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 109,* that the comparative want
of rain on the Kalahari Desert is caused by the mass of air losing its
humidity as it passes up and glides over the subtending ridge, and will
turn to the map, he may perceive that the same cause is in operation
in an intense degree by the mountains of Abyssinia to render the region
about Darfur still more arid, and that the flanking ranges mentioned lie
much nearer the equator than those which rob the Kalahari of humidity.
The Nile, even while running through a part of that region, receives
remarkably few branches. Observing also that there is no known abrupt
lateral mountain-range between 6 Deg. and 12 Deg. S., but that there is
an elevated partition there, and that the southing and northing of the
southeasters and northeasters probably cause a confluence of the two
great atmospheric currents, he will perceive an accumulation of humidity
on the flanks and crown of the partition, instead of, as elsewhere,
opposite the Kalahari and Darfur, a deposition of the atmospheric
moisture on the eastern slopes of the subtending ridges. This
explanation is offered with all deference to those who have made
meteorology their special study, and as a hint to travelers who may have
opportunity to examine the subject more fully. I often observed, while
on a portion of the partition, that the air by night was generally quite
still, but as soon as the sun's rays began to shoot across the upper
strata of the atmosphere in the early morning, a copious discharge came
suddenly down from the accumulated clouds. It always reminded me of the
experiment of putting a rod into a saturated solution of a certain salt,
causing instant crystallization. This, too, was the period when I often
observed the greatest