Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. An indicator or a sighting apparatus on a plane table, used in angular measurement.
  • n. A topographic surveying and mapping instrument used for determining directions, consisting of a telescope and attached parts.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. A sighting device used for measuring angles.

from the GNU version of the Collaborative International Dictionary of English

  • n. The portion of a graduated instrument, as a quadrant or astrolabe, carrying the sights or telescope, and showing the degrees cut off on the arc of the instrument.

from The Century Dictionary and Cyclopedia

  • n. A movable arm passing over a graduated circle, and carrying a vernier or an index: an attachment of many instruments for measuring angles. See cut under sextant.
  • n. A straight-edge carrying a telescope: an attachment of the plane-table for transferring to paper the direction of any object from the station occupied.
  • n. Also written alhidade.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. surveying instrument consisting of the upper movable part of a theodolite including the telescope and its attachments
  • n. surveying instrument used with a plane table for drawing lines of sight on a distant object and for measuring angles

Etymologies

French, from Medieval Latin alidada, sighting rod, from Arabic al-'iḍāda, the revolving radius of a circle : al-, the + 'iḍāda, revolving radius (alternate form of 'aḍud, humerus, from 'aḍada, to lop, cut (trees); see ʿṢ́d in Semitic roots).
(American Heritage® Dictionary of the English Language, Fourth Edition)
From French alidade, from Spanish alidada, from Arabic عِضَادة, perhaps from عضد "upper arm". (Wiktionary)

Examples

  • The alidade is a triangular ruler with one or more working scales on it beside other measurements.

    Military Instructors Manual

  • Surveyors would place an alidade on the plane table and sight along it to a particular object, then draw a line to indicate the bearing.

    Book review: Thunderer by Felix Gilman

  • The mariner sighted the objects along a rule called an alidade.

    Book review: Thunderer by Felix Gilman

  • And then our trademark and exclusive, shipwreck artifacts: This time we will have a genuine bronze astrolabe, the most complete and intact one we have ever handled, fully dated 1656 and well detailed, solid and stable, alidade intact, one of fewer than 80 pieces known and among the best from any wreck.

    Daniel Frank Sedwick Treasure and World Coin Auction #7 : Coin Collecting News

  • Daddy was first attracted to seismic work because while in the Air Corps during World War II he had worked with an alidade and a transit -- in other words, it was the tools that drew him into what he would do for the rest of his life.

    HAROLD DERWIN BARNETT, 22 May 1925 - 16 October 2006

  • His foot caught on it in mid-leap, and he stumbled out onto the bridge wing, fetching up against the alidade.

    Nuke Zone

  • "Suraklin thought like that, you know," he said, making a minute adjustment to the rete and sighting along the alidade at the North Star, high in the frosty sky.

    The Silicon Mage

  • We find here the meridian circle, M, and the equator E, of the diagram shown in Fig. 3 (No. 4); but the circle with alidade is here replaced by a small aperture movable in a slide that is placed in

    Scientific American Supplement, No. 810, July 11, 1891

  • The line, a1 a2, that joins these axes is parallel with that which joins the axes of the two telescopes; and the alidades are connected electrically with the telescopes by a system such that each alidade always moves parallel with the telescope that corresponds to it.

    Scientific American Supplement, No. 363, December 16, 1882

  • One of the telescopes is then placed over its alidade and moves with it; and the apparatus thus comprehends only a system of synchronous movements.

    Scientific American Supplement, No. 363, December 16, 1882

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