230 
PROF. A. FOWLER ON SERIES LINES IN SPARK SPECTRA. 
previous paper. The reference spectrum for these lines was the copper arc, as given 
by Kayser and Runge, and the lines are subject to an uncertainty of about 0'05 A.U. 
in absolute value. 
All the necessary details with regard to the “ 4481 ” series are brought together in 
Table I., the corrections to vacuum having been made from Kayser’s table A 
Table I.—The “4481 ” Series of Magnesium. 
A, 
wave-length 
(LA.). 
Estimated 
limit 
of error in 
A. 
sx. 
n, 
wave-number 
(in vacuo). 
Estimated 
limit 
of error in 
n. 
8n. 
Remarks. 
4481-327 
0-005 
22,308-68 
0-025 
From 3rd and 4th order plates. 
0-198 
0-99 
448L129 
0-005 
9-67 
0-025 
3104-805 
0-005 
32,198-99 
0-05 
From 4th order plates. 
0-092 
0-94 
3104-713 
0-005 
9-93 
0-05 
2660-821 
o-oi 
37,571-43 
0-14 
From 3rd order plate. 
0-066 
0-94 
2660-755 
0-01 
2-37 
0-14 
2449-573 
o-oi 
40,811-31 
0-17 
j 
>From 1st order plate. 
2329-58 
0-02 
42,913-30 
0-4 
J 
2253-87 
0-05 
44,354-65 
1-0 
1 
2202-68 
0-05 
45,385-36 
1 -o 
]■ From quartz spectrograph. 
| 
2166-28 
0-05 
46,147-86 
1-1 
J 
From the separations of the three lines which have been resolved, it appears at once 
that the interval between the components, in wave-numbers, is sensibly constant, and 
that the series is therefore not of the ordinary Principal type. In a Principal series 
having a separation of 0'99 for the first member at 4481, the interval at 3104 would 
be reduced to 0'64, and at 2660 to 0'44, but there is no evidence of such contraction. 
§3. Formula for the Mg “4481 ” Series. 
The application to these lines of the ordinary formulas of Rydberg, Ritz, or Hicks, 
requires the division of the lines into two series by taking alternate lines, the two 
* ‘Handbuch der Spectroscopie,’ Band II., p. 514. 
