The earth and its inhabitants .. earthitsinhabita0186recl Year: 1886 10 NOETH-EAST AFEICA. of the atmosphere, and enable the local vapours to condense and precipitate them- selves on the spot. In the northern hemisphere a zone of two wet seasons stretches from the equator to the fifteenth degree of latitude. In summer, copious rains are caused by the moisture-bearing south-west winds ; in winter, those blowing from the north-west become in their turn the bearers of heavy rain-charged clouds to the southern hemisphere. But on both sides of the torrid zone, which comprises about seven-tenths o
The earth and its inhabitants .. earthitsinhabita0186recl Year: 1886 10 NOETH-EAST AFEICA. of the atmosphere, and enable the local vapours to condense and precipitate them- selves on the spot. In the northern hemisphere a zone of two wet seasons stretches from the equator to the fifteenth degree of latitude. In summer, copious rains are caused by the moisture-bearing south-west winds ; in winter, those blowing from the north-west become in their turn the bearers of heavy rain-charged clouds to the southern hemisphere. But on both sides of the torrid zone, which comprises about seven-tenths of the whole continent, the difference in the disposition of the winds Fig. 4.—Isothermal Lines of Africa. Scale 1: 75,000,000. 1,200 Miles. causes a corresponding contrast in the rainfall. Here the trade winds maintain their normal direction constantly, or with but slight temporary deviations ; blowing from the north-east in the northern, from the south-east in the southern hemisphere, they divert to the equator most of the vapours crossing their path, leaving else- where clear skies and arid lands. Thus it happens that Africa has two almost com- pletely barren zones of rocks, gravels, marls, clay and sand—the Sahara and Libyan desert in the north, Kalahari and other wastes in the south. This
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