150 
SIE DAVID BEEWSTEE AXD DE. J. H. GLADSTOXE OX 
remarkable line in the orange, of which much will be said hereafter. The exti’eme 
violet is lettered, both in this and in a map to be subsequently described, by that con- 
tinuation of the alphabet which has been adopted by M. Becqueeel^. It was necessary 
to indicate in some similar manner the newly published, though not newly discovered, 
lines at the red end of the spectrum ; and as the alphabet has not been appropriated by 
M. Becquerel beyond P, and it is not likely that further research will largely extend 
the spectrum in that direction, it was thought safe to take the end of the alphabet, and 
derroting the first strongly-marked fine before A by Z, to work backwards into those 
slightly refrangible rays, which have been as yet unresolved by human vision. Some of 
the dark spaces of the spectrum are of an appreciable breadth, in which case they are 
represented as bands ; and where the observation of a line was indistinct or uncertain, it 
is marked by an interrupted instead of a continuous line. 
The light less refrangible than A is red but extremely faint, so faint indeed, that few 
observers of the spectrum have perhaps ever seen it; and the only di’awing hitherto 
published of lines in it, appears to be in a map of the solar spectrum by M. Matthiessex 
of Altonaf . He represents a few lines which, on comparison -with fig. 1, may be iden- 
tified as the band anterior to Y, Y itself, and the band Y 1. In order to map the lines 
and bands in this portion of the prismatic image. Sir David Brewster was obliged to 
take extraordinary precautions. The telescope was lined with black velvet, in order to 
exclude any refiected light ; a low power was employed ; the sht was made about the 
8th or 10th of an inch wide, and the eye of the observer was washed with water to 
cleanse the fiuid that lubricates the cornea J. The most prominent line in this space is 
that marked Y. 
The red space between A and B is marked by Frauxhofer merely by a bundle of 
lines midway between the two, and designated a. It is indeed difficult to resolve the 
light that extends from A to a, but between a and B lines and bands are easily per- 
ceptible. This space is delineated not only in fig. 1, but on a larger scale in fig. 2, while 
fig. 3 is a still more magnified view of the bundle of hires that constitute a. The 
succession of pale thin bands between A and a 1, represented in fig. 2, were only 
distinctly seen on one occasion ; and to the drawing Sir David Brewster appends the 
remark, “their exact places and breadths require to be better fixed.” They usually 
present themselves to the observer as two or three broader bands, filling up nearly the 
whole space. The series of bands marked by faint lines between a 3 and B, is a peculiar 
feature of this part of the spectrum. 
Between B and C little can be detected with certainty beyond the four lines preiiously 
observed by Frauxhofer. The orange space between C and D is far richer ; but imme- 
diately beyond the double line D is a yellow space of considerable breadth marked by 
only one, and that a faint line, and this is the most luminous portion of the whole 
spectrum. 
* Bibl. Dniv. de Greueve, xl. 
J See Coraptes Eendus, 1850, tom. xxx, p. 579. 
t Eeferred to iu Compt. Eend. xix. p. 112. 
