ON DEW, &c. 143 



10 grains of wool, exposed to the air on the 

 outside of one of my chamber windows, to in- 

 crease, during a whole night, more than ^ a 

 grain in weight. When this weight was gained, 

 the weather was clear and still ; if the weather 

 was cloudy and windy, the wool received either 

 less or no weight. This window is so situated, 

 as to be, in great measure, deprived of the 

 aspect of the sky. 



It being shewn, that wool, though highly at- 

 tractive of dew, was prevented, by the mere 

 vicinity of a gravel walk, or a bed of garden 

 mould, for only a small part of it actually 

 touched those bodies, from acquiring nearly as 

 much dew, as an equal parcel laid upon grass, 

 it may be readily inferred, that little was formed 

 upon themselves. In confirmation of this con- 

 clusion, I shall mention, that I never saw dew 

 upon either of them. Another fact of the same 

 kind is, that, while returning to London from 

 the scene of my experiments about sunrise, I 

 never observed, if the atmosphere was clear, 

 the public road, or any stone pavement on the 

 side of it, to be moistened with dew, though 

 grass within a few feet of it, and painted doors 

 and windows of houses not far from it, were 

 frequently very wet. If, indeed, there was a 

 foggy morning, after a clear and calm night, 

 even the streets of London would sometimes be 



