ON DEW, &c. 147 



small plate will resist the formation of dew 

 more powerfully than the large. 



If a metal be closely attached to a substance 

 of some thickness, which attracts dew power- 

 fully, the attraction of the metal itself for dew, 

 instead of being increased from this circum- 

 stance, becomes diminished, provided the metal 

 cover the whole of the upper surface of the 

 other body. If only a part of this body be co- 

 vered, the production of dew on the metal is 

 forwarded by the conjunction, and this some- 

 what in proportion, to the quantity of surface 

 in the lower body left uncovered. The justness 

 of the first of these observations is proved by 

 the following experiment. I joined, in the 

 form of a cross, two pieces of very light wood, 

 each 4 inches long, a third of an inch in 

 breadth, and 1 line in thickness. To one side 

 of this cross I fastened, by means of mucilage, 

 a square piece of gilt paper, and then exposed 

 the instrument to the sky, with its metallic side 

 uppermost, on a dewy night, by suspending it, 

 in a horizontal position, about 6 inches above 

 the ground. A few hours after, the unattached 

 parts of the metalled paper were found covered 

 with minute drops of dew, while those, which 

 adhered to the cross, were dry. 



A large metallic plate, laid upon grass, was 

 dewed with more difficulty on its upper surface, 



*L 2 



