The rivers which reach the ocean do not ac count for the whole drainage of Africa. There are two great and numerous smaller tracts from which no large river reaches the sea. The two great areas of internal drainage correspond with the two, great deserts. That of the north desert is estimated at 4,000,000 square miles. As already indicated, it is furrowed with water courses in every direction, which lose them selves in the sand. The Bahr-el-Ghazal, which is usually dry, but intermittently flows out of Lake Tchad, terminates in a salt lagoon on the border of the desert to the north of the lake. In the south the Zuga or Botletle, which forms the outlet of -Lake Ngami, in the Kalahari desert, loses itself in salt lagoons at greater or less distance, according to the supply of water. A region of inland drainage, with salt lagoons, also exists between the Victoria Nyanza and the coast range of mountains. In the low coast land east of Abyssinia the Hawash River loses itself in the sands before reaching the sea; and the Webi, as already stated, which flows south from the Somali Peninsula to near the equator, likewise terminates in a salt lagoon on the border of the ocean. The Omo flows into the north end of Lake Rudolf.
The only lake of considerable ex tent north of lat. N. is Lake Tchad, an enormous flooded swamp subject to great varia tions of level and area (10,000-20,000 square miles), which until 1911-12 seemed to be drying up but since then has slowly increased in size. Lake Tsana in Central Abyssinia, the salt Lake Asal in the east and Lakes Dembel and Abayo in Gallaland, are comparatively small. Between 5° N. and 15° S. is a series of lakes forming one of the most striking features of the continent. Almost in a line, beginning in the south, are Lakes Nyassa, Tanganyika, Lifu, Albert Edward, Albert, all lying in more or less elongated rifts or gorges. The series is continued by Lakes Rudolf (salt) and Stefanie in the northeast, and, according to some authori ties, by the ancient lake now the Red Sea and by the Dead Sea in Palestine. The great Vic toria Nyanza, c. 32,167 square miles, the largest fresh water lake in the world after Lake Superior, which touches the equator on the north, is of a different type, as are Lake Bang weolo (another flooded swamp) on the south of Tanganyika and Lake Mweru in the north of Bangweolo. Lake Rikwa or Leopold, be tween Nyassa and Tanganyike, is partly of the rift type, while Lake Ngami in the Kalahari region is a swamp which sometimes dries up. Lake Leopold II and Lake Malumba are at tached to the lower Kongo. Lake Dilolo is in the swampy region forming part of the water shed between the Kongo and the Zambezi. There are numerous salt lagoons in the north ern portion of the Sahara.
Climate.— The climate of Africa is mainly influenced by the fact that, except the countries on the north and south coasts, it lies almost entirely within the tropics. The equator, as al ready observed, cuts it nearly through the mid dle, so that it belongs in latitudinal, though un equally in longitudinal extension, to the north and south tropics. It is the only continent which extends unbroken from the north to the south tropics and is consequently the hottest of all. The two sections north and south of the equator have, as has already been observed, in some respects a very considerable resemblance in their general features, the chief modifying circumstances being the greater elevation and the smaller longitudinal extension of the southern division, which, by bringing it more within the influences of the ocean, tends to modify its climate.
In the belt immediately under the equator, both north and south, vegetation is intense and rain abundant. For about 10 degrees north and south we find true tropical forests, mainly to the west of the great lakes, on the middle and upper Kongo and its affluents and along a belt of the west coast in the Niger region. To the east of the great lakes, where the rainfall is not so abundant, are considerable areas of poor steppe and scrub country, and generally over the tropical region the trees are scattered and the country more park-like than forestal. Ani
mal life, from herds of elephants to innumer able swarms of insects, abounds in these luxuri ant regions. To the north and south of the equatorial belt, as the rainfall diminishes, the forest region is succeeded by open pastoral and agricultural country. This pastoral belt ex tends, in the north, across the Sudan, from Senegambia to Abyssinia; on the south from Angola and Benguela to the Zambezi. This is followed by the rainless regions of the Sahara on the north and the Kalahari desert on the south, extending beyond the tropics and border ing on the agricultural and pastoral countries of the north and south coasts, which lie entirely in the temperate zone.
The winds and rains in Africa are chiefly produced by the successive exposure of the various intertropical belts to the vertical rays of the sun. The south winds on the west coast and the monsoons of the Indian Ocean exercise the principal modifying influence. From March to September the southwest monsoon blows from Africa to Asia, and during the remaining months the northeast monsoon blows toward the African coast. The indraught of air charged with moisture, at the seasons when the sun is overhead, produces the rainy seasons within the tropics, and as the incessant rarefaction of the air by heat continually draws in fresh supplies, the rainfall is on the whole abundant, varying from 50 to 100 inches in the region between 10° N. and the Tropic of Capricorn. In a patch on the Gulf of Guinea the rainfall exceeds 350 inches, though in Somaliland there are almost rainless patches. Near the tropics, to which the sun comes only once a year, there is only a sin gle rainy season, while in the central part of the zone, which the sun traverses twice in his pas sage between the tropics, there are two distinct rainy seasons, a greater and a less, according as the wind is in a direction which brings more or less moisture, except in some places in the in terior, where the two rainy seasons are so pro tracted as to blend into one, lasting, as in the Manyuema country, from September to July, or in some other parts even longer. The rainy season usually begins soon after the sun has reached his zenith, but on the east coast the monsoon charged with the moisture of the Indian Ocean brings it earlier. In the deserts, as already observed, there is hardly any rain; and this applies also to Egypt, which but for the Nile would be no better than the Sahara. The chief cause of the rainlessness of the des erts is the direction of the winds, which causes the chief moisture-bearing currents to pass, be fore reaching them, over hot and thirsty re gions which deprive them of their moisture; and especially the mountain screens which in tercept the moisture of the winds both from northeast and southwest. Another cause is the want of elevated regions to attract the moisture actually contained in the atmosphere, as in the higher regions of the desert periodical rains do occur. The high mountains of the east plateau and the intervening tropical regions deprive the northeast monsoon of all its moisture be fore it reaches the Kalahari desert. Hence the apparently anomalous circumstance that the greatest heat is found after the equatorial re gion is passed. The rapid radiation of heat in the desert causes a very great fall of tempera ture after the sun is down, so that sometimes frosts are generated, and this in some measure supplies the want of rain by condensing the moisture in dew. In the desert, too, scorching winds are generated full of fine particles of sand, those of the north afflicting Egypt and the countries on the Mediterranean coast and those on the west coast known as the harmat tan. The average summer temperature in the Sahara is 97 degrees or more; the hottest part is in Nubia, where the Arabs say the soil is like a fire and the wind like a flame. The coasts of tropical Africa, especially the west coast, where colonial settlements have been formed, have been found to have a deadly climate for foreigners.