ON DEW, &c. 151 



upon one evening, 10 grains of wool gained 

 in it 3 grains of moisture, in 1 hour and 18 

 minutes, though I scarcely ever knew a greater 

 quantity to be collected by a similar parcel of 

 wool, in the same place, during a whole night. 

 These experiments will no doubt seem to many 

 superfluous, since dew may be observed every 

 fine evening, upon grass in London. But as 

 dew upon grass is said by Le Roi to proceed 

 from the ground, and not from the atmosphere, 

 the argument derived from its appearance there, 

 in cities, against his assertion is thus eluded by 

 him. 



The last subject, which I shall here touch 

 upon, is that of hoarfrost. 



This substance has, I believe, from the time 

 of Aristotle*, been uniformly, and, according 

 to my observations, justly, considered as frozen 

 dew. I shall, therefore, frequently refer here- 

 after to the experiments of the late Mr. Patrick 

 Wilson of Glasgow respecting it, as if they had 

 been actually made upon that fluid. Indeed, 

 several of my experiments upon dew were only 

 imitations of some, which had been previously 

 made upon hoarfrost, by that ingenious and 

 most worthy man. 



* Meteor. Lib. I. c, x. 



