268 THE PHYSICAL GEOGRAPHY OF THE SEA. 



east trade-winds. And as the northeast trade-winds blow under 

 the influence of a greater extent of land surface than the south- 

 east trades do, the former are more obstructed in their course than 

 the latter by the forests, the mountain ranges, unequally heated 

 surfaces, and other such like inequalities. 



766. As already stated, the investigations show that the mo- 

 mentum of the southeast trade-winds is sufficient to push the equa- 

 torial limits of their northern congeners back into the northern 

 hemisphere, and to keep them, at a mean, as far north as the ninth 

 parallel of north latitude. Besides this fact, they also indicate 

 that while the northeast trade-winds, so called, make an angle in 

 their general course of about 23° with the equator (east-north- 

 east), those of the southeast make an angle of 30° or more with 

 the equator (southeast by east) — I speak of those in the Atlantic — 

 thus indicating that the latter approach the equator more directly 

 in their course than do the others, and that, consequently, the ef- 

 fect of the diurnal rotation of the earth being the same for like 

 parallels, north and south, the calorific influence of the sun exerts 

 more power in giving motion to the southern than to the northern 

 system of Atlantic trade-winds : in other words, the southeast 

 trade-winds are, on the average, fresher than the northeast. 



767. The southeast trade-winds of the Atlantic, particularly in 

 our summer and fall months, haul more and more toward the south 

 as they approach the equator. The tracks of vessels bound to 

 India from Europe show this in a very striking manner. They 

 cross the equator generally about the meridian of 20° west ; there 

 they find the wind from southeast, frequently from south-south- 

 east, which forces the vessel offupon a course west of south. As 

 the vessel gets south, the winds haul more and more to the east, 

 so that, before clearing the belt of the southeast trades, the India- 

 bound trader is steering to the east of south. 



768. That the land of the northern hemisphere does assist to 

 turn these winds is rendered still more probable from this circum- 

 stance : All the great deserts are in the northern hemisphere, and 

 the land-surface is also much greater on our side of the equator. 

 The action of the sun upon these unequally absorbing and radiat- 

 ing surfaces in and behind, or to the northward, of the northeast 



