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ANN RONAN PICTURE LIBRARY / HERITAGE IMAGES / SCIENCE PHOTO LIBRARY ANN RONAN PICTURE LIBRARY / HERITAGE IMAGES / SCIENCE PHOTO LIBRARY
Archimedean Screws for raising water from one level to another. The 'thread' could be either external (as in Fig. 3), or the more conventional internal spiral in Fig. 2. From Ferguson's Lectures edited David Brewster, Edinburgh, 1805.
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