232 ESSAY 



conduction. It will be also sooner dewed than 

 another very small plate suspended in the air; 

 since the latter, like other small bodies similarly 

 placed, must be continually acquiring more heat 

 than the former, in the manner described above 

 in this Essay *. 



A piece of metal, applied to different por- 

 tions of cold grass in succession, will sooner be- 

 come cold itself, than another piece, which is 

 suffered to remain constantly upon one portion 

 of the same grass, and will in consequence be 

 sooner dewed. 



If the bare side of a piece of metalled paper 

 be exposed to a clear and calm sky at night, it 

 will become cold, by radiation, and receive, by 

 conduction, the heat of the inferior metallic 

 surface ; whence, if this surface be afterwards 

 made the upper one, it will sooner acquire dew 

 than a similar metallic surface, which has been 

 exposed to the sky during the whole of the ex- 

 periment. 



When a metal covers, in part only, the upper 

 surface of a piece of glass, the uncovered por- 

 tion of the glass quickly becomes cold by radia- 

 tion, on exposure to $ serene sky in a still night, 

 and then, by deriving to itself a part of the heat 

 of the metal, occasions this body to be more 

 readily dewed, than if the whole of the exposed 



* Page 213. 



