OF EVAPORATION, &C. 21 



Here, then, I come to the point necessary to eluci- 

 date the subject under consideration. When rain is 

 formed, it is by the simple condensation of the vapour 

 into drops. When hail is formed, it is first by con- 

 densation of the vapour into drops, which by a very 

 cold current are frozen into hail stones as they fall. 

 Snow is nothing more than half condensed vapour, fro- 

 zen just before it falls, by attraction, into drops. 

 Dew is fine vapour which has not ascended high into 

 the atmosphere, and falls before attraction renders 

 the drops large,, by bringing many of the particles 

 together. 



Now all these, by percolating or filtering through 

 the earth, leave the nitre which they contain in the 

 soil, and render it rich when the land is screened from 

 the sun by a coat of clover or any of the grasses. As 

 was observed before, this is effected in the same man- 

 ner that a spot of earth becomes rich when covered 

 with a plank or pile of stones. 



