240 ESSAY 



possessed, in common with other parts of the 

 atmosphere. Dufay attempted to strengthen 

 his argument, by exposing, on three dewy 

 nights, similar substances at different heights 

 from the ground, expecting that the lower 

 would always acquire more moisture than the 

 upper ; but, upon all the nights, some one of 

 the lower substances acquired less moisture, 

 than some one of the higher. 



Mr. Webster has advanced no new fact in 

 favour of the opinion, of which I am speaking. 



Enough having been said to prove, that dew 

 is not entirely the product of vapour rising from 

 the earth at night, I shall next show, that it 

 often occurs, when this cause can have little or 

 no operation. 



1. It appears from Hasselquist and Bruce, 

 that in Egypt, shortly before the rising of the 

 Nile, and consequently when the ground there 

 is in its driest state, dew becomes exceedingly 

 plentiful, though little or none had formed be- 

 fore, while the earth was somewhat less dry. 

 The cause evidently is, as was formerly men- 

 tioned, the moist air brought from the Me- 

 diterranean by the north wind, which then 

 prevails. 



52. Mr. Webster, speaking of hoarfrost, which 

 he properly regards as frozen dew, candidly 

 says, though it overthrows his opinion : " This 



