ON DEW, &c. 141 



abundant formation of dew, that the substance 

 attracting it should rest on a stable horizontal 

 body of some extent. Thus, upon one night, 

 while 10 grains of wool, laid upon the raised 

 board, increased 20 grains in weight, an equal 

 quantity, suspended in the open air, 5j feet 

 above the ground, increased only 1 1 grains, 

 notwithstanding that it presented a greater sur- 

 face to the air than the other parcel. On an- 

 other night, 10 grains of wool gained on the 

 raised board 19 grains, but the same quantity 

 suspended in the air, on a level with the board, 

 only 13; and on a third, 10 grains of wool ac- 

 quired, on the same board, 2 J grains of weight, 

 during the time in which other 10 grains, hung 

 in the air, at the same height, acquired only \ 

 a grain. 



In the second place ; the quantities of dew 

 attracted by equal masses of wool, similarly ex- 

 posed to the sky, and resting on equally stable 

 and extended bodies, oftentimes vary consider- 

 ably, in consequence of some difference in the 

 other circumstances of these bodies. 10 grains 

 of wool, for instance, having been placed upon 

 the grassplat, on a dewy evening, 10 grains 

 upon a gravel walk which bounded the grass- 

 plat, and 10 grains upon a bed of bare garden 

 mould, immediately adjoining the gravel walk; 

 in the morning, the wool on the grass was 



