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.