152 ESSAY 



SECTION II. 



Of the Cold connected with the Formation of Dew* 



DEW is often spoken of as being cold, by 

 popular writers. Thus Cicero and Virgil apply 

 to it the epithet of 'gelidus,' Milton that of 

 ' chill/ and Collins that of cold/ Of the same 

 import is a passage in Herodotus, in which it is 

 said, that, in Egypt, the crocodile passes a great 

 part of the day on dry land, but the whole of 

 the night in the Nile, this being warmer than 

 the atmosphere, and the dew. Among philoso- 

 phers, however, Mr. Wilson was the first, I be- 

 lieve, who ever suspected the existence of such 

 a conjunction. 



In my experiments on the temperature of 

 bodies moistened with dew, small thermometers 

 were employed, (the largest being only 8 inches 

 long) having globular bulbs, which, in most of 

 them, were not more than from 2 to 2|- lines in 

 diameter. Their scales, which were marked in 

 the manner of Fahrenheit, were of ivory or 

 wood, and were furnished, almost all of them, 

 with hinges. They were always employed 

 naked, except I wished to know the effect of 

 covering them with any particular substance. 



By means of these instruments I have very 



