86 THE PHYSICAL GEOGRAPHY OF THE SEA. 



rains of heaven, and these rains are formed of vapors which are 

 taken up from the sea, that " it he not full," and carried up to the 

 mountains through the air. 



"Note the place whence the rivers come, thither they return 

 again." 



166. Behold how the waters of the Amazon, of the Mississippi, 

 the St. Lawrence, and all the great rivers of America, Europe, and 

 Asia, lifted up by the atmosphere, and flowing in invisible streams 

 back through the air to their sources among the hills (§ 112), and 

 that through channels so regular, certain, and well defined, that 

 the quantity thus conveyed one year with the other is nearly the 

 same : for that is the quantity which we see running down to the 

 ocean through these rivers ; and the quantity discharged annually 

 by each river is, as far as we can judge, nearly a constant. 



167. We now begin to conceive what a powerful machine the 

 atmosphere must be ; and, though it is apparently so capricious 

 and wayward in its movements, here is evidence of order and ar- 

 rangement which we must admit, and proof which we can not 

 deny, that it performs this mighty office with regularity and cer- 

 tainty, and is therefore as obedient to law as is the steam-engine 

 to the will of its builder. 



168. It, too, is an engine. The South Seas themselves, in all 

 their vast inter-tropical extent, are the boiler for it, and the north- 

 ern hemisphere is its condenser. The mechanical power exerted 

 by the air and the sun in lifting water from the earth, in trans- 

 porting it from one place to another, and in letting it down again, 

 is inconceivably great. The utilitarian who compares the water- 

 power that the Falls of Niagara would afford if applied to ma- 

 chinery, is astonished at the number of figures which are required 

 to express its equivalent in horse-power. Yet what is the horse- 

 power of the Niagara, falling a few steps, in comparison with the 

 horse-power that is required to lift up as high as the clouds and 

 let down again all the water that is discharged into the sea, not 

 only by this river, but by all the other rivers in the world. The 

 calculation has been made by engineers, and, according to it, the 

 force for making and lifting vapor from each area of one acre that 

 is included on the surface of the earth is equal to the power of 30 



