Worthen, William Ezra, 1819-1897, [from old catalog] ed · New York, Appleton · leaf 535
Fig. 1241. The stones forming the arch are called votissoirs, or arch-stones; those form-ing the exterior face are called ring-stones, the inner line of arch the intrados,exterior line the extrados. The stones at the top, which are those set last andcomplete the arch, are keystones. The courses…
Mechanical drawing
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