Page:Africa by Élisée Reclus, Volume 4.djvu/386

 308 SOUTH AND EAST AFBICA. basin, cannot prevent the formation of a residuum of saline substances in this lacustrine reservoir, whose waters, according to native report, have a flavour of sulphur. Climate. To the Usagara ^fountains, rising between the plateau and the seaboard, are mainly due the contraste of climate, and consequently of all the phenomena depending on it, including those of the running or stagnant waters. In this region of East Africa the mean direction of the winds is normal with the coast. Whether the south-east trades are in the ascendant, as is the case during the greater part of the year, or whether they are succeeded by those of the north-east, as in the month of January, when the whole atmospheric system is shifted south- wards with the course of the sun, or whether the aerial currents are attracted to the interior of the continent, these currents always set in the direction of the coast. The rain-bearing clouds are thus arrested by the mountain ranges of the interior. For the same reason the alternating daily breezes are felt only on the maritime slope. Hence the opposite side facing landwards, as well as the inland plateaux sheltered from the prevailing easterly winds, are much farther removed from marine influences than might be supposed from their proximity to the Indian Ocean. The mnssi/cn, that is to say, the rainy season, during which the people remain " confined to their houses," generally begins on the coastlands in January, when the east winds are displaced by the north-east monsoon. But the heavy down- pours scarcely set in before March or April. After the month of May they fall off, returning again in the ru/i season, which lasts from the middle of October to the end of the year. September is the driest month, although even then occasional showers occur. In certain inland valleys opening in the direction of the moisture- charged winds, it rains throughout the whole year, except perhaps for a fortnight or so in September. Here the massika makes its appearance much sooner than on the coast, and the mountains are frequently wrapped in dense fog. The total rainfall certainly exceeds 120 inches on the seaward slope of the Usagara uplands. The same contrast that is observed towards the southern extremity of the con- tinent between the Atlantic and Indian Ocean seaboards, is also maintained in these tropical regions lying between the tenth and sixth degrees of south latitude. At equal distances from the equator both the rainfall and the temperature are higher on the east than on the west coast. According to Hann, the difference of temperature under the tenth degree of south latitude, that is about the Rovuma and Cuanza estuaries respectively, is as much as eight degrees Fahrenheit, a contrast which must be attributed to the direction of the marine and aerial currents on the two coasts. The monsoons on the Atlantic side blow almost constantly from the south, and are consequently tempered by the cold Antarctic waters. But on the opposite side of the continent the prevailing winds come from the east, that is by an oceanic basin heated by the vertical solar rays.*. The contrast is even greater • Temperature of the west coast of Africa, 72° F. ; temperature of the east coast of Africa, 80° F.