THE TRADE WIXDS. 



beyond the equatorial line. Their character is that of a con- 

 tinual soft breeze — strongest in the morning, remitting at noon, 

 and again increasing in the evening. In the neighbourhood of 

 the coasts, except over very small islands, they become weaker, 

 and generally cease to be felt at a distance of about fifteen or 

 twenty miles from the sea, though, of course, at greater heights 

 they continue their course uninterruptedly over the land. 



For obvious reasons the trade winds have been much more 

 accurately investigated upon the ocean than on land, particularly 

 in the Northern Atlantic, which is better known in its physical 

 features than any other sea, as being a highway for numberless 

 vessels to which the study of the winds is a matter of the greatest 

 importance ; yet, in spite of so many disturbing influences, their 

 course, even over the continents, has been ascertained by tra- 

 vellers. North-easterly winds almost constantly sweep over the 

 Sahara ; and in South Africa, Dr. Livingstone informs us that 

 north-easterly and south-easterly winds blow over the whole 

 continent between 12° and 6° S. lat,, even as far as Angola, 

 where they unite with the sea winds* 



In Brazil, the presence of the trade winds has been determined 

 with still greater accuracy. Thus easterly breezes almost per- 

 petually sweep over the boundless plains up to the slopes of the 

 Andes, and even in Paraguay (25° S. lat.) a mild east wind 

 constantly arises in summer after the setting of the sun. 



As the trade winds originate in the coldest, and thence pass 

 onwards to the warmer regions, they are, of course, constantly 

 absorbing moisture as they advance over the seas. Saturated 

 with vapours, they reach the islands and continents, where, 

 meeting with various refrigerating influences (mountain-chains, 

 forests, terrestrial radiation), their condensing vapours give rise 

 to an abundance both of rain and dew. It is owing to their 

 influence that in general, within the tropics, the eastern coasts, 

 or the eastern slopes of the mountains, are better watered than 

 the interior of the continents or lands with a western exposure. 



An example on the grandest scale is afforded to us by South 

 America, where the Andes of Peru and Bolivia so effectually 

 drain the prevailing east winds of their moisture, that while 

 numberless rivulets, the feeders of the gigantic Maraiion, clothe 

 their eastern gorges with a perpetual verdure, their western 

 slopes are almost constantly arid. Such is the influence of this 



