THE TWO COMETS OF THE YEAR 1868. 175 



spectrum, Dr. Huggins determined to compare the two 

 spectra directly. We have not space to explain the 

 contrivances by which this was effected. Suffice it to 

 say, that when the two spectra were brought side by side 

 it appeared that in place of mere resemblance there was 

 absolute identity. The bands of light which formed 

 the comet's spectrum were found not only to coincide 

 in position with those which appeared in the spectrum 

 of olefiant gas, but to present the same relative bright- 

 ness. Two days later the observations were repeated 

 by Dr. Huggins in company with Professor Miller (who 

 had been associated with him in his earlier spectroscopic 

 labours), and both observers agreed in the opinion that 

 the coincidence between' the spectra could not be more 

 exact. 



The reader will, of course, understand that the hydro- 

 gen lines belonging to the spectrum of olefiant gas are 

 not seen in the spectrum of the comet. 



Now only one interpretation can be put on this re- 

 markable result, and that is that Winnecke's comet 

 consists of the incandescent vapour of carbon, not 

 of burning carbon, be it understood, but of volatilised 

 carbon. 



But carbon, as we are acquainted with it on earth, 

 is a substance whose chief peculiarity, perhaps, is its 

 fixity at ordinary temperatures ; and no phenomenon 

 hitherto presented by comets is more perplexing than 

 the existence of volatilised carbon as the main or only 

 .constituent of a comet of enormous real bulk, when 

 that comet was not so near to the sun as to be raised 



