104 PHYSICAL GEOGBAPHY OF THE SEA, AND ITS METEOROLOGY. 



passes by in the Mississippi to be 93 cubic miles. The water 

 required to cover to the depth of 40 inches an area of 982,000- 

 square miles would, if collected together in one place, make a sea 

 one mile deep, with a superficial area of 620 square miles. 



274. It is estimated that the tributaries which the Mississippi 

 Anmiai discharge of Rivcr receivos below Memphis increase the volume 

 the Mississippi River. Qf ^j^^ watcrs about ouo eighth, so that its annual 

 average discharge into the sea may be estimated to be about 107 

 cubic miles, or about one sixth of all the rain that falls upon its 

 water-shed. This would leave 513 cubic miles of v>'ater to ba 

 evaporated from this river-basin annually. All the coal that the 

 present mining force of the country could raise from its coal 

 measm-es in a thousand years would not, during its combustion, 

 give out as much heat as is rendered latent annually m evaporating- 

 this water. Utterly insignificant are the sources of man's mechanical 

 powers when compared with those employed by nature in moving 

 machinery which brings the seasons round and preserves the- 

 harmonies of creation ! 



275. The amount of heat required to reconvert these 513 cubic 

 Physical adaptations, milcs of raiu- Water iuto vapour and bear it away, had 

 accumulated in the Mississippi Yalley 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 preserve the harmonies of 

 natm^e, and how water from the sea is made to carry off by re- 

 evaporation from the plains and valleys of the earth their sur- 

 plusage 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 offices of clouds and 

 vapom- — the adaptations of heat. Clouds and vapour do something 

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

 The benignant vapom'S 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, that selfsame heat. 



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

 Whence come the cubic milcs of watcr which the Mississippi Eiver 



rains for the Missis- n • j ji o rrn • l i- 



sippi, pours annually mto the sea f The wisest ot 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- 

 cannot fornish rain for all the Mississippi Yalley. The Gulf lies 



