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Scientific American, Vol. 84, No. 3 (January 19, 1901) (1901)
leaf 4
The shutter described. After the felt has been put is placed horizontally (Fig. 1) against in place an outer layer of concrete the opening, F, behind which the film whose thickness is determined by the passes. In its revolution the shutter nature of the excavation is carefully presents its closed… … © 1901 SCIENTIFIC AMERICAN, INC.Internet Archive · Public domain (published before 1931). Free to use for anything.
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