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[[Image:arch screw 2.jpg|thumb|right|200px|An Egyptian farmer turning an Archimedes screw by hand to irrigate a field. [https://www.cs.drexel.edu/~crorres/Archimedes/Screw/Applications.html Photo:] Helen and Frank Schreider of the National Geographic staff.]]

The Archimedes Screw is basically a large helix, open at both ends and encased within a watertight cylinder. It operates with the cylinder somewhat tilted from vertical. When the open lower end of the cylinder is placed in water and the screw is turned, water trapped between the cylinder and the threads of the screw rises. Successive revolutions will raise the water thread-by-thread until it emerges at the top of the cylinder.