ASTRONOMICAL PAPERS 



135 



fentially from every other planet or ftar. If I fliould be fm- 

 ular in any part of my opinion on this fubje£t, I prefume 



g 



One imai^ines that comets 



I fliall be indulged, fince it is matter of mere hypothefis. 



Comets are not blazing flars, they do not burn at all, 

 nor is there any remarkable heat in that tail which has fo 

 often terrified the nations, and been thought to portend 

 diifolution to the world itfelf The comet of 1743 had 

 acquired a tail fome thoufands of miles long above two 

 ^Tionths before he paifed the Sun, while he was yet three 

 hundred millions of miles from the Sun. Surely this could 

 not be a flame of fire kindled by the Sun, elfe comets take 

 fire in a place where every drop of water on this globe 

 would inftantly freeze. Thereis nogreater reafon tothink 

 that comets burn by their own heat, fince their tail, what- 

 ever it be, as well as their light, evidently depends on the 

 Sun, as we have already explained. 



Philofophers have differed greatly in their attempts to 



account for the tail of a comet. 



are iurrounded on all fides by a lucid fiery vapour, or at- 



mofphere, which on account of the Sun's fuperior light, 



is only vifible in the dark, whence we fee no part of it but 

 that which is in the fhadow of the comet on the fide op- 

 pofite to the Sun. According to him their atmofpherc 

 extends in all directions feventy or eighty millions of miles, 

 for fome comets have appeared with a tail of that length, 

 fo that from the near approach of comets to the earth we 

 mufl frequently have been enveloped in that fame lucid 



atmofphere. 



From the extreme viciffitudes which comets feem to en- 

 dure, at one time penetrated with intolerable cold, at ano- 

 ther time blazing with deftruftivc heat, fome have Irre- 

 verently conjcdured that they were defignedas a place of 

 future refidencc for the unhappy tranfgrefFors in this flatc, 

 and thus vainly fuppofe that fifty or an hundred worlds 

 were created for the fake of punifhing the inhabitants of 

 this little globe. It is fufficient to have mentioned fuch 

 cpnicdures. 



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