35 EGYPT-THE COUNTRY.
and famine. During the reign of the Caliph Mustansir a period of seven years (A. D. 1066-1073) elapsed in which there was no inundation. A slight rise is sure to occasion dearth; and on the other hand a great flood, in addition to the usual disasters attending high waters, entails various infectious diseases, especially murrain and the plague. It thus happens that a variation of only a few feet in the annual overflow of the river produces the most important results.
From time immemorial the yearly prosperity of Egypt has been estimated by the periodic overflow of the Nile. At Er-Rodah, near Cairo, in Lower Egypt; at Memphis, a little further south; and at Thebes, graduated pillars, called Nilometers, register the height of the annual inundation, and from this the annual estimates are made.
The current of the Nile is sluggish, the average velocity being at low water more than two miles per hour, and during the flood not exceeding three or three and a-half miles. The water of the river differs greatly in appearance at different seasons of the year. During the inundation the stream is exceedingly turbid. Afterwards for about two weeks it assumes a greenish tinge, owing to the presence of large quantities of vegetable matter brought down from the tropics.
Again it takes the turbid appearance, and retains it during the period of subsidence, until the winter months, when the waters are comparatively clear. At all times, when not agitated, the earthy sediment is quickly deposited, and except during the green stage of the flood, the water is pure and sweet.
Egypt is the "Gift of the Nile"-so called from antiquity. As the waters of the annual overflow subside, a film of the richest alluvium is deposited over the whole valley. No artificial methods of renewing the soil can equal