THE WINDS. 291 



the first of March ; then again they would "become stationary, and 

 remain about this, tlieir southern tropic, till May again. 



840. The Hoese Latitudes. — Having completed the physical 

 examination of the equatorial calms and winds, if the supposed ob- 

 server should now turn his telescope toward the poles of our earth, 

 he would observe a zone of calms bordering the northeast trade- 

 winds on the north (§ 131), and another bordering the southeast 

 trade-winds on the south (§ 137). These calm zones also would 

 be observed to vibrate up and down with the trade-wind zones, 

 partaking (§ 191) of their motions, and following the decHnation 

 of the sun. 



841. On the polar side of each of these two calm zones there 

 would be a broad band extending up into the polar regions, the 

 prevailing winds within which are the opposites of the trade-winds, 

 viz., southwest in the northern and northwest in the southern 

 hemisphere. The equatorial edge of these calm belts is near the 

 tropics, and their average breadth is 10° or 12^. On one side of 

 these belts (§ 131) the winds blow perpetually toward the equator ; 

 on the other, their prevailing direction is toward the poles. They 

 are called (§ 131) the "horse latitudes" by seamen. 



842. Along the polar borders of these two calm belts (§ 190) 

 we have another region of precipitation, though generally the rains 

 here are not so constant as they are in the equatorial calms. The 

 precipitation near the tropical calms is nevertheless sufficient to 

 mark the seasons ; for whenever these calm zones, as they go from 

 north to south with the sun, leave a given parallel, the rainy sea- 

 son of that parallel, if it be in winter, is said to commence. Hence 

 we may explain the rainy season in Chili at the south, and in Cal- 

 ifornia at the north. 



843. The Westerly Winds. — To complete the physical ex- 

 amination of the earth's atmosphere which we have supposed an 

 astronomer in one of the planets to have undertaken according to 

 the facts developed by the Wind and Current Charts, it remains 

 for him to turn his telescope upon the southwest passage winds of 

 the northern hemisphere, pursue them into the arctic regions, and 

 see theoretically how they get there, and, being there, what be- 

 comes of them. 



844. From the parallel of 40° up toward the north pole, the 



T 



