150 PROFESSOR A. 8. HERSCHEL ON 
APPENDIX III. 
ON THE MAGNIFICENT FEATURES EXHIBITED BY END-ON VIEWS OF 
GAS-SPECTRA UNDER HIGH DISPERSION. 
By Professor A. S. Herscuer, M.A., F.R.A.S. 
I have enjoyed rare and exceptional opportunities during the last two years of often 
beholding, although with very little leisure for studying them minutely, the splendid spectacles 
presented by fluted and other spectra of incandescent gases in the optically exquisite, and 
surpassingly powerful compound-prism spectroscope erected by Professor Piazzi SmytTH for 
examining Aurore. 
My first views through the instrument, in April 1878, were chiefly confined to detecting 
and observing impurities of the rarefied gases said to be contained in the fine series of lateral 
view Geissler-tubes which Professor P1Azz1 Smytu had obtained from the late Mr GEISSLER 
himself, for his investigations. The admirable disposition of the pointer, and means of pro- 
ducing and shutting off immediately, close to the upper and lower edges of a spectrum under 
examination the spectra of comparison tubes, combined with the extraordinary dispersion and 
transparency of the prisms, and the precision and solidity of all the movements and adjust- 
ments, made this first reconnaissance of the apparatus no laborious investigation, but on the 
contrary a brief enjoyment of the most unexampled luxury of ease and celerity in ocular 
discriminations which can very well be desired or arrived at with the spectroscope. 
Among my numerous notes of this first acquaintance, it will suffice to mention as an 
important observation, that the bands of carbon received especial attention; and that their 
individual variations in strength from tube to tube (for scarcely any tube seemed to be free 
from them), unaccompanied by any visible alterations of their positions, is a subject which well 
merits the foremost share of recognition in a circumstantial description. 
It is well known that the blow-pipe-flame green, citron, and orange bands differ in the 
spectral places of their leading edges and shaft-lines from the corresponding carbon band-edge 
positions observed with the extraordinary ubiquity just described in vacuum tubes. Super- 
posed upon the vacuum-tube carbon-hbands they yet in general also exhibit their comple- 
mentary array with a varying degree of strength, more or less prominently, as intruders. These 
two distinct orange-citron-green confederations certainly have an independent origin. One of 
the two is absent and not at all discernible in the blow-pipe-flame, while in almost every 
vacuum tube it can either be traced perceptibly, or it is even troublesomely conspicuous ; and 
it is especially resplendent in tubes of carbonic oxide and carbonic acid. If it is anywhere 
very much subdued, it is so principally in an olefiant-gas vacuum tube, where the tricoloured 
