298 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



North America, in the latitude of the Caspian Sea, is our great 

 s^'stem of fresh- water lakes ; all of these receive from the 

 atmosphere immense volumes of water, and pour it back into 

 the sea in streams the most majestic. It is remarkable that none 

 of these copiously-supplied water-sheds have to the south-west 

 of them, in the trade-wind regions of the southern hemisphere, 

 any considerable body of land ; they are, all of them, under the 

 lee of evaporating surfaces in the trade-wind regions of the 

 south. Only those countries in the extra-tropical north which 

 I have described as lying under the lee of trade-wind South 

 America and Africa are scantily supplied with rains. Pray 

 examine Plate VII. in this connection. It tends to confirm the 

 views taken in Chapter YII. The surface of the Caspian Sea is 

 about equal to that of our lakes ; in it, evaporation is just equal 

 to the precipitation. Our lakes are between the same parallels, 

 and about the same distance from the western coast of America 

 that the Caspian Sea is from the western coast of Europe ; and 

 yet the waters discharged by the St. Lawrence give us an idea of 

 how greatly the precipitation upon its hydrographic basin is in 

 excess of the evaporation. To windward of the lakes, and in the 

 trade-wind regions of the southern hemisphere, is no land ; but 

 to windward of the Caspian Sea, and in the trade-wind region of 

 the southern hemisphere, there is land. Therefore, supposing 

 the course of the vapour-distributing winds to be such as I 

 maintain it to be, ought they not to carry more water from 

 the ocean to the American lakes than it is possible for them 

 to carry from the land — from the interior of South Africa and 

 America — to the valley of the Caspian Sea? In like manner 

 (§ 365), extra-tropical New Holland and South Africa have each 

 land — not water — to the windward of them in the trade- wind 

 regions of the northern hemisphere, where, according to this 

 hypothesis, the vapour for their rains ought to be taken up : 

 they are both countries of little rain ; but extra-tropical South 

 America has, in the trade-wind region to windward of it in the 

 northern hemisphere, a great extent of ocean, and the amount 

 of precipitation (§ 299) in extra-tropical South America is 

 wonderful. The coincidence, therefore, is remarkable, that the 

 countries in the extra-tropical regions of this hemisphere, which 

 lie to the north-east of large districts of land in the trade-wind 

 regions of the other hemisphere, should be scantily supplied with 

 rains ; and likewise that those so situated in the extra-tropical 



