§ 276, 277. RAINS AND RIVERS. 108 



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 preserve 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 surplus- 

 age of heat, which could not otherwise be got rid of without first 

 disturbing the terrestrial arrangements, and producing on the land 

 desolation and a desert. Behold now the of&ces of clouds and 

 vapor — the adaptations of heat. Clouds and vapor do something 

 more than brew storms, fetch rain, and send down thunder-bolts. 

 The benignant vapors cool our climates in summer by rendering 

 latent the excessive heat of the noonday sun ; and they temper 

 them in winter, by rendering sensible and restoring again to the 

 air the equivalent of that selfsame heat. 



276. Whence came, and by what channels did they come, these 

 Whence come the cubic milcs of watcr whicli the Mississippi River 



rains for the Missis- t i • i o 



sippi- pours annually into the sea ? The wisest of men 



has told us they come from the sea. Let us explore the sea for 

 their place and the air for their channel. The Gulf of Mexico 

 can not furnish rain for all the Mississippi Yalley. The Gulf lies 

 within the region of the northeast trades, and these winds carry 

 its vapors off to the westward, and deliver them in rain to the 

 hills, and the valleys, and the rivers of Mexico and Central Amer- 

 ica. The winds that bring the rains for the upper Mississippi 

 Valley come not from the south ; they come from the direction of 

 the Rocky 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 ex- 

 amine the Atlantic Ocean, and include its slopes also in the inves- 

 tigation. 



277. The northeast trade-wind region of this ocean extends 

 Thenortheast trades (S 210) from the parallel of 80° to the eq uator. They 



of the Atlantic sup- ,. in i -i t* 



ply rains only for the carrv their vapor bcforc them, and, meeting the 



rivers of Central and "l •^. pit i-i- 



South America. southcast tradc-wiud, the two form clouds which give 

 rain not only to Central America, but they drop down, also, water 

 in abundance for the Atrato, the Magdalena, the Orinoco, the Am- 

 azon, and all the great rivers of intertropical America ; also for the 

 Senegal, the Niger, and the Congo of Africa. So completely is the 



