The length of the Nile is about three thousand three hundred miles, if we measure its wandering course from its exit at the lake to its entrance at the sea.
It is a remarkable fact that from the point where the last tributary enters the Nile, a distance of some fifteen hundred miles from the sea, no other waters are received to increase its volume; yet, in spite of this, the stream is able to withstand the scorching sun and burning sands of the Nubian Desert.
Little wonder, then, that the ancient Egyptians held the river sacred. To its influence they owed not only life, health, and strength, but their prosperity and wealth, as well.
Year after year they watched its annual overflow, rejoicing in this blessing of the waters.
At Khartoom the overflow begins in April. Lower Egypt does not become affected by the overflow of the waters till the latter part of June. Here the inundation does not attain its full height for about three months. The waters remain stationary for about twelve days, and then very gradually begin to subside.
The cultivation of the soil of entire Egypt is wholly dependent upon its inundation by the waters of the Nile. Its failure would mean drought and a total destruction of the crops, since Egypt is, practically, a rainless country.
Should there be a continuous wind from the south, then Egypt would be blessed by a year of prosperity. Should there be a continuous wind from the north, it would mean disaster to the country.
During a good inundation, the rise in the waters varies from forty feet, about the Tropic of Capricorn, to thirty-six feet at Thebes. Near the delta it is but four feet.
If, at Cairo, the waters rise to only eighteen or twenty feet, there is a scarcity of water. Should it rise to even twenty-four feet, there is still a deficiency. From twenty-five to twenty-seven feet is counted good for the welfare of the crops. More of an overflow would cause a flood. This would not only be productive, most likely, of plague and fever, but loss of crops and famine would follow in their wake.
During the months of inundation the whole valley is under water. Here and there the villages rise like islands from the surface of the waters.