The Atbara, also called Bahr-el-Aswad, or Black river, because it carries down with it the greatest amount of the black mud and slime that manures and fertilizes Egypt, is the last tributary received by the Nile. seems to be the direct source of the Atbara. It rises in the heights to the n. of lake Dembea. About 150 in. from its .source it receives the Basalam river, and about 30 m. further on, the Takazze or Setit river, both from the east. The Takazze has a far greater volume of water than either of the preceding rivers. It rises in the Sameu mountains, round which it flows first east erly, then n., till in about lat. 13° 30' n., long. 38° 50' e. it -turns n.w., and then almost -due w., joining the Atbara at right angles. It has many tributaries.
From its junction with the Atbara the Nile continues to flow northerly through the populous and fertile district of Berber, full of villages, and then enters the desert. Turn ing westwards in lat. 19° n., it forms the large island of Mograt, and makes a curve to the south-westward, known as the "great bend." in which there are two cataracts. _Entering Nubia, the Nile resumes its northwesterly course, with narrow strips of culti vated land on each bank. Here it forms another cataract, and bends round to the n.e. with a fifth cataract, in lat. 21° 40' north. After this the valley of the Nile narrows, and at Assouan, in lat. 24° 10' n., it forms the last cataract in descending.
From Assouan to the sea the average fall of the Nile is two inches to a in., and its mean velocity about three m. an hour. It waters and fertilizes the whole length of the land of Egypt. The delta of the Nile extends from lat. 30° 10' n. to 31° 30' n., and has a base on the Mediterranean of about 150 miles. In it the Nile spreads out into numerous streams, the two principal being those of Rosetta and Damietta. The total length of the :Cite, from its exit from the lake to the sea, is about 3,300 m., measured along its course, -or about 2,200 m. direct distance.
A feature peculiar to the river of Egypt is that from its junction with the Atbara, to its mouth, a distance of upwardg of 1500 m., it receives no affluent whatever, and yet it is .able to contend with the burning sun, and scarcely less burning sands of Nubia. With the ancient Egyptians the river was held sacred: the god Nilus was one of the lesser divinities. Its annual overflow is one of the greatest marvels in the physical geography -of the globe for it has risen to within a few hours of the same time, and to within a few inches of the same height, year after year for unknown ages. At Khartoum it begins to increase early in April, but in lower Egypt the inundation usually begins about the 25th 'of June, and attains its height in about three months. It remains stationary about twelve
-days, and then subsides. The cultivable soil of Egypt is wholly dependent on the rise -of the Nile, and its failure causes a dearth; for, virtually, the country has no rain. Con tinuous south wind brings a good, and north wind a had year. During a good inunda tion the rise is about 40 ft. on the tropic of Capricorn, 36 ft. at Thebes, and 4 ft. at the Damietta and Rosetta mouths in the Delta. If at Cairo the rise is only 18 or 20 ft. there is a scarcity; up to 24 ft., a deficiency; 25 to 27 ft. is good: more than that causes a flood, and fosters plague and murrain. During the inundation the whole valley is cov ered with water, from which the villages rise like protected by dikes. Of late years the overflow has been greater than the average of many centuries. The rise and fall of the trunk stream of the lower Nile is owing to the periodicity of the rains on the mountains of Abyssinia and in the basin of lake Nyanza, where, on the equator, it rains, more or less, all the year round, most copiously during the equinoxes. The banks of the Nile swarm with birds, among which are vultures, cormorants, geese, pelicans, quails, and the white ibis; and its sweet, soft waters teem with fish. The average amount of alluvium brought down by the river is estimated at a deposit of 44- inches in a century— by some it is made as high as 6 inches; the greater part of it is brought down by the Atbara The question of the source of the Nile is at once the oldest and the most recent of geography. That the sources of a river, at whose mouth one of the earliest and most civilized peoples was established, should have been so long veiled in obscurity is unpar alleled in geographical research. The want of success in exploring the upper basin of the Nile may be attributed to the great length of the to the difficulties which beset the in the physical nature of the countries he must pass through, the climate, and the jealousy, ignorance, and barbarism of the native tribes. This problem of centuries may now be regarded as satisfactorily solved; for the question whether there may not yet be found important feeders of the White Nile carrying back its source to a still greater distance in the interior is practically excluded by Stanley's exploration of the Lualaba or•Congo basin. The journeys of Krapf and Rebmann to the foot of Kilimand jaro and the other snowy mountains in the e. of Africa, believed by them to be the ancient "mountains of the moon," and the explorations of the White Nile, pointed to the conclusion that it was among these mountains that the sources of the great river would ultimately be discovered.