COMETS. 403 



possible ; instead of deriving their fire and 

 splendor immediately from the sun, I conceive 

 that the fire and splendor which they display, 

 are effects only which are produced by the 

 union which has taken place, between the at- 

 mospheric materials of which they are com- 

 posed, and the solar rays, with which they 

 have combined, that those pure rays ; being 

 destitute of fire altogether, could not convey 

 into the bodies of the Comets, any quantity 

 whatever of fire into them ; and, consequently, 

 that the various calculations that have been 

 made respecting their motion, and situations, 

 from the nature of the materials of which it is 

 supposed they consist, are altogether errone- 

 ous and fallacious ; as erroneous and falla- 

 cious as the supposed limits which have been 

 given to the elevation to which it is conjectured 

 our atmosphere extends. I conceive it as im- 

 possible to measure the extent of it by means 

 of the barometers which are employed, as it is 

 for the barrow-boy in the streets, who sells 

 filberts by the pound, to measure in his scales, 

 the relative densities and weights of the planets 

 Jupiter and Saturn. 



In order to bring my ideas, respecting 

 the nature of fire, to a close, I shall take 

 leave to observe, that I conceive the sun to 

 be neither hot nor cold, but to be consti- 

 tuted of light only ; that the rays which per- 

 petually emanate from the sun as their source^ 



