266 
PROF. A. FOWLER ON SERIES LINES IN SPARK SPECTRA. 
Description of Plate. 
The photographs are of the spectrum of the magnesium arc in vacuo. The letters 
indicate the series to which the lines belong, and have the following significance :— 
Enhanced lines 
Arc lines 
P, Principal series 
D, Diffuse ,, 
S, Sharp ,, 
p, Principal ,, 
d, Diffuse ,, 
5, Sharp ,, 
f, Fundamental series 
A, Combination ,, A 
B, ,, „ B 
C, Other combination lines 
Wide doublet system. 
F.P.” doublet system. 
Bydberg series of single lines (Diffuse). 
Bo, ,, ,, ,, ,, (Sharp). 
Tj, Diffuse series of triplets. 
To, Sharp ,, ,, 
1 , 2, 3 show chiefly the two Combination series of enhanced lines and the “F.P.” 
doublets near the Fundamental line X 4481. 
4, 5 show further members of the “ F.P.” system and the Wide doublets in the 
ultra-violet. 
6 , 7 —Grating, 4th order—enlarged about eleven times. X4481 (SX = 0T98) and 
X 3105 (SX = 0'092) respectively, each with a longer and a shorter exposure. 
8, the “ F.P.” Combination doublet (X3850, X 3848) near the Diffuse triplet. 
Lines of impurities — Na, Hg, Ca, Ba, H. 
Bands of magnesium hydride (5211, 4802). 
PRESENTED 
14 SEH 1914 
