THE WINDS. 219 



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

 heated surfaces, and other such like inequalities. 



465. 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. 



466. That such is actually the case is rendered still more prob- 

 able from this consideration : All the great deserts are in the north- 

 ern 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 radiating surfaces in and behind, or to the north- 

 ward of the northeast trades, tends to retard these winds, and to 

 draw large volumes of the atmosphere, that otherwise would be 

 moved by them, back to supply the partial vacuum made by the 

 heat of the sun, as it pours down its rays upon the vast plains of 

 burning sands and unequally heated land surfaces in our over- 

 heated hemisphere. The northwest winds of the southern are also 

 and consequently stronger than the southAvest winds of the north- 

 ern hemisphere. 



467. The investigations that have taken place show that the in- 

 fluence of the land upon the normal directions of the Avind at sea 

 is an immense influence. It is frequently traced for a thousand 

 miles or more out upon the ocean. For instance, the action of 

 the sun's rays upon the great deserts and arid plains of Africa, in 

 the summer and autumnal months, is such as to be felt nearly 

 across the Atlantic Ocean between the equator and the parallel of 

 13° north. Between this parallel and the equator, the trade- winds 

 are turned back by the heated plains of Africa, and are caused to 



