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XIII. Carbon and Carbo-Hydrogen, Spectroscoped and Spe- 

 trometed in 1879. By Piazzi Smyth, Astronomer Royal 

 for Scotland*. 



ri^HE recent spectroscopic observations of Brorsen's Comet 

 J- having brought again into view the strange contradiction 

 which still exists, between chemists on one side, and most spec- 

 troscopists on the other, touching the temperature at which 

 pure carbon vapour can possibly be volatilized, the present 

 may be an appropriate occasion for describing a few recent 

 steps in the inquiry, especially as they may haply be found 

 to shed some new light on the difficulty undoubtedly inherent 

 in the case. 



On the one hand, the chemists are represented as uniformly 

 agreed that pure carbon is, to all their methods of trial by 

 furnace- heat, next to impossible to drive off into vapour. And, 

 on the other hand, not only some, but I am told that almost 

 all the great spectroscopists of the day have found, according 

 to their examinations of precision, that the vapour of carbon 

 is given off freely in the moderate heat of every kind of little 

 candle- or lamp-flame (!) — this being evidenced to them by a 

 spectrum which they declare is that of pure carbon, though 

 some two or three persons in, by this time perhaps rather to 

 be considered out of, the community, persist in holding it to 

 be the spectrum of only the compound gas " carbo-hydrogen." 



This last spectrum, carefully described by Professor Swan, 

 in Edinburgh in 1856, as being that of "carbo-hydrogen," 

 was nine years later pronounced by Dr. Attfield in London 

 to belong to pure " carbon," and has now, after many inter- 

 vening researches by other men, very recently been still more 

 minutely examined by me in its most standard form of a coal- 

 gas and common-air blowpipe-flame, viewed end on. This 

 mode of observing it is of extraordinary advantage for seeing 

 the fainter lines, and allowing higherdispersive power of prisms 

 to be employed. But it did not actually reverse any thing of 

 moment in Professor Swan's primary description. It only 

 extended and added details — utilizing even most of the mere 

 haze which earlier observers had noticed hanging about the 

 bands of graduated lines, by resolving it into little attendant 

 lines or linelets. Hence there is no dispute about all the chief 

 physiognomy of this spectrum ; and the only difference of 

 opinion is, the rather extreme case in physics, as to whether it 

 belongs to the easily volatile compound " carbo-hydrogen," or 

 the most refractory and involatile element " carbon." 



* Communicated by tlie Author. 



