144 ' ESSAY 



moist, though they had been dry the day before, 

 and no rain had in the meanwhile fallen. This 

 entire, or almost entire, freedom of certain si- 

 tuations from dew depends, however, much 

 more upon extraneous circumstances, than upon 

 the nature of the substances found there ; for 

 river sand, though of the same nature with 

 gravel, when placed upon the raised board, or 

 upon grass, attracted dew copiously. 



A third difference, from situation, in the 

 quantity of dew collected by similar bodies, 

 similarly exposed to the sky, depends upon 

 their position with respect to the ground. Thus, 

 a substance placed several feet above the 

 ground, though in this situation later dewed, 

 than if it touched the earth, would, notwith- 

 standing, if it lay upon a stable body of some 

 extent, such as the raised board lately men- 

 tioned, acquire more dew during a very still 

 night, than a similar substance lying on grass. 



A fourth difference of this kind occurred 

 among bodies placed on different parts of the 

 raised board. For one, that was placed at the 

 leeward end of it, generally acquired more dew 

 than a similar body at the windward extremity. 



II. Difference in the mechanical state of 

 bodies, though all other circumstances be similar, 

 has likewise an effect on the quantity of dew, 

 which they attract. Thus, more dew is formed 



