Chap. XXIV. -CAUSES OF ARIDITY AND MOISTURE. 
477 
tliis 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 rehable information. This, it is to be hoped, will be 
one of the results of the researches of Captain Burton in liis 
present journey. 
The original valley formation of tlie 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 And 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 tlie 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- 
