ON DEW, &c. 195 



Regarding now as established, that bodies 

 situated on or near to the surface of the earth 

 become, under certain circumstances, colder 

 than the neighbouring air, by radiating more 

 heat to the heavens, than they receive in every 

 way*, I shall in the first place offer a few re- 

 marks on the extent and use of this occurrence, 

 and shall afterwards apply the knowledge, of it 

 to the explanation of several more of the ap- 

 pearances described in the former part of this 

 Essay, and of some others, which have not 

 hitherto been mentioned by me. 



Which, he saith, will as sensibly reflect the actual cold of snow 

 or ice, as they will the heat of the sun." Boyle's Works, 

 folio, vol. V. p. 345. 



* Count Rumford offered the following conjecture, in a 

 paper printed in the Philosophical Transactions for 1804. 

 fe The excessive cold which is known to reign, in all seasons, 

 on the tops of very high mountains, and in the higher regions 

 of the atmosphere, and the frosts at night, which so fre- 

 quently take place on the surface of the plains below, in very 

 clear and still weather, in spring and autumn, seem to indi- 

 cate, that frigorific rays arrive continually at the surface of 

 the earth, from every part of the heavens." But he gave no 

 experiments to prove, that such a communication actually 

 exists between the heavens and the earth at night. Neither 

 does it appear from any of his writings which I have seen, 

 that he ever supposed, that the surface of the earth is more 

 cooled by these frigorific rays, than the air through which 

 they pass, or that some solid bodies are more cooled by them 

 than others. 



O 2 



