224 
ME. J. ATTFIELD ON THE SPECTEHM OE CAEBON. 
furrowed than in the case of carbonic oxide ; but when ignited by the electric current, 
its spectrum is well defined, and is that of carbon plus that of sulphur. That is to say, 
it is the spectrum of carbon plus the spectrum that is obtained from vapour of sulphur 
w^hen ignited by the electric discharge in an otherwise vacuous tube. 
Having thus demonstrated that dissimilar compounds containing carbon emit, when 
sufficiently ignited, similar rays of light, I come to the conclusion that those rays are 
chamcteristic of ignited carbon vapour, and that the phenomenon they give rise to on 
being refracted by a prism is the spectrum of carbon. 
The spectrum of carbon is a very beautiful one. The lines composing each band of 
light regularly diminish in brightness in the direction of greatest refraction, and appear 
to retreat from the observer like pillars of a portico seen in perspective. It differs 
greatly from that of every other element that I am acquainted with; and though, in 
each of the experiments described, it was of course accompanied by the spectrum of 
either nitrogen, hydrogen, slilphur, or oxygen, its diagnosis was not thereby interfered 
with ; it is, in fact, most widely different from, and cannot possibly be confounded with, 
either of them. 
The brightest band of the carbon spectrum being blue, and its other constituents 
being on the one hand light green and on the other violet, the associated rays of ignited 
carbon vapour, as indeed seen by the naked eye in carbon flames, I conceive to be of a 
light-blue colour. The tint may be observed in the flame of a spirit-lamp, in a burning 
jet of carbonic oxide, in the blowpipe flame of any hydrocarbon, and at the base of a 
common candle flame. I have no hesitation in saying that should a source of heat be 
found of sufficient intensity to volatilize the diamond and ignite its vapour, blue will be 
the colour of the light emitted. 
The subject of the emission of carbon light by carbon vapour naturally leads to the 
consideration of the absorption of carbon light by carbon vapour. This latter research 
I am compelled to defer for a time. 
The investigation also suggests the important question. Is the spectrum of a compound 
simply the sum of the spectra of its constituents^ I have made several experiments 
tending to confirm such a law, but must perform many more before coming to a decided 
conclusion. Some observations made by Professor Plucker in the course of an exami- 
nation of the effects of the electric discharge on rarefied gases * seem to indicate that a 
compound has a spectrum different from that of the superposed spectra of its consti- 
tuents. 
Finally, I beg to offer my best thanks to Dr. Feankland for allowing me the use of 
his laboratory and apparatus in making this research, and to J. P. Gassiot, Esq., and 
Captain G. W. Puget (34th Eegt.) for the loan of induction coils. 
* PoGGEirDOEPi'’s ‘ Annalen,’ Bd. cv. S. 77, and Bd. cyii. S. 533. 
