124 The Realm of Nature CHAP. 



prevailing winds by plateau edges and mountain ranges. 

 Regular zones of surface winds and climates consequently 

 are found only in great expanses of ocean, and do not 

 appear in narrow seas or on land (see Plates V. VI. VII.) 



179. Trade Winds and Doldrums. When the Spanish 

 and Portuguese explorers of the i6th century found that 

 north-easterly winds blew steadily all the year round on 

 the Atlantic between 30 and 5 N. and enabled them 

 to make quick voyages to the West Indies, they gave 

 the name of Trade Winds to the favouring breezes. The 

 name has since been extended to include all the permanent 

 winds which blow from the tropical toward the equatorial 

 calms. In the winter half of the year (November to April) 

 the north-east trades of the Atlantic are felt as far north as 

 25 N. and reach southward to 5 N. ; and in the Pacific 

 they sweep over the range of sea between 28 N. and 8 N., 

 and the tropical calms reach as far north as 40. The 

 south-east trade winds at the same season are experienced 

 in the Atlantic between a line drawn from the Cape of 

 Good Hope to Rio de Janeiro, and the equator. In the 

 eastern Pacific they reach farther north, crossing the equator 

 to at least 5 N. The equatorial belt of calms and rains 

 lies entirely to the north of the equator ; its width varies 

 from 1 20 to 200 miles in the Atlantic, and is about 300 

 miles in the Pacific. This calm belt, called by sailors the 

 Doldrums, was greatly dreaded in the days of sailing 

 ships, on account of the absence of wind, which often kept 

 a vessel rolling helplessly for weeks, while the close damp 

 air made the men dispirited and ill. Thunderstorms of 

 terrific violence are very common in it. It was consequently 

 of the greatest importance for a captain to know where the 

 narrowest part of the belt could be found at each season, in 

 order that he might pass quickly from the clea^r bright skies 

 and fresh invigorating winds of the north-east trades to the 

 equally pleasant and favourable region of the south-east 

 trades. During the summer half-year (May to October) 

 the rain-belt of the Doldrums with its calms moves farther 

 north, and widens to from 300 to 500 miles. The north- 

 east trades then begin in about 30 N. and die off about 



