232 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Eed Sea as a make-weiglit, thrown in to regulate the proportion 

 of cloud and sunshine, and to dispense rain to certain parts of the 

 earth in due season and in proper quantities ? Have we not, in 

 these two facts, evidence conclusive that the winds which blow over 

 these two seas come, for the most part, from a dry country — from 

 regions which contain few or no pools to furnish supplies of vapor? 



647. Indeed, so scantily supplied with vapor are the winds 

 which pass in the general channels of circulation over the water- 

 shed and sea-basin of the IMediterranean, that they take up there 

 more water as vapor than they deposit. But, throwing out of the 

 question what is taken up from the surface of the Mediterranean 

 itself, these winds deposit more water on the water-shed whose 

 drainage leads into that sea than they take up from it again. The 

 excess is to be found in the rivers which discharge themselves into 

 the Mediterranean ; but so thirsty are the winds w^hich blow across 

 the bosom of that sea, that they not only take up again all the 

 water that those rivers pour into it, but they are supposed by 

 philosophers to create a demand for an immense current from the 

 Atlantic to supply the waste. 



648. It is estimated that three* times as much water as the 

 Mediterranean receives from its rivers is evaporated from its sur- 

 face. This may be an over-estimate, but the fact that evapora- 

 tion from it is in excess of the precipitation, is made obvious by 

 the current which the Atlantic sends into it through the Straits 

 of Gibraltar ; and the difference, we may rest assured, whether it 

 be much or little, is carried off to modify climate elsewhere — to re- 

 fresh with showers and make fruitful some other parts of the earth. 



649. The great inland basin of Asia, in which are Aral and the 

 Caspian Seas, is situated on the route w^hich this hypothesis re- 

 qunes these thirsty winds from southeast trade-w^nd Africa and 

 America to take ; and so scant of vapor are these winds when 

 they arrive in tliis basin, that they have no moisture to leave be- 

 hind; just as much as they pour down they take up again and 

 carry off. We know (§ 166) that the volume of water returned 

 by the rivers, the rains, and the dews, into the whole ocean, is ex- 

 actly equal to the volume which the whole ocean gives back to 



* Vide article " Physical Geography," Encyclopsedia Britannica. 



