Table VII.). This part of the spectrum was photographed in the 3rd 
