ATMOSPHERIC EXPERIMENTS. 275 



with a calm deep-rooted conviction implanted in the 

 boy, and increased by years of notice and experience. 

 I have followed her footsteps, though far, very far dis- 

 tant, as an humble admirer of perfection, nor can my 

 veneration cease whilst reason continues undisturbed. 



Sept. 8th, 1828. A remarkably dry and exhausting 

 day, not from any peculiar influence of the solar heat, 

 but from the arid state of the air, which was very dis- 

 tressing to our feelings, and all tender vegetation be- 

 came languid and suffering under its influence. I en- 

 deavored 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 par- 

 ticular states of the atmosphere. A linen cloth twelve 

 inches square, which had absorbed an ounce avoirdu- 

 pois of water, was suspended in the shade in a free 

 current of air, and in the course of ten minutes it had 

 lost 436 grains, equal to one-sixteenth of its weight. 

 This great evaporation was principally effected by the 

 absorbent power of the air, and manifested in some de- 

 gree the exhausting influence 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 conse- 

 quence. 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 ex- 

 ceed 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 their mois- 

 ture more or less easily, and succulent vegetables be 



