530 SOURCE OF MOISTURE. Chap. XXV. 



the observations made for a number of years at Loanda, 

 by the late Edmund Gabriel, that the same rule as to rain- 

 fall, which we have noticed from 12° to 20° south, applies 

 in the eighth degree from the Equator. 



The great source of the supply of moisture for South 

 Africa is undoubtedly the Indian Ocean. The prevailing winds 

 are from the east or south-east. Laden with moisture from 

 this great reservoir, the air sweeps up the coast-ranges, and 

 cooling in its passage over, deposits the chief portion of its 

 aqueous vapour on the heights. Passing westwards, it is now 

 the dry air that floats, during most of the year, as an east, or 

 east-south-east wind, over the Kalahari Desert, and other arid 

 plains. That this view is correct appears evident from the 

 facts, that where no coast-range, or only a low one, exists the 

 central region is not so devoid of moisture, as it is where, as 

 in the case of the Drakensberg, the air must rise upwards of a 

 mile in perpendicular height, before it can reach the plains 

 beyond ; and that wherever hills in the interior rise higher 

 than those near the coast, their tops are covered with vegeta- 

 tion different from that on the plains below them, and 

 requiring a more abundant supply of moisture. This is seen 

 even on the hills close to the Kalahari Desert ; and on other 

 mountain-tops many species of ferns and some peppers 

 flourish, which are never met with at lower altitudes. 



As we approach nearer the Equator, the south-west winds 

 from the Atlantic, robbed of their moisture by the western 

 slopes, prevail for a certain distance into the continent, 

 and probably meet the south-easterly breezes from the Indian 

 Ocean. Whether this meeting produces a greater amount 

 of rainfall on the Line than elsewhere, as has been 

 asserted, appears to require confirmation. Theoretically, the 

 confluence of dry winds under the Equator, would be followed 

 by an upward and overlapping motion of the currents to the 



