Nile

On the island of Elephantine at Assuan is the famous Nilometer, dating from ancient Egyptian times, altered and extended in Roman times and repaired in 187o by the Khedive Ismail. It is a stairway in the river quay wall built of hewn stones, marked with scales to record the level of the water of the river. The 'By Sir Hanbury Brown, inspector-general of irrigation, Lower Egypt, 1892-1903.

remains of other ancient Nilometers exist at Philae, Edfu and Esna, together with inscriptions recording about forty high Niles in the XXVth Dynasty, discovered on a quay wall of the temple of Karnak. The data furnished by these give about 44 in. per century as the average rate at which the Nile is silting up its bed north of the 1st cataract. The present level of high Nile at the Semna rapids, between the 2nd and 3rd cataracts is 24 ft. lower than that indicated by the marks sculptured c. 2500 B.C. This fall is attributed to the erosive action of the water as it passes over the hard gneiss which at Semna forms a barrier across the stream. The vertical extent of such erosion is equal to about two milli metres a year. There are now gauges for registering the rise of the water at Cairo, Assuan, Berber and Khartoum on the main river; at Wad Medani, Sennar and Roseires on the Blue Nile; El Duem and Malakal on the White Nile; Nasser on the Sobat; Mongalla on the Bahr-el-Jebel; and Ugowe, Jinja and Entebbe on Victoria Nyanza.

Navigation.

At high Nile there is uninterrupted water communication from the sea to Fort Berkeley in 4° 40' N.— a distance of 2,900 m. Owing to the cataracts, navigation between Assuan and Khartoum is impossible during low Nile, and from March 1st to Aug. 1st the upper courses of the Damietta and Rosetta branches are closed to navigation ; the water being utilized for summer irrigation in the delta. As far as Mansura (6o in.) on the Damietta branch and Kafr-el-Zayat (7o m.) on the Rosetta branch, and between Khartoum and Fort Berkeley (1,090 m.) the river is navigable all the year round, though between the Sobat confluence and Bor, navigation is dependent on the channel being kept clear of sudd. Above Fort Berkeley navigation is interrupted by the rapids and cataracts which extend to Dufile, but from the last-named town to Fajao at the foot of the Murchison Falls (a distance of 150 m.) the river is navigable throughout the year. There is a further navigable stretch between Foweira (just above the Karuma rapids) and the southern end of Lake Kioga. The Blue Nile is navigable for steamers during flood time from its confluence at Khartoum to Roseires at the foot of the Abyssinian hills, a distance of 426 m. At low water small boats only can go upstream. The Atbara is never navigable, the current during flood time being too swift for boats. Including the Sobat and the Bahr-el-Ghazal the navigable waters of the Nile and its affluents exceed 4,000 m. (W. E. G.; F. R. C.) Story of Discovery.—Few problems in geographical research exercised for so long a period so potent an influence over the imaginations of man as that of the origin of the Nile. The ancient Egyptians, as is apparent from the records on their monuments, were acquainted with the main stream as far south as the junction of the White and Blue Niles. They appear also to have known the Blue Nile up to its source and the White Nile as far south as the Bahr-el-Ghazal confluence. Beyond that point the sudd probably barred progress. The knowledge acquired by the Egyp tians passed to the Persians and Greeks. Herodotus (about 457 B.c.) ascended the Nile as far as the First Cataract. He was led to believe that the source of the river was far to the west—in the region of Lake Chad. Eratosthenes, superintendent of the Alexan drian library, in a map made about 25o B.c., showed, with fair accuracy, the course of the river as far as where Khartoum now stands. He showed also the Atbara and Blue Nile. Eratosthenes was the first writer to hint at equatorial lakes as the sources of the river. Juba II., king of Mauretania (who died about A.D. 20), in his Libyca, quoted by Pliny, makes the Nile rise in western Mauretania, not far from the ocean, in a lake presenting charac teristic Nile fauna, then pass underground for several days' journey to a similar lake in Mauretania Caesariensis, again con tinue underground for twenty days' journey to the source called Nigris on the borders of Africa and Ethiopia, and thence flow through Ethiopia as the Astapus. This remarkable story received considerable credence, and may be connected with the theory which made the Niger a branch of the Nile (see below). Strabo (a contemporary of Juba), who ascended the river as far as Syene, states that very early investigators had connected the inundation of the Lower Nile with summer rains on the far south ern mountains, and that their theory had been confirmed by the observations of travellers under the Ptolemies. About the same time Dalion, a Greek, is believed to have ascended the White Nile. Nero despatched two centurions on an expedition for the express purpose of exploring the Nile, and Seneca states that they reached a marshy impassable region, which may be easily identified with the country of the White Nile above the mouth of the Sobat.

