SEA ROUTES, CALM BELTS, AND VARIABLE WINDS. 353 



changes from day to day are very great. He would observe that 

 the zones of winds and cahiis have their tropics or stationary 

 nodes, about w^hich they linger near three months at a time ; and 

 that they pass from one of their tropics to the other in a little less 

 than another three months. Thus he would observe the whole 

 system of belts to go north from the latter part of May till some 

 time in August. Then they would stop and remain nearly sta- 

 tionary till winter, in December ; when again they would com- 

 mence to move rapidly over the ocean, and down towards the 

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

 they would become stationary, and remain about this, their 

 southern tropic, till May again. Having completed his physical 

 examination of the equatorial calms and winds, if the supposed 

 observer should now turn his telescope towards the poles of our 

 «arth, he w^ould observe a zone of calms bordering the north-east 

 trade-w^inds 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 

 declination 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 wands wdthin which are the oppo- 

 sites of the trade-winds, viz., south-west in the northern and 

 north-west 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 (§ 210) the wind blows 

 perpetually towards the equator ; on the other, its prevailing 

 direction is towards the poles. They are called (§ 210) the 

 " horse latitudes " by seamen. 



655. Hainy seasons of the tropical calm belts. — Along the polar 

 borders of these two calm belts (§ 296) 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 sujBicient 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 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. Their position. — AYe can now understand why the calm 

 belts of Cancer and Capricorn occupy a medial position between 



2 A 



