, or Dioptra, the same with the index or alhidade of an astrolabe, or other such instrument.
DIOPTRA was an instrument invented by Hipparchus, which served for several uses; as, to level water-courses; to take the height of towers, or places at a distance; to determine the places, magnitudes, and distances of the planets, &c.
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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.
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