ON DEW, &c. 149 



the course of the night ; and the same effect 

 was almost always observed, if the plate had 

 been placed horizontally in the air, a few inches 

 above the grass. While the undersides were 

 thus moist, the upper surfaces were very often 

 dry. If, however, the plate was elevated several 

 feet in the air, the condition of both sides was 

 always the same, whether this was dry or moist. 



The remarks hitherto made, on the relation 

 of metals to dew, apply to the class generally; 

 but it is now to be mentioned, that they do not 

 all resist the formation of that fluid, with the 

 same force. 



I saw, for example, platina one night dis- 

 tinctly dewed, while gold, silver, copper and 

 tin, though similarly situated, were entirely 

 dry ; and I have also several times seen these 

 four metals free from dew, while iron, steel, 

 zinc, and lead were covered with it. 



I once supposed, in consequence of the dif- 

 ficulty with which metals are dewed, that they 

 might in all circumstances resist, in a greater 

 degree than other bodies, the condensation of 

 watery vapour upon their surface ; and I after- 

 wards found, that Le Roi* asserts this to be 

 the case. But having exposed at the same time, 

 to the steam of warm water, pieces of glass and 



* Mem. de 1'Acad. Fran. 1751. 



