ON TWO CELESTIAL BODIES. 143 



them fo far the refemblance of comets, that in this refpect we 

 fhould be rather inclined to rank them in that order, did other 

 circumftances permit us to aflent to this idea. 



In the feventh article, they are again unlike planets ; for it 

 appears, that their orbits are too near each other to agree with 

 the general harmony that takes place among the reft ; perhaps 

 one of them might be brought in, to fill up a feeming vacancy 

 between Mars and Jupiter. There is a certain regularity in 

 the arrangement of planetary orbits, which has been pointed 



out by a very intelligent aftronomer, fo long ago as the year 

 1772 ; but this, by the admiffion of the two new ftars into the 



order of planets, would be completely overturned ; whereas, 



if they are of a different fpecies, it may ftiil remain efta- 



bJiflied. 



As we have now fufficiently fhewri that our new ftars can- The new ftars 



not be called planets, we proceed to compare them alfo with are uot P anets » 



the other propofed fpecies of celeftial bodies, namely, comets. 



The criteria by which we have hitherto diftinguifhed thefe 



from planets, may be enumerated as follows. 



1 . They are celeftial bodies, generally of a very fmall fize, Criterions of 



though how far this may be limited, is yet unknown. ""The are 



. 2. They move in very excentric ellipfes, or apparently para- fmall. 



bolic arches, round the fun. centric^ **' 



3. The planes of their motion admit of the greateft variety 3 . pj a n es ^ 

 in their fituation. rious ! 



4. The direction of their motion alfo is totally undetermined, various. 



5. They have atmofpheres of very great extent, which fhew5» Great atmo- 

 themfelves in various forms of tails, coma, hazinefs, &c. p eres * 



On calling our eye over thefe diftinguifhing marks, it ap- Companion of 

 pears, that in the firft point, relating to fize, our new ftars Seferefpeft!. 511 

 agree fufficiently well ; for the magnitude of comets is not 

 only fmall, but very unlimited. Mr. Pigott's comet, for in- 

 ftance, of the year 1781, feemed to have fome kind of nucleus; 

 though its magnitude was fo ill defined, that I probably over- 

 rated it much, when, November 22, I guefTed it might amount 

 to 3 or 4" in diameter. But, even this, confidering its near- 

 nefs to the earth, proves it to have been very fmall. 



That of the year 1783, alfo difcovered by Mr. Pigott, I faw 

 to more advantage, in the meridian, with a 20-feet reflector. 

 It had a fmall nucleus, which, November 29, was coarfely 

 eftimated to be of perhaps 3" diameter. In all my other pretty 



numerous 



