228 ESSAY 



of the very tops of trees are fully exposed to the 

 sky. 5. The declension of the leaves fron* an 

 horizontal position will occasion the air, which 

 has been cooled by them, to slide quickly away, 

 and be succeeded by warmer parcels. 6. The 

 length of the branches of the trees, the tender- 

 ness of their twigs, and the pliancy of the foot- 

 stalks of their leaves, will cause in the leaves an 

 almost perpetual motion, even in states of air 

 that may be denominated calm. I have hence 

 frequently heard, during the stillness of night, 

 a rustling noise in the trees, which formed one 

 of the boundaries of the ordinary place of my 

 observations, while the air below seemed with- 

 out motion. 



Nearly in the same manner is to be ex- 

 plained, why shrubs and bushes also receive 

 dew more readily than lofty trees. 



X. Bright metals, exposed to a clear sky in a 

 calm night, will be less dewed on their upper 

 surface than other solid bodies ; since of all 

 bodies they will, in such a situation, lose the 

 smallest quantity of heat by radiation to the 

 heavens, at the same time that they are capable 

 of receiving, by conduction, at least as much 

 heat as any others from the atmosphere, and 

 more than any others from the warmer solid 

 substances, which they happen to touch. 



If the exposed pieces of metal be not very 



