Nile, the longest river of Africa, of the greatest interest historically and geographically, and to the ancient Egyptians pre-eminently the sacred river, draws its largest supplies of water from the Victoria and Albert Nyanzas. Its furthest head-streams (Shimiyu, Isanga, etc.) flow into the Victoria Nyanza from the south. The Nile leaves Victoria Nyanza at its northern end, pouring over the Ripon Falls, 150 to 170 yards wide but only 12 feet high, and then for 300 miles races between high rocky walls, over rapids and cataracts, at first north-west, then west, until it joins the Albert Nyanza (q.v.) near its north-east corner. About 20 miles from this lake the river leaps down 120 feet into a wild gorge, with high rocky walls. The section between the two Nyanzas is called the Victoria Nile or Somerset River. At its south-western extremity the Albert Nyanza is joined by the river Semliki, which drains the Albert Edward Nyanza. The combined river leaves the northern extremity of the Albert Nyanza as the Bahr-el-Jebel, and from that point flows in a general northerly direction to the Mediterranean. At Lado (5° N. lat.) it enters the plains, and moves thence slowly and sluggishly down to Khartoum, 900 miles to the north. The whole of this stretch is navigable for fairly large river-steamers. In 7 1/2° N. lat., however, the main channel divides into two arms, which flow, at no great distance apart, through a low swampy region. In 9 1/2° N. lat. the Bahr-el-Jebel is met by the Bahr-al-Ghazal from the west, which gathers the waters of many rivers. Sixty miles east of the confluence the river, now called White Nile, receives the Bahr-el-Zeraf, and 30 miles farther east still the Sobat, from the Galla country. Hence the White Nile flows almost due N. to Khartoum without receiving a single tributary. At Khartoum (in 15° 37' N. lat.) the White Nile, or Bahr-al-Abiad, is joined from the south-east by the Blue Nile, the Bahr-al-Azrak, 950 miles long, from Lake Tana (5658 feet above sea-level) on the Abyssinian plateau. From Khartoum the Nile flows north-north-east, and 200 miles below that city is joined from the right by the Atbara or Black Nile. In its course through the Nubian Desert the great river makes two deep bends, first round by the north, then round by the south, and subsequently resumes its northerly flow. Below Khartoum navigation is rendered extremely dangerous by the cataracts which obstruct the bed of the river, the sixth occurring not far north of Khartoum, the first near Assouan, in Egypt, just above 24° N. lat. The course of the river from Assouan to the sea, its inundations, etc, are described under Egypt (q.v.). The total length of the river cannot be stated precisely; from Victoria Nyanza it is estimated to measure 3400 miles. Irrigation is largely regulated by the great Nile Barrages at Rosetta and Damietta, constructed by French engineers in 1843-61, and practically reconstructed by British engineers in 1886-90 at a cost of £405,000; and by the immense dams at Assouan (completed 1902) and Assiout, at a total cost of nearly £5,000,000.
The ancients had little authentic knowledge of the Nile above Meroe, half-way between Berber and Khartoum. The Emperor Nero began the work of searching for the sources of the Nile by sending two expeditions into Nubia. Ptolemy speaks of two streams issuing from two lakes 6 and 7 degrees south of the equator and uniting in 2° N. lat., and being joined in 12° N. lat. by the Astapus, which likewise flowed from a lake (Coloe). The two lakes in the far south were fed by the melting snows of a great range of mountains, the Mountains of the Moon. This remained the sum total of information about the river down to the 19th century, except that in 1770 Bruce discovered that the Blue Nile issued from Lake Tana. The Egyptian government in 1839-42 sent three expeditions as far as Gondo-koro. In 1858 Speke reached the Victoria Nyanza, in 1860 Sir Samuel Baker discovered Albert Nyanza, and in 1868-71 Schweinfurth explored the western feeders of the White Nile. Stanley, in 1875, sailed all round Victoria Nyanza, and in 1889 traced the course of the Semliki, and discovered Albert Edward Nyanza and Mount Ruwenzori. The British occupation of Uganda, between the Victoria and Albert Nyanzas, and the arrangement made with the Congo State in 1894, tended to retain the whole valley of the Nile, from the Nyanzas to the Mediterranean, under British influence.