98 THE PHYSICAL GEOGRAPHY OF THE SEA. 



these rivers; and the quantity discharged annually by each river 

 is, as far we can judge, nearly a constant. 



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

 Powerful machineiy. atmosphcrc Hiust be; and, though it is apparently 

 so capricious and wayward in its movements, here is evidence of 

 order and arrangement which we must admit, and proof which we 

 can not deny, that it performs this mighty office with regularity 

 and certainty, and is therefore as obedient to law as is the steam- 

 engine to the will of its builder. It, too, is an engine. The South 

 Seas themselves, in all their vast intertropical extent, are the 

 boiler for it, and the northern hemisphere is its condenser (§ 24). 

 The mechanical power exerted by the air and the sun in lifting- 

 water from the earth, in transporting it from one place to another, 

 and in letting it down again, is inconceivably great. The utilita- 

 rian who compares the water-power that the Falls of Niagara 

 would afford if applied to machinerj^, 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 horses. 



