The Nile is one of the world's _great_ rivers, and is about 3,400 miles long. As you will see, it has its source in the overflow from Lake Victoria Nyanza, when it flows in a generally northern direction for many hundreds of miles, receiving several tributaries, such as the River Sobat and the Bahr-el-Ghazal, whose waters, combining with the Bahr-el-Abiad, or White Nile, as it is called, maintain the steady constant flow of the river. Eventually it is joined by the Bahr-el-Azrak, or Blue Nile, which rises among the mountains of Abyssinia and enters the White Nile at Khartūm. During a great part of the year this branch is dry, but filled by the melting snow and torrential rains of early spring, the Blue Nile becomes a surging torrent, and pours its muddy water, laden with alluvial soil and forest débris, into the main river, causing it to rise far above its ordinary level, and so bringing about that annual overflow which in Egypt takes the place of rain. It is certain that the ancient Egyptians knew nothing as to the source of their great water-supply,[4] their knowledge being limited to the combined river which begins at Khartūm, and for 1,750 miles flows uninterruptedly, and, with the exception of the River Atbara, without further tributaries until it reaches the sea; and it is curious to think that for every one of these 1,750 miles the Nile is a _slowly diminishing_ stream, water-wheels, steam-pumps, and huge arterial canals distributing its water in all directions over the land. The large number of dams and regulators constructed within recent years still further aid this distribution of the Nile water, and it is a remarkable and almost incredible fact that with the closing of the latest barrage at Damietta, the Nile will be so completely controlled that of all the flow of water which pours so magnificently through the cataracts not a drop will reach the sea! [Footnote 4: Many of the ancients believed the First Cataract to be its source.] One can easily understand the reverence with which the ancients regarded their mysterious river, which, rising no one knew where, year by year continued its majestic flow, and by its regular inundations brought wealth to the country, and it is no wonder that the rising of its waters should have been the signal for a series of religious and festal ceremonies, and led the earlier inhabitants of Egypt to worship the river as a god. Some of these festivals still continue, and it is only a very few years since the annual sacrifice of a young girl to the Nile in flood was prohibited by the Khedive.