§290. RAINS AND KIVERS. m 



the macliinerj of the two hemispheres ? Are they not adapted to 

 each other ? Or, in studying the physical geography of our planet, 

 shall we regard the two hemispheres as separated from each other ? 

 Rather let us regard them as made for each other, as adapted to 

 each other, and the one as an essential to the other. So regard- 

 ing them, we observe that all the great rivers in the world are in 

 the northern hemisphere, where there is less ocean to supply them. 

 Whence, then, are their sources replenished ? Those of the Ama- 

 zon are, as we have seen (§ 277), supplied with rain from the equa- 

 torial calms and trade-winds of the Atlantic. That river runs east, 

 its branches come from the north and south ; it is always the rainy 

 season on one side or the other of it ; consequently, it is a river 

 without periodic stages of a very marked character. It is always 

 near its high-water mark. For one half of the year its northern 

 tributaries are flooded, and its southern for the other half. It dis- 

 charges under the line, and as its tributaries come from both hem- 

 ispheres, it can not be said to belong exclusively to either. It is 

 supplied with water made of vapor that is taken up from the At- 

 lantic Ocean. Taking the Amazon, therefore, out of the count, 

 the Rio de la Plata is the only great river of the southern hemi- 

 sphere. There is no large river in New Holland. The South Sea 

 Islands give rise to none, nor is there one in South Africa entitled 

 to be called great that we know of. 



290. The great rivers of North America and North Africa, and 

 Arguments furnished ^^^ ^hc rivcrs of Europc and Asia, lie wholly within 

 by the livers. ^^^ northcm hemisphere. How is it, then, consid- 



ering that the evaporating surface lies mainly in the southern hem- 

 isphere — how is it, I say, that we should have the evaporation to 

 take place in one hemisphere and the condensation in the other? 

 The total amount of rain which falls in the northern hemisphere 

 is much greater, meteorologists tell us, than that which falls in the 

 southern. The annual amount of rain in the north temperate 

 zone is half as much again as that of the south temperate. How 

 is it, then, that this vapor gets, as stated, from the southern into 

 the northern hemisphere, and comes with such regularity that our 

 rivers never go dry and our springs fail not ? It is because of 

 these air-crossings — these beautiful operations, and the exquisite 

 compensation of this grand machine, the atmosphere. It is ex- 

 quisitely and wonderfully counterpoised. Late in the autumn of 



