186 Mr. J. N. Lockyer. On the Classification [Jan. 10, 



consequently (most probably in a different part of the comet) on the 

 red ward sides of the bright ones. 



VI. GENERAL STATEMENT WITH REGARD TO CARBON. 



The earliest spectroscopic observations of comets showed that 

 carbon was a very important element in cometary spectra. Since 

 then, as we have seen, carbon has also been recorded in almost every 

 comet which has been observed, although the spectrum is often 

 greatly modified by the presence of other substances. The experi- 

 ments on the spectrum of carbon which I commenced many years ago, 

 but which have been temporarily discontinued, show that there are 

 several distinct stages in the spectrum of carbon. At very low 

 temperatures all compounds of carbon give a spectrum consisting of 

 what I have already referred to as the cool carbon flutings. A 

 higher temperature gives what I have called the hot carbon flutings, 

 or carbon A. Finally we get the line spectrum of carbon. Another 

 condition, which is not yet completely understood, is marked by the 

 appearance of the group beginning at 460, which I have called 

 carbon B.* Associated with this are the groups beginning at 420 and 

 388, the relations of which to the line spectrum I have already 

 discussed in a communication to the Royal Society ;f 1 here repro- 

 duce a diagram, fig. 11, which 1 then gave, showing this relation. 



Fig. 11. Diagram showing the relation to temperature of the carbon line and the 

 violet and ultra-violet carbon B groups. The top horizon indicates the highest 

 temperature. 



In the majority of cases the spectrum of a comet has not been 

 recorded until it has arrived at the hot carbon condition, but in the 



* JBakerian Lecture, p. 57. 



f ' Roy. Soc. Proc.,' vol. 30, p. 461. 



