PHYSICAL AND LITERARY. 6^ 



the jnediitm of emiffion into the given 

 medium, 



QuER. IV. If the atmofphere is not much 

 warmed by the palTage of the fun's hght 

 thro' it, but chiefly by its contad; with the 

 iieated furface of the globe, as we fhewed 

 ■above (N° 15.); may we not hence give 

 one very fimple and plaufible reafon, why 

 it is coldeift in all climates on the tops of 

 very high mountains ; namely, becaufe they 

 are removed to the greateft diftance from the 

 general furface of the earth ? For it is well- 

 known, that a fluid heated by its-conta<ft 

 with a folid body decreafes in heat, ift fome 

 inverfe proportion to the diftance from the 

 body. But, to have this quefl:ion fully de- 

 termined, the temperature of the. air in the 

 valley and on the mountain-top muft be ob- 

 ferved every hour both night and day, and 

 carefully compared together. 



QuER. V. From what has been laid dowrj 

 in Se(£l ii. concerning the manner of the 

 aftion of Hght in heating bodies, is it not 

 reafonable to fuppofe that the heat produced 

 by a given number of rays, in an opaque 

 body of a given magnitude, mufl: be greater 



wh«» 



