Egypt, Arabia, etc., or subject to a
dry season by the northern ascent of the southern line of the
extra-tropical belt, as the Barbary States, Syria, Persia, etc., and their
supply of moisture is necessarily scanty. On the south, the S. E. trades
originate, in part, upon the eastern portion of southern Africa, and, in
part, upon the Indian Ocean, and from the latter source, and a portion of
the Mediterranean, doubtless most of the water which falls upon Central
Africa, is derived.

The N. E. and S. E. trades which blow into the inter-tropical belt upon
the eastern portion of the Atlantic, originate upon similar surfaces, and
with like effect. Thus, the S. E. trades, in summer, are from the Southern
portion of Africa, and the N. E., in part, from the Mediterranean; and, in
winter, the N. E. from the deserts, Senegambia, Nigritia, etc., and the S.
E., owing to the narrowing of the African continent, mainly from the South
Atlantic and Indian Oceans. Going west, the belt widens, and its range
increases until the Andes are reached; but under their lee, on the western
side, a totally different state of things is found, and the belt of the
coast becomes broken and irregular, as we have seen in the citation from
Maury.

The width, extension, and excessive precipitation of the belt, over South
America, follow the same law. The South Atlantic widens out by the
trending of the coast to the S. W., and furnishes a large area for the
unobstructed formation and evaporative action of the S. E. trades. So the
trending of the coast to the N. W., from 5 deg. south to the northward, opens
a large area for a like formation and action of the N. E. trades. No
correspondingly favorable circumstances exist any where, except, perhaps,
around Hindoostan, and there the fall of rain is very excessive in some
places, as on the Kassaya hills, to the extent of 400 inches per annum. In
addition to this, the magnetic line of no variation, and of greater
intensity, which runs from our magnetic pole, obliquely, S. S. E., to its
opposite and corresponding pole in the southern hemisphere, enters the
Atlantic on the coast of North Carolina, and traverses it, and the eastern
portion of South America, through the whole trade-wind region. The
table-lands, and slopes, and high mountain peaks, meet the trades
successively, as they go west, and the latter wrench from them, to an
unusual extent, their moisture; depressing the line of perpetual snow, by
an increas