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- 
Avard 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 southwest 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 wind 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 
