420 ATMOSPHERIC EXPERIMENTS. 



under its influence. I endeavoured to ascertain 

 the power of absorption possessed by the air at the 

 time by an experiment, rude enough, to be sure, 

 yet it tended in some measure to indicate the rapid 

 manner in which fluids are exhaled in particular 

 states of the atmosphere. A linen cloth twelve 

 inches square, which had absorbed an ounce avoir- 

 dupois of water, was suspended in the shade in a 

 free current of air, and in the course of ten mi- 

 nutes it had lost 436 grains, equal to one- sixteenth 

 of its weight. This great evaporation was princi- 

 pally effected by the absorbent power of the air, 

 and manifested in some degree the exhausting in- 

 fluence that was passing over the earth and the 

 vegetation exposed to the current of air ; and as 

 the roots could not derive sufficient moisture from 

 the soil to supply what was thus drawn from the 

 leaves, the foliage became languid and flaccid in 

 consequence. The linen, containing the same 

 quantity of water, was then spread upon a short 

 turf in the sun, and in the space of ten minutes it 

 lost 368 grains, and this was effected without any 

 particular influencing current of air ; accordingly, 

 the evaporation from an acre of moist land covered 

 with vegetation would exceed one hundred and 

 twenty-two cwt. of water in an hour ! As the 

 quantity drawn from the vegetation on the soil may 

 be equal to the shelter its foliage affords to the 

 earth, no very accurate data can be drawn from 

 this experiment ; for different soils will give out 

 tlieir moisture more or less easily, and succulent 



