,f. 



14 



M AT H E M A T I C A I 



AND 



S, 



\ 



to a conficlerable diftance, as on the top of a high moun- 

 taui, is always in a freezing ftate within the torrid zone. 



Let us lee how tliis theory of the generation of heat 

 may be fubfcrvient to the inhabitants of the cometary 

 world 



It is evident that comets are furrounded with an at- 

 mofphere very different from that , of our globe; the 

 heighthofour atmofphere is hardly fuppofed to exceed 60 

 or 70 miles, while that of a comet Is frequently 8 or 10,000 

 miles. Why fhould they have fuch a weight of atmo- 

 fphere more than us? This is doubtlefs fubfervient tofome 

 very extraordinary purpofe. We may alfo fuppofe with 

 great probability, that the atmofphere of a comet differs 

 greatly from ours. The particles may be fmaller, more 

 fubtile, elaflic, and much more eafily heated, whence the 

 Sun's rays may be enabled to warm fuch an atmofphere 

 eompreffed together by the weight of eight or ten thoufand 

 miles, at a diftance from the Sun, in which we fliould 

 perceive the mofl intcnfe cold. This will explain the man- 

 ner in which the Inhabitants of a comet may be fufficiently 

 warm at their greatefl diftance from the Sun; but if they 

 were proportionably heated on their nearefl approach 

 to the Sun, their fummer heats would be intolerable; but 

 this mufl certainly be the cafe if their atmofphere were in a 



permanent flate, and continued in all fcafons of equal den- 

 fity and weight. We are certain however from obferva- 



tion, that this is not the cafe; for as the comet approaches 

 the Sun, we can eafily perceive its atmofphere greatly 

 rarified, and thence rendered lefs fit for generating or re- 

 taining heat. But this is not the principal relief which 

 cometarlans receive from the fummer's heat. The atmo- 

 fphere of a comet feems to undergo a change which is pe- 

 culiar to itfelf. It is removed by the rays of light, and 

 thrown off to a confiderable diftance behind the planet. 

 It is demonftrable that the rays of light pafs with amazing 

 velocity, they travel above thirteen millions of miles in a 

 minute; fuch amazing velocity multiplied into their weight, 



however 



? - 



^^ 



^, 