To what they referred when they reported a great mass of water falling from between two rocks is not so readily determined. During this period more accurate knowledge concerning the Nile sources was obtained from the reports of Greek traders who visited the settlements on what is now called the Zanzibar coast. A merchant named Diogenes returning (about A.D. 5o) from the east coast of Africa told a Syrian geographer, Marinus of Tyre, that journeying inland for twenty-five days he reached the neigh bourhood of two great lakes and a range of snow mountains whence the Nile drew its sources. Marinus published this report in his geographical works. This book is lost, but the information is incorporated in the writings of Ptolemy, who in his book and map sums up all that was known or surmised of the Nile in the middle of the 2nd century of the Christian era. Ptolemy writes that two streams issuing from two lakes' (one in 6° and the other in 7° S.) unite in 2° N. to make the Nile, which, in 12° N., receives the Astapus, a river flowing from Lake Coloe (on the equator). His two southern lakes, he conceived, were fed by the melting of snows on a range of mountains running east and west for upwards of 50o m.—the Mountains of the Moon, TO rijs Opos, Lunae Montes. It will be seen that, save for placing the sources too far to the south, Ptolemy's statements were a near approximation to the facts. The two southern lakes may be identified with the Victoria and Albert Nyanzas, and Lake Coloe with Lake Tsana. The snow-capped range of Ruwenzori occupies—at least in part—the position assigned to the Mountains of the Moon, with which chain Kilimanjaro and Kenya may also be plausibly identified. On all the subsequent history of the geography of the Nile Ptolemy's theory had an enormous influence. Mediaeval maps and descriptions, both European and Arabian, reproduce the Mountains of the Moon and the equatorial lakes with a variety of probable or impossible modifications. Even Speke (see p. 456) congratulated himself on identifying the old Ptolemian range with the high lands to the north of Tanganyika, and connected the name with that of Unyamwezi, the "country of the moon." In the fourteen centuries after Ptolemy virtually nothing was added to the knowledge of the geography of the Upper Nile. Arab writers of the 12th and 13th centuries make mention of the great lakes, and their reports served to revive the interest of Europe in the problem of the Nile. Idrisi made both the Nile and the Niger issue from a great lake, the Niger flowing west, the Nile north. Hence arose much confusion, the Senegal estuary being regarded by its discoverers as the mouth of a western branch of the Nile. Even until the early years of the 19th century the belief persisted in a connection between the Nile and the Niger (see further NIGER). Portuguese explorers and missionaries, who in the 15th and 16th centuries visited the east coast of Africa and Abyssinia, gained some information about the equa torial lake region and the Nile, the extent of the knowledge thus acquired being shown in the map of Africa of Filippo Pigafetta, Italian traveller and historian (1533-1603) published in 1580. It was not, however, till the 57th century that the sources of the Blue Nile were visited by Europeans. In 1615 Pedro Paez, a Portuguese priest, was shown them by the Abyssinians. Ten years later another Portuguese priest, Jeronimo Lobo, also visited the sources and left a vivid description of the rise of the river and its passage through Lake Tsana. An English version of the accounts of Paez and Lobo—written by Sir Peter Wyche—was published in 1669 by order of the Royal Society, of which Sir Peter was an original Fellow. Between 1625 (the date of Lobo's visit) and 1770, some attempts were made by French and other 'The two lakes afterwards received the names Lake of Crocodiles and Lake of Cataracts_ travellers to explore the Blue Nile, but they ended in failure. In the last-named year James Bruce (q.v.) reached Abyssinia, and in Nov. 1772 he arrived in Egypt, having visited the source of the Blue Nile and followed it, in the main, to its confluence with the White Nile. On returning to Europe Bruce was mortified to find that whilst he was still in Egypt the French geographer D'Anville had (1772) issued a new edition of his map of Africa in which by a careful study of the writings of Paez and Lobo he had anticipated Bruce's discoveries, D'Anville's map is singularly accurate, if we remember the scanty information at his disposal. To Bruce, nevertheless, belongs the honour of being the first white man to trace the Blue Nile to its confluence with the White Nile. He himself, considering the Blue Nile as the main branch of the river, claimed to be the discoverer of the long-sought caput Nili.