212 THE ELEMENTS. 



Another general quality of the atmosphere is, the power 

 of evaporating fluids. The adjustment of this quality to 

 our use is seen in its action upon the sea. In the sea, 

 water and salt are mixed together most intimately ; yet 

 the atmosphere raises the water, and leaves the salt. Pure 

 and fresh as drops of rain descend, they are collected from 

 brine. If evaporation be solution, (which seems to be 

 probable,) then the air dissolves the water and not the salt. 

 Upon whatever it be founded, the distinction is critical ; so 

 much so, that, when v\e attempt to imitate the process by 

 art, we must regulate our distillation with great care and 

 nicety, or, together with the water, we get the bitterness, 

 or, at least, the distastefulness of the marine substance: 

 and, after all, it is owing to this original elective power in 

 the air, that we can effect the separation which we wi&h, 

 by any art or means whatever. 



By evaporation water is carried up into the air ; by the 

 converse of evaporation it falls down upon the earth. And 

 how does it fall ? Not by the clouds being all at once con- 

 verted into water, and descending like a sheet; not in 

 rushing down in columns from a spout; but in moderate 

 drops, as from a colander. Our watering-pots are made 

 to imitate showers of rain. Yet, d priori, I should have 

 thought either of the two former methods more likely to 

 have taken place than the last. 



By respiration, flame, putrefaction, air is rendered un- 

 fit for the support of animal life. By the constant oper^ 

 ation of these corrupting principles, the whole atmosphere, 

 if there were no restoring causes, would come at length 

 to be deprived of its necessary degree of purity. Some of 

 these causes seem to have been discovered, and their efii- 

 cacy ascertained by experiment. And so far as the dis- 

 covery has proceeded, it opens to us a beautiful and a 

 wonderful economy. Vegetation proves to be one of them, 

 A sprig of mint, corked up with a small portion of foul air 

 placed in the light, renders it again capable of supporting 

 life or flame. Here, therefore, is a constant circulation 

 of benefits maintained between the two great provinces of 

 organized nature. The plant purifies, what the animal 

 has poisoned : in return, the contaminated air is more than 

 ordinarily nutritious to the plant. Agitation with water 

 turns out to be another of these restoratives. The foulest 

 air, shaken in a bottle with water for a sufficient length of 

 time, recovers a great degree of its purity. Here then 

 again, allowing for the scale upon which nature works, we 



