220 WINDS. 



slower rate ; and must, therefore, the farther they 

 get from the place of their origin, more and more 

 outrun the ground in its motion from west to east. 

 Hence, wherever these winds are met with, they 

 seem to blow from the westerly points of the com- 

 pass. 



Thus, in the northern hemisphere, a southerly 

 wind always becomes in its progress, first, a south- 

 west, and at last, a westerly current. 



In the southern hemisphere a northerly wind 

 passes gradually through a north-west into a west 

 wind. 



This explains why between the tropics an east 

 wind, and why in higher latitudes, especially 

 where the return trade-wind has fallen to the sur- 

 face, west winds are always prevalent, although 

 the former set out at first as polar, and the latter 

 as equatorial currents. These west winds, sinoe 

 they arise in the upper regions, where they can 

 meet with but very little resistance, have therefore 

 commonly a much greater speed than the east 

 winds, which are met with only in the lower layers 

 of the air. 



The trade- winds of the Atlantic Ocean are the 

 most thoroughly known by sailors. They extend 

 on both sides of the equator, several degrees be- 

 yond the tropics. The north-east trade-wind 

 blows between 9° and 27° north latitude; how- 

 ever, its northern, as well as its southern, limit 



