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Knight's Mechanical Encyclopedia (ed. Knight) 2 0 Browse Search
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Knight's Mechanical Encyclopedia (ed. Knight), S. (search)
ns, optical character, nature of lens, etc., as green, blue, neutral tint, smoke color; double concave, double convex, periscopic, pebble. Periscopic glasses were invented by the eccentric Dr. Wollaston. The glasses are concavo-convex, and facilitate oblique vision. Spectacles are said to be of Asiatic origin, and are of great antiquity in China. A spectacle lens was discovered in the Stabian Street at Pompeii in 1854. Alhazen appears to have referred to them. Roger Bacon, in his Opus Major, writes: This instrument, a plano-convex glass or large segment of a sphere, is useful to old men and to those who have weak eyes, for they may see the smallest letters sufficiently magnified. Bacon was born at Ilchester, in Somersetshire, in 1214, the year before the signing of Magna Charta; was educated at Oxford, then studied in Paris, where he took his degree, which was subsequently confirmed by the Oxford University; in 1240 he took the vows of a Franciscan at Oxford. His talents a