PART II. 



OF THE THEORY OF DEW. 





DEW, according to Aristotle*, is a species of 

 rain, formed in the lower atmosphere, in conse- 

 quence of its moisture being condensed by the 

 cold of the night into minute drops. Opinions 

 of this kind, respecting the cause of dew, are 

 still entertained by many persons, among whom 

 is the very ingenious Mr. Leslie of Edinburgh f. 

 A fact, however, first taken notice of by Gers- 

 ten, who published his treatise on dew in 1733, 

 proves them to be erroneous ; for he found, that 

 bodies a little elevated in the air often become 

 moist with dew, while similar bodies, lying on 

 the ground, remain dry, though necessarily, 

 from their position, as liable to be wetted, by 

 whatever falls from the heavens, as the former. 

 Shortly after the appearance -of Gers ten's 

 treatise, Musschenbroek made the remark, 

 already mentioned in this Essay, that metals 

 will be free from dew, while other bodies attract 

 it copiously. This philosopher contented himself 



* Meteor. Lib. 1. c. x. et De Mundo. c. iii. 



f Relations of Heat and Moisture, p. 37, and 132. 



N 



