Though far inferior to these streams of the western world in point of length and volume, the Nile of the ancient continent may be placed at the head of remarkable rivers. One of its chief peculiarities is the solitary grandeur of its flow; for not a single affluent enters it from the junction of the Tacazze to the sea, a distance of 1500 miles--a circumstance without a parallel in the physical condition of rivers. Another of its striking features is its long course through a desert, dry, barren, and hideous, depositing by its annual inundation the richest soil on those portions of it which lie contiguous to its banks; and hence has originated the apt comparison of its career to the path of a good man amidst an evil generation. Egypt would be completely sterile were it not for the periodical overflow of its only stream, which both covers a large part of its surface with a layer of alluvion, and imparts to it the requisite moisture.
“Rich king of floods! o’erflows the swelling Nile-- ----glad to quit The joyless desert, down the Nubian rocks From thund’ring steep to steep he pours his urn, And Egypt joys beneath the spreading wave.”
It requires the river to attain a medium rise in order to benefit the country: too little, involving scarcity and famine; too much, compromising the safety of the people and their dwellings. Wilkinson calls a rise of 19 cubits, tolerable; 20, good; 21, sufficient; while a rise of 22 cubits is abundant enough to fill every canal, and a rise of 24 cubits would overwhelm and ruin the villages. A cubit is rather more than 21 inches; so that, in order fully to meet the wants of the country, a perpendicular rise of 38 feet is necessary. The Nile is also distinguished among rivers for the pleasant taste and salubrity of its waters when not in flood; properties highly extolled by the ancients, and acknowledged to belong to it by modern travelers. It is a common saying with the Egyptians, that if Mahomet had tasted of its stream, he would have sought a terrestrial immortality in order to enjoy it forever. The physical circumstances of the river easily account for the possession of this attribute. The air above is pure and serene. But little rain falls upon the country through which the greater part of its course is prosecuted, and no snow or hail. Hence there is little drainage into it from the surrounding land, and its waters are kept free from any noxious taint derived from earths and minerals, except from those in its immediate channel. The same property of being remarkably pure and salutary is ascribed by Herodotus to one of the Susianic rivers, of which alone, according to tradition, none but the kings of Persia drank.