ON DEW, &c. 241 



frost appears, when the surface of the earth is 

 sealed with frost, and of course the vapour of 

 which it is formed, cannot at the time, perspire 

 from the earth." 



3. I have myself, at all seasons of the year, 

 frequently observed wool, upon the middle of 

 the raised board, and therefore out of the way 

 of vapour rising from the ground, to acquire 

 more dew, than wool laid upon the grassplat. 



4. The bodies, that condense the rising va- 

 pour, must necessarily be colder than it ; but, 

 as they are likewise, according to the opinion 

 under view, of the same temperature with the 

 air surrounding them, this also should condense 

 the rising vapour. Dew, therefore, should never 

 appear in any considerable quantity, without 

 being accompanied with fog or mist. Now I 

 can assert after much attention to this point, 

 that the formation of the most abundant dew 

 is consistent with a pellucid state of the atmo- 

 sphere. Hasselquist makes a similar observa- 

 tion, with regard to Egypt j where, during the 

 season remarkable for the most profuse dews, 

 " the nights," he says, " are as resplendent with 

 stars, in the midst of summer, as the lightest 

 and clearest winter nights in the north." 



But, although these facts prove, that copious 

 dews may occur with little or no contribution 

 by vapour immediately rising from the earth, it 



