IN CONNEXION WITH THE SPECTRUM OF THE SUN. 
657 
Explanation of the Plates. 
PLATE LI. 
Upper Half. 
Spectra of strontium salts in air with low-tension spark. 
A, spectrum of Sr I 2 . 
B, 
C, 
D, 
E, 
55 
55 
55 
55 
55 
55 
55 
55 
Sr Br 2 . 
Sr Cl” 
Sr pj 
metallic strontium. 
Notes . — Some of the lines in the red in the spectrum of strontic fluoride are seen, but 
the “ structure ” of the compound spectrum renders it difficult to decide which. 
The structure (for the first three salts) is at first exceedingly brilliant and varies with 
each salt, but after a time it gets dimmer and is the same for all salts. 
The brilliant compound spectrum renders the presence of the lines at W. L. 5970-5 
and 5850-0 in the salts very doubtful. 
The line 4226-3 has since been proved to belong to calcium. 
The line 4161-0 is always very faint. 
Lower Half. 
Spectra of lead salts in air with low-tension spark. 
A, spectrum of Pb I 2 . 
B, „ „ Pb Br 2 . 
C, „ „ PbCl 2 . 
D, „ „ Pb F 2 . 
E, „ „ metallic lead. 
Notes . — The line 6452-0 was very faint and difficult of observation in Pb F 0 . 
The line 5163-0 is coincident with an air line, and its length is uncertain in the 
metallic spectrum, though it is brilliant. It is, however, long in the salts. 
The lines 4386 - 5 and 4246-0 only appear for a short time in the spectrum of PbE 2 , 
though the time is longer than in the other salts. In Pb I 2 they flash in and instantly 
vanish ; in Pb Cl 2 they vanish nearly as quickly. 
The line 4062-5 is faint; it is probably not a lead line. 
4058-0 is the longest line. 
