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IX. On the Lines of the Solar Spectrum. 
By Sir David Beewster, K.H., D.C.L., F.B.S. L. & E., and Br. J. H. Gladstone, F.B.S. 
Eeceired January 26, — Bead February 23, 1860. 
In a paper published in the Transactions of the Royal Society of Edinburgh for 1833, 
Sir David Brewster stated that by various means he had examined the lines of the 
solar spectrum, and those produced by the intervention of nitrous acid gas, and had 
delineated them on a scale four times greater than that employed in the beautiful map 
of Fraunhofer. Some portions also, which were more particularly studied, had been 
drawn on a scale twelve times greater. “Fraunhofer,” he continued, “has laid down 
in his map 354 lines, but in the delineations which I have executed, the spectrum is 
dmded into more than 2000 \isible and easily recognized portions, separated from each 
other by hnes more or less marked, according as we use the simple solar spectrum, or 
the solar and gaseous spectrum combined, or the gaseous spectrum itself, in which any 
breadth can be given to the dark spaces.” None of these drawings, however, were 
published at the time. Frequent observations were continued during the years 1837, 
1838, and 1841 ; and now, after a lapse of many years, the various delineations, having- 
been collated and arranged by Dr. Gladstone, form the principal diagrams in the Plate 
accompanying this paper. 
Fig. I of Plate lY. represents the lines observed when the sun was at a considerable 
altitude above the horizon, and its light was examined by means of a good prism 
and telescope. The spectrum is delineated on so large a scale that it was necessary 
to di\ide it into two portions, the upper diagram representing the part between the 
least refrangible end and the line designated F 7, the lower diagram the part between 
F 7 and the most refrangible end. On a comparison with Fraunhofer’s large map *, 
the principal lines and features will be easily recognized ; but it will be seen that 
every portion of the spectrum contains lines wanting in the earlier drawing, and that 
parts which Fraunhofer has marked by one line are resolved into groups of bright 
spaces alternating udth dark lines. The figure of the spectrum extends at the more 
refrangible or Yolet end to about the same distance as that of the Bavarian philosopher, 
but it exhibits a considerable extension at the red or less refrangible end. The 
principal lines are indicated by those letters. A, a, B, C, &c., which were assigned to 
them by him, and the larger intermediate lines are marked by numbers, I, 2, 3, &c., 
beginning afresh on the more refrangible side of each letter ; so that any one of these 
may be expressed by a combination of a letter and numeral ; as, for instance, C 6, a 
* In his “ Bestimmung des Brechiings- und Barbenzerstreunugs-Verindgeiis verschiedener Grlasarten.” 
MDCCCLX. X 
