Archimedean Screw, an apparatus used for raising water. It consists of a screw blade turned around a solid axis, similar to a winding staircase, and enclosed in a hollow cylinder. When placed in an inclined position, with the lower end in water, the latter will be caught between the screw blades, and the cylinder being turned in the proper direction, the water will be raised and discharged at the upper end. Our first figure represents such an apparatus, with one half of the enclosing cylinder removed, so as to expose the interior arrangement and form of the screw blade. It is still occasionally used, when water is to be raised to a limited height of 10 to 15 feet or less, and the quantity is so large that a dozen pumps would be required; in this case an Archimedean screw turned by two or three men will economize greatly the labor, as with it each man is able to raise per minute 40 gallons of water 10 feet high, or in general to produce the labor of nearly 4,000 foot pounds per minute. This is a larger amount of work than generally can be done with pumps, in which the friction is always considerable when compared with that of the pivots on which the Archimedean screw turns.

If water is to be raised to great heights, however, say 90 or 100 feet, this apparatus is not practicable, and pumps are requisite. - Another form of this apparatus is represented in our second figure. It consists of a tube wound spirally around a core, and operates on the same principle as the former; but it has a much smaller capacity, and is therefore seldom used on a large scale for practical purposes.

Fig. 1. - Archimedean Screw with Spiral Blade.

Fig. 2. - Tubular Archimedean Screw.