228 THE PHYSICAL GEOGRAPHY OF THE SEA. 



those seas would have been lessened if a snow-capped range of 

 mountains (§ 620) had been elevated across the path of these 

 winds, between the places where they were supplied with vapor 

 and these basins. 



635. A chain of evidence which it would be difficult to set 

 aside is contained in the chapters begmning severally at p. 70, 125, 

 and 209, going to show that the vapor which supplies the extra- 

 tropical regions of the north with rains comes, in all probability, 

 from the trade-wind regions of the southern hemisphere. 



636. Now if it be true that the trade- winds from that part of 

 the world take up there the water which is to be rained in the 

 extra-tropical north, the path ascril^ed to the southeast trades of 

 Africa and America, after they descend and become the prevailing 

 southwest winds of the northern hemisphere, should pass over a 

 region of less precipitation generally than they would do if, while 

 performing the office of southeast trades, they had blown over wa- 

 ter instead of land. The southeast trade-winds, with their load 

 of vapor, whether great or small, take, after ascending in the equa- 

 torial calms, a northeasterly direction ; they continue to flow in- 

 the upper regions of the air in that direction until they cross the 

 tropic of Cancer. Tlie places of least rain, then, between this 

 tropic and the pole, should be precisely those places which depend 

 for their rains upon the vapor which the winds that blow over 

 southeast trade-wind Africa and America convey. 



637. Now, if we could trace the path of the winds through the 

 extra-tropical regions of the northern hemisphere, we should be 

 able to identify the track of these Andean winds by the foot-prints 

 of the clouds ; for the path of the winds which depend for their 

 moisture upon such sources of supply as the dry land of Central 

 South America and Africa can not lie through a country that is 

 watered well. 



638. It is a remarkable coincidence, at least, that the countries 

 in the extra-tropical regions of the north tliat are situated to the 

 northeast of the southeast trade-winds of South Africa and Amer- 

 ica — that these countries, over which theory makes these winds 

 to blow, include all the great deserts of Asia, and the districts of 

 least precipitation in Europe. A line from the Galapagos Islands 



