

Observations of a Comet. 67 



of the comet cannot be accounted for from reflection, we 

 may draw the same conclusion, with respect to the bright- 

 ness of the head, coma, and tail, from the following consi- 

 deration. The observation of the 2d of February mentions, 

 that not only the head and coma were still Very bright, but 

 that also the faint remains of the tail were still visible ; but 

 the distance of the comet from the Earth, at the time of 

 observation, was nearly 240 millions of miles*, which 

 proves, I think, that no light reflected from floating parti- 

 cles could possibly have reached the eye, without supposing 

 the number, extent, and density of these particles far greater 

 than what can be admitted. 



My last observation of the comet, on the 2 1st of February, 

 gives additional support to what has been said ; for at the 

 time of this observation the comet was almost 2*9 times 

 the mean distance of the sun from the Earth f. It was also 

 nearly 2*7 from the sun J. What chance then could ravs 

 going to the comet from the sun, at such a distance, have 

 to be seen after reflection, by an eye placed at more than 

 275 millions of miles § from the comet? And yet the in- 

 stant the comet made its appearance in the telescope, it 

 struck the eye as a very conspicuous object. 



The immense tails also of some comets lhat have been 

 observed, and even that of the present one^ the tail of which, 

 on the 18th of October, was expanded over a space of more 

 than nine millions of miles ||, may be accounted for more 

 satisfactorily, by admitting them to consist of radiant mat- 

 ter, such as, for instance, the aurora borealis, than when 

 we unnecessarily ascribe their light to a reflection of the sun's 

 illumination thrown upon vapours supposed to arise from 

 the body of the comet. 



By the gradual increase of the distance of our comet, we 

 have seen, that it assumed the resemblance of a nebula; 

 and it is certain, that had I met with it in one of my sweeps 

 of the zones of the heavens, as it appeared on either of the 



* 239894939. 



f The sun's mean distance being 1, that gJ" the comet was 289797. 



\ The comet's distance Irom the sun was 2*669100. 



§ 27i077Sb«<. || 9160542. 



E 2 days 



