294 THE CHEMISTRY OF CREATION. 



not in solution. Dust comes down with the 

 purest rain, consisting chiefly of coal-ashes, 

 which is apparently the source of the sulphates 

 and chlorides found in rain. It is sometimes 

 acid with sulphuric acid. 



Though, doubtless, the presence of these 

 matters in the atmosphere is in a lesser degree 

 injurious to human respiration, it is far more so 

 to vegetable life ; for neither the most healthy 

 previous condition, nor the most careful tending, 

 will preserve plants in health in our large cities. 

 It appears, therefore, that we have a cause of 

 thankfulness, at least in some respects, even for 

 the proverbial fickleness of our climate, since its 

 copious showers are the appointed means for 

 counteracting that measure of mischief which 

 might otherwise arise. 



Let us follow the rain-drops in their descent 

 into the earth. Whatever soluble matter is met 

 with by the rain at the surface of the soil, it 

 carries with it as it sinks downward into the 

 earth. All the unpleasant results of organic 

 decay on the surface that are soluble, are con- 

 veyed downwards by it, and the water, thus pol- 

 luted, sinks to the underground reservoirs, from 

 whence man draws his supply of this indispen- 

 sable fluid. What results might we not therefore 

 anticipate on an examination of water drawn 

 from such receptacles; and what a polluted 



