ON ATMOSPHERIC PHENOMENA. J 13 



being a substance that belongs to the atmosphere of the atmospher* 

 Sun, and is foreign to ours and those of other planets; at 

 which it arrives only by virtue of the great elasticity it pos- 

 sesses when in the state of light, and where it is retained 

 only by its adhesion to substances that belong to these pla- 

 nets ; must resume the state of light, the moment when p 

 having arrived at the utmost limits of these foreign atmo- 

 spheres, and being disengaged from the substances that can 

 no longer follow it, it returns to that which is proper to it, 

 and there takes a centripetal motion, or movement of ap- 

 proximation to the Sun ; which, being a perfectly transpa- 

 rent and elastic substance, occasions it to take an opposite 

 course with the same velocity, with which it rushed upon it, 

 which must occasion a perpetual circulation of light be- Perpetual cit- 

 tween the Sun and those globes, that make part of its sys- C . U ] :1U011 of 

 tern. 



If this were not the true state of things, there would be Otherwise an 

 an incessant accumulation of caloric, that would soon accumulation 

 change the face of these globes; while in this hypothesis eha'rgethefat* 

 the equilibrium is scarcely ever interrupted. These globes of things, 

 then would not be visible but from the extreme limits of 

 their atmospheres, and where the caloric, separated from its 

 combinations, is transformed into light : and the opacity of 

 a globe would not at all prevent this effect, in which the 

 globe itself would not interfere; which would make a won- and our astro- 



derful difference in the calculations, from which we have noTTHcal calcu- 

 lations would 

 determined the apparent magnitudes of the celestial bodies; be erroneous. 



as in this case their magnitudes would have been Calculated 

 from the extent of their atmospheres, and by no means 

 from that of the globes or celestial bodies themselves ; and 

 the light, which renders these bodies visible to us, would 

 not be reflected light, but light extricated from them, or re- 

 turning toward the Sun; It is to be understood, that this The presence 

 extrication cannot take place, except as far as the atmo- e bun n«- 



1 , ' r _ cessary to at* 



sphere faces the Siin, and is under the direct influence of tract this light, 

 its attractive power; otherwise the light extricated would 

 diffuse itself through space, take a course different from 

 that to the Sun, and not reach the atmosphere of that ce- 

 lestial body, where alone it can resume its character of light. 

 Nothing prevents the light in this return from traversing 

 Vol. XXIV~Qct. 180£>. I *th« 



