Comets. 251 



of 1744 had no less than six, spread out like an immense 

 fan, extending to a distance of nearly 30° in length. The 

 small comet of 1823 had two, making an angle of about 160°, 

 — the brighter turned as usual from the sun ; the fainter, 

 towards it, or nearly so. The tails of comets, too, are often 

 somewhat curved, bending, in general, towards the region 

 which the comet has left, as if moving somewhat more slowly, 

 or as if resisted in their course. 



The smaller comets, such as are visible only in telescopes, 

 or with difficulty by the naked eye, and which are by far the 

 most numerous, offer very frequently no appearance of a tail, 

 and appear only as round or somewhat oval vaporous masses, 

 more dense towards the centre, where, however, they ap- 

 pear to have no distinct nucleus, or anything which seems 

 entitled to be considered as a solid body. Stars of the small- 

 est magnitudes remain distinctly visible, though covered by 

 what appears to be the densest portion of their substance ; 

 although the same stars would be completely obliterated by 

 a moderate fog, extending only a few yards from the surface 

 of the earth. And since it is an observed fact, that even 

 those larger comets which have presented the appeai-ance of 

 a nucleus have yet exhibited no phases ; though we cannot 

 doubt that they shine by the reflected solar light, it follows 

 that even these can only be regarded as great masses of thin 

 vapour, susceptible of being penetrated through their whole 

 substance by the sunbeams, and reflecting them alike from 

 their interior parts and from their surfaces. Nor will any 

 one regard this explanation as forced, or feel disposed to re- 

 sort to a phosphorescent quality in the comet itself, to ac- 

 count for the phenomena in question, when we consider (what 

 will be hereafter shewn) the enormous magnitude of the 

 space thus illuminated, and the extremely small 7nass which 

 there is ground to attribute to these bodies. It will then 

 be evident that the most unsubstantial clouds which float in 

 the highest I'egions of our atmosphere, and seem at sunset 

 to be drenched in light, and to glow throughout their whole 

 depth as if in actual ignition, without any shadow or dark 

 side, must be looked upon as dense and massive bodies, com- 

 pared with the filmy and all but spiritual texture of a comet. 



