Chap. XXI?. CAUSES OF ARIDITY AND MOISTURE. 477 



this may be, the phenomena of the rainy season show that it is 

 not necessary to assume the existence of high snowy mountains, 

 until we get reliable information. This, it is to be hoped, will be 

 one of the results of the researches of Captain Burton in his 

 present journey. 



The original valley formation of the continent, determined the 

 northern and southern course of the Zambesi in the centre, and 

 also of that ancient river which once flowed from the Linyanti 

 basin to the Orange river. It also gave direction to the southern 

 and northern flow of the Kasai and the Nile. We find that be- 

 tween the latitudes, say 6° and 12° S., from which, in all proba- 

 bility, the head waters of these rivers diverge, there is a sort of 

 elevated partition in the great longitudinal valley. Presuming 

 on the correctness of the native information, which places the 

 humid region to which the Nile and Zambesi probably owe their 

 origin, within the latitudes indicated, why does so much more 

 rain fall there than in the same latitudes north of the equator ? 

 Why does Darfur not give rise to great rivers, like Londa and 

 the country east of it? The prevailing winds in the ocean 

 opposite the territory pointed out are said to be from the N.-E. 

 and S.-E. during a great part of the year ; they extend their 

 currents on one side at least of the equator, quite beyond the 

 middle of the continent, and even until in Angola they meet the 

 sea-breeze from the Atlantic. If the reader remembers the 

 explanation, given at page 95,* that the comparative want of 



* Since the explanation in page 95 was printed I have been pleased to 

 see the same explanation given by the popular astronomer and natural 

 philosopher M. Babinet, in reference to the climate of France. It is quoted 

 from a letter of a correspondent of the Times in Paris : — 



" In the normal meteorological state of France and Europe, the west 

 wind, which is the counter-current of the trade-winds that constantly 

 blow from the east under the tropics — the west wind, I say, after having 

 touched France and Europe by the western shores, re-descends by Mar- 

 seilles and the Mediterranean, Constantinople and the Archipelago, 

 Astrakan and the Caspian Sea, in order to merge again into the great 

 circuit of the general winds, and be thus carried again into the equatorial 

 current. Whenever these masses of air, impregnated with humidity 

 during their passage over the ocean, meet with an obstacle, such as a 

 chain of mountains, for example, they slide up the acclivity, and, when 

 they reach the crest, find themselves relieved from a portion of the column 

 of air which pressed upon them. Thus, dilating by reason of their elas- 



