130 ESSAY 



in the afternoon, and sunset. Contrary, how- 

 ever, to what happens at sunset, if the weather 

 be favourable, more dew forms a little before, 

 and, in shaded places, a little after sunrise, than 

 at any other time. Musschenbroek, therefore, 

 errs greatly when he says, that dew does not 

 form after the sun has risen. The preceding 

 observations, on the early appearance of dew in 

 the afternoon, are to be restricted to what hap- 

 pens to grass, or other substances highly attrac- 

 tive of dew placed on the ground ; for it occurs 

 much later on similar substances, which are 

 elevated a few feet above the ground, though 

 upon these it continues to form, as long after 

 the rising of the sun, as upon the others, if they 

 be equally sheltered from the rays of that body. 

 The formation of dew, after it has once com- 

 menced, continues during the whole night, if 

 the weather remain still and serene. Mr. 

 Prieur, indeed, of whom I have already spoken, 

 asserts, that dew forms only in the evening and 

 morning, and that any which occurs in the 

 former season always disappears in the course 

 of the night. I can affirm, however, from long 

 experience, that grass, after having been dewed 

 in the evening, is never found dry until after 

 sunrise, unless the weather has, in the mean 

 time, changed. Upon one serene and still 

 night, I placed fresh parcels of wool upon grass 



