TRADE-WI^DS. 215 



same kind as that presented on a far smaller scale 

 by the land and sea breezes. 



In the torrid zone, then, we find in the lower 

 layers of the atmosphere, on both sides of the 

 equator, polar winds — blowing from the poles to 

 the equator — north winds in the northern hemi- 

 sphere, and south winds in the southern, both of 

 which, however, for a reason winch I shall pre- 

 sently explain, take a more and more westward 

 direction as they approach the equator. These 

 are called the Trade-winds. 



In the higher layers of the atmosphere, equatorial 

 winds prevail, — winds whose general direction is 

 from the equator to the poles, — winch however take 

 a more and more westerly direction as they pro- 

 gress. These are called the Upper or Returning 

 Trade-winds. 



Where the lower trade- winds of the northern and 

 southern hemispheres meet, a region lies, in which 

 there blows only a slight east wind, which, however, 

 often lulls altogether, and is sometimes changed 

 for the most violent storms. This is the Region 

 of Calms so much dreaded by sailors. In this 

 belt, the hottest of the earth, the currents of air 

 that flow from the poles, becoming continually 

 warmer, do not come down lower than at least 

 twenty thousand feet above the surface, for no tra- 

 veller even on the highest peaks of the Andes lias 

 ever got into the upper trade-wind. However, 



