U ESSAYS AND OBSERVATIONS 



are infleded in^o a curve by the continued 

 infradlon Jirifing from the continual increafe 

 of its denfity ; therefore they muft produce 

 fome degree of heat in every part of their 

 progrefs thro' it [N° lo.]. Bat, as the 

 whole fuccefTive refradidn is juft equal to 

 the fingle refradion that would be made in 

 paffing at once from the celeftiai fpices into 

 a medium as denfe as the loweft part of our 

 atmofphere *, and all the fuccefTive refle- 

 xions that can be made from every different 

 Jlrdtum, are but equal to what would be 

 made at once from the fur face of a medium 

 ' of the fame denfity j it eafily appears, by 

 comparing the denfities of air and water, and 

 their refpedive figns of refradion, that all 

 the refradion and reflexion which the whole 

 depth of our atmofphere produces is much 

 lefs than what happens at one furface of v/a- 

 ter ; and confequently, the heat produced in 

 our atmofphere, by the immediate adion of 

 light upon it, m.ufl likeways be much lefs 

 than what is raifed in water. The air 

 feems to have the greatefl part of its heat 

 communicated to it from ihe opaque vapours 



which 



* Ne'u:t< Opt. book 2. part 2, prop. to. 



