RAINS AND KIVEKS. 109 



are the sources of man's meclianical powers when compared 

 with those employed by nature in moving machinery Avhich 

 brings the seasons round and preserves the harmonies of creation ! 



275. Physical adaptations. — The amount of heat required to 

 reconvert these 513 cubic miles of rain-water into vapour and 

 bear it away, had accumulated in the Mississippi Valley faster 

 than the earth could throw it off by radiation. Its continuance 

 there would have been inconsistent with the terrestrial economy. 

 From this stand-point we see how the rain-drop is made to pre- 

 serve the harmonies of nature, and how water from the sea is 

 made to carry off by re- evaporation from the plains and valleys 

 of the earth their surplusage of heat, which could not otherwise 

 be got rid of without first disturbing the terrestrial arrange- 

 ments, and producing on the land desolation and a desert. Be- 

 hold now the offices of clouds and vapour — the adajDtations of 

 heat. Clouds and vapour do something more than brew storms, 

 fetch rain, and send down thunder-bolts. The benignant vapours 

 cool our climates in summer by rendering latent the excessive 

 heat of the noondaj^ sun ; and they temper them in winter by ren- 

 dering sensible and restoring again to the air, that self-same heat. 



276. Whence come the rains for the Mississijpjpi. — Whence came, 

 and by what channels did they come, these cubic miles of water 

 which the Mississippi River pours annually into the sea ? The 

 wisest of men has told us they come from the sea. Let us ex 

 plore the sea for their place and the air for their channel. The 

 Gulf of Mexico cannot furnish rain for all the Mississippi Valley. 

 The Gulf lies within the region of the north-east trades, and 

 these winds carry its vapours off to the westward, and deliver 

 them in rain to the hills, and the valleys, and the rivers of 

 Mexico and Central America. The winds that bring the rains 

 for the upper Mississippi Valley come not from the south ; they 

 come from the direction of the Eocky Mountains, the Sierra 

 Nevada, and the great chain that skirts the Pacific coast. It is, 

 therefore, needless to search in the Gulf, for the rain that comes 

 from it upon that valley is by no means sufficient to feed one 

 half of its springs. Let us next examine the Atlantic Ocean, 

 and include its slopes also in the investigation. 



277. Tlie north-east trades of the Atlantic supply rains only for the 

 rivers of Central and South America.— The north-east trade-wind 

 region of this ocean extends (§ 210) from the parallel of 30'^ In 

 the equator. These winds carry their vapour before them, and, 



