352 PHYSICAL GEOGRAPHY OF THE SEA. 



mence to move rapidly over tlie ocean, and down toward the 

 south, until the last of February or the first of March ; then again 

 they would become stationary, and remain about this, their south- 

 ern tropic, till May again. Having completed his physical exam- 

 ination 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 (§ 210), and another bordering the south- 

 east trade-winds on the south (§ 213). These calm zones also 

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

 zones, partaking (§ 296) of their motions, and following the decli- 

 nation of the sun. 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 

 i n 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 (§ 210) the wind blows perpetually to- 

 ward the equator ; on the other, its prevailing direction is toward 

 the poles. They are called (§ 210) the " horse latitudes" by seamen. 



655. Along the polar borders of these two calm belts (§ 296) 

 Rainy seasons of the ^6 havc auothcr rcgiou of prccipitatiou, though 

 tropical calm belts, 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 when- 

 ever these calm zones, as they go from north to south with the 

 sun, leave a given parallel, the rainy season 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 California at the north. 



656. We can now imderstand why the calm belts of Cancer 

 Their position, and Capricom occupy a medial position between 



the trades and the counter-trades ; why, on one side of it, the pre- 

 vailing direction of the wind should be polarward, on the other 

 toward the equator; and we also discover the influences which 

 determine their geographical position. 



657. An accumulation of atmosphere over one part of the earth's 

 A meteorological law. surfacc implies a deprcssioii over some other part, 

 precisely as the piling up of water into a wave above the sea lev- 

 el involves a corresponding dopression below ; and in meteorol- 



