THE CLIMATE OF AFRICA.
We have considered the climate of Africa but incidentally in connection
with the sections which we have viewed. It will be of interest to note
the changes in its character in connection with the form of the
continent.
While Africa lies almost entirely within the torrid zone, and is
therefore the hottest country known to us, yet it presents three great
varieties of climate. These correspond with its physical structure.
Hence, we find the plateaus, the terraces which lead to them, and the
coasts, showing great varieties of climate, though lying very nearly in
the same latitude.
The highest temperature is to the north of the equator. In Nubia and in
Upper Egypt the intense heat of the sun, acting upon the sands, renders
it possible to roast eggs in them; while, along the shores of the
Mediterranean the influence of the sea makes the climate much more
temperate.
In the vast desert of Sahara, which has an area equal in extent to that
of the Mediterranean Sea, and yet is almost destitute of water and
well-nigh barren of vegetation, we find the climate showing a uniform
yet striking contrast between the heat of the day and the coldness of
the night. Towards the south of the Sahara the country is more elevated
and consequently somewhat cooler. Some of the more elevated portions
near the equator reach the altitude of perpetual snow.
There is no regular fall of snow even in the northern or southern
portions of the continent. Radiation of the heat is very great in some
parts of Africa, as in the northern sections. The soil of the Sahara,
for instance, absorbs heat very rapidly during the day, but during the
night it radiates the heat still more rapidly, thus making a great fall
in temperature. So rapid is this radiation of heat that ice is said to
be formed sometimes during the night when water is left exposed to the
atmosphere.
In strong contrast to the hot days and cool nights of the Sahara is the
climate of the terraces of Limbu, situated behind the region of the
Sierra Leone. Here we find the climate not only temperate but wholesome;
while in the region behind the Slave Coast there are beautiful
landscapes, abundant springs, new forms of vegetation to delight eye or
palate, and an atmosphere as mild and balmy as that of sunny Italy.
In the regions of the Congo the natives call their terrace lands, which
are under cultivation and thickly populated, "The Paradise of the
World," suggestive of every detail of the beauty of the Garden of Eden,
when Adam and Eve were permitted to dwell in it.
The flat coasts of Africa are often flooded over in the rainy season.
This renders the climate very oppressive, owing to the humidity of the
atmosphere. From the morasses found around the mouths of the rivers a
malarious vapor arises, which is most destructive to health. Malarial
fever, when it attacks Europeans, is much of the nature of a pestilence
in its destruction of life.
This pestilential air along the coast region is supposed to be caused by
the decaying vegetable matter brought down from the dense mangrove woods
through which the rivers take their course in their journey to the sea.
As this decaying vegetable matter mingles with the salt water of the
sea, it forms a poisonous gas, sulphureted hydrogen, most fatal to
health. The air of these regions, freighted with this pestilential gas,
often extends for one hundred miles inland.
Out at sea we find this gas poisoning the air for about forty miles from
the coast, while it affects the atmosphere for about four hundred feet
above sea level. Hence, it would seem desirable to take up one's abode
either in the interior of such regions, far out at sea, or even in a
balloon, were it possible, rather than to breathe the pestilential
atmosphere of these coast terraces.
The influence of the regular winds is felt very little in Africa, with
the exception of what comes from the monsoons of the Indian Ocean. These
extend over possibly a third of the eastern shores, but they affect to a
considerable extent the whole of Africa. Hurricanes are sometimes felt
in the southeastern extremity, but rarely in any other portion.
The northern part of Africa is exposed to the hot winds and the storms
which sweep from the Sahara. These winds have a distinctive character
and are noted for their extreme dryness and heat. They often prove to be
most disagreeable and disastrous; for they not only lift the sand in
great volumes and fill the air with dust, but they prove fatal to animal
life and vegetation in any region over which they sweep.
The supply of rain in Africa is very scanty. As we have seen, the Sahara
is almost rainless, as is also the Kalahari Desert.
The clearness of the atmosphere of Africa exceeds that of any other
known parts of the globe. It has been a constant surprise and delight to
European astronomers, when making their explorations. With wonder and
amazement they have beheld the glory and the splendor of the African
heavens. With awe and admiration they have gazed at the planets shining
with great brilliancy and often making well-defined shadows, such as we
are accustomed to look for from our nearest neighbor, the moon, when it
is most brilliant during the harvest months.
The amount of rain which falls in Africa varies not only in the
different sections of the continent, as we have seen, but with the
season of the year.
To the regions between the Kawara and the Senegal the southeast trade
winds bring copious rains. It has been stated that at Sierra Leone as
much as one hundred and thirteen inches of rain have been known to fall
during the year. These summer monsoons, however, bring the largest
supply of rain to Africa upon its eastern coast. They last from April
till October, and bring rain to drench the extensive plains and elevated
grounds of the great eastern extremity of Africa.
The force of these winds becomes somewhat broken, and their influence
diminished, by the vast table-lands of Abyssinia. When the monsoon comes
from the Asiatic continent no rain falls in these regions.
The southeast monsoon extends north as far as Lake Tchad and Kordofan,
and even farther north. The influence of this monsoon is felt in May,
though along the coast it is usually felt a month later in the season.
This fact, it is believed, disproves the old theory that Central Africa
has a connected chain of high mountains. For, at the east, where lofty
mountains do exist, these same rain-bearing winds become seriously
interrupted and retarded. Hence, they do not reach the most northern
portions of Abyssinia until fully a month later than they reach Lake
Tchad.
The upper basin of the Nile, not far from the coast, no doubt receives
its supply of water with the beginning of the monsoon, and continues to
rise till September.
The many extremes of climate necessarily affect the vegetation of
Africa. In connection with such views of Africa as we have had, we have
gained some little knowledge of the vegetation, but it will be
interesting to gain a broader and more comprehensive knowledge in order
to understand the great diversity of animal life to be found in Africa.