1889.] of the various Species of Heavenly Bodies. 163 



his observations on the Great Comet (6) 1882 (date of perihelion 

 passage September 27th) on November 1st, was the low- temperature 

 fluting of magnesium at 500. By that date the D line and the carbon 

 flutings had passed their maximum intensity, and had begun to fade 

 out. 



The same fluting was also seen by Yogel in Coggia's Comet (IV, 

 1874) as a bright line at about 499, when the comet was yet a month 

 from perihelion, and when therefore the appearance of the low- 

 temperature characteristic of the magnesium spectrum would be 

 expected. 



It is fair to myself to say that I was not aware of these observa- 

 tions when I began my recent researches. The fact of the line at 

 500 remaining alone in Nova Cygni, however, made it clear that if 

 my views were correct, the same thing should happen with comets. 

 It now turns out that the crucial observation which I intended to 

 make was made more than twenty-two years ago. 



This spectroscopic evidence is of the strongest, but it does not 

 stand alone ; comets at aphelion present the telescopic appearance for 

 the most part of globular nebulas. 



If it be taken as generally accepted that comets are of nebulous 

 origin, it must be remembered that there are no visible nebulas near 

 enough to our system to supply this material. Prior, therefore, to the 

 effects produced by solar or planetary attraction, the material was in 

 a state of repose ; there were no collisions, and therefore no luminosity. 

 It is not surprising, then, that the faintest comets and the faintest 

 nebulas should both, as a rule, be of globular form. 



Carbon Radiation. 



It is well known that comets generally give us the spectrum of 

 carbon at some time or another on their journey to and from the sun. 

 The question arises, is there any evidence that when at some dis- 

 tance from the sun the carbon phenomena observed indicate a low- 

 temperature ? Is the presence of low-temperature magnesium asso- 

 ciated with low-temperature flutings of carbon ? 



In my paper* of November 17th, 1887, I gave a map showing the 

 two sets of flutings, and one to show low and high temperatures. 

 The brightest edges of the three principal flutings in the low-tempera- 

 ture spectrum are at wave-lengths 519' 7, 560*7, and 483*3, and those 

 in the high- temperature spectrum are at 516*4, 563'3, and 473*6. 

 The two first flutings in each of the two spectra fall pretty near to 

 those in the other, and a considerable degree of accuracy, which has 

 not in a great number of cases been attained in the observations of 

 cometary bands, is therefore necessary before we can say with abso- 



* ' Eoy. Soc. Proc.,' vol. 43, p. 132. 



