THE FACTORS OF DISTRIBUTION 41 



moisture and rain. Winds are dependent upon dif- 

 ferences of atmospheric pressure; and we recognise 

 seven irregular belts of climate, characterised by their 

 winds, and dependent upon the existence of an equatorial 

 belt of heated, moist, upward-tending air and consequent 

 low pressure, flanked by two belts of high pressure in 

 about latitudes 23 35. Apart from the great local 

 irregularity of the Asiatic monsoons, these belts are: 



v i. The Equatorial Belt of calms and variable winds 

 and constant precipitation, known nautically as the 

 Doldrums, with sultry, often thunderous, humid air 

 and little seasonal variation, extending from 3 to n 

 north of the Equator. 



2 and 3. The North and South Intermediate or Trade- 

 Wind Belts, so called by the Spaniards and Portuguese 

 of the sixteenth century from the utility of the N.E. 

 wind in making the voyage to the West Indies. These 

 areas extend between 3 and 35 north and south of the 

 Equator, and are characterised by the constant N.E. 

 and E. winds in the Northern, and S.E. and E. in the 

 Southern Hemisphere, with dry air and small rainfall, 

 since the wind is constantly moving from colder to 

 warmer latitudes, and cannot pick up moisture fast 

 enough to maintain saturation. 



4 and 5. The North and South High -Pressure Belts, 

 the Calms and Variables of Cancer and Capricorn, or 

 Horse Latitudes, somewhat poleward from either tropic, 

 with very hot, dry air and strong winds. 



6 and 7. The Higher North and South Latitudes, or 

 Anti-Trades ; the Northern with " Westerly Variables," 

 or South-westerly wind ; the Southern Belt, that of the 

 Brave West Winds, N.W. and W., between 40 and 50 

 S. lat., as regular as the Trade- winds and stronger. The 

 chief rainfall in these belts is associated with the great 

 atmospheric eddies known as cyclones, which are most 

 frequent in winter. 



The position of these belts changes with the season. 

 The equatorial belt of low pressure always lies nearly 

 under the vertical sun; and, consequently, in the 

 northern summer it swings to the north, and in the 

 southern summer to the south, displacing the tropical 

 high -pressure belts alternately northward and south- 

 ward. Thus all parts of the earth's surface traversed 

 by this equatorial rain-belt in its annual movement have 



