The dam is also more wonderful than the Pyramids in its construction. Old Cheops is built on the edge of the desert on a solid stone platform, and is little more than the piling of one stone upon another. For the Aswan Dam a trench a hundred feet wide and a hundred feet deep had to be excavated in the granite rock. This was bedded with concreted rubble to form the substructure upon which the masonry was raised. The dam itself contains more than a million tons of granite and about fifteen thousand tons of steel, and the calculations of the engineers are so exact that they know just how much every ounce of stone and steel will hold back. I have had some talks here with the engineer-in-chief of the dam, and am surprised at the wonderful intelligence bureau that has been created in connection with the control of the Nile. Its officials know the exact weight of the river at every hour of the day. They have telegraphic reports on what the Nile is doing in Abyssinia, in Central Africa, and in the Sudan. They have dispatches as to every great rain, and they know to a ton just how fast Lower Egypt is using the water, so they can tell how much or how little to let out for the farms. They even estimate the force of the sun on the water and know how much it drinks up every day. When the reservoir is full Old Sol takes a million and a half tons from it every twenty-four hours. They know what the evaporation is, not only at Aswan, but all along the great stream and throughout its swamps to its source in Lake Victoria. [Illustration: The gift of the Nile is not had without work. _Fellaheen_ too poor to own camels or bullocks lift the river water from level to level and pour it into the irrigation ditches.] [Illustration: The _fellaheen_ live in villages and go out to work on the farms. The average mud hut seldom contains more than one or two rooms and is at the mercy of thick clouds of dust from the road.] I am also amazed at the strength and delicacy of the machinery of this remarkable structure. The great sluice gates are each as high as a two-story house, and so wide that you could drive a hay wagon through them without touching the walls. They are cut right through the granite dam and are closed or opened by steel doors, which slide up and down inside the wall on rollers. Upon the top of the dam there are machines for moving these gates, so made that a child could operate them. They are equipped to be operated by electricity, but they are now worked by hand, and this mighty force, so tremendous that two billion horses would be required to move it, is now controlled at will by the muscular power of a single man.