Equatorial telescope

Telescope \Tel"e*scope\, n. [Gr. ? viewing afar, farseeing; ?
   far, far off + ? a watcher, akin to ? to view: cf. F.
   t['e]lescope. See {Telegraph}, and {-scope}.]
   An optical instrument used in viewing distant objects, as the
   heavenly bodies.
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   Note: A telescope assists the eye chiefly in two ways; first,
         by enlarging the visual angle under which a distant
         object is seen, and thus magnifying that object; and,
         secondly, by collecting, and conveying to the eye, a
         larger beam of light than would enter the naked organ,
         thus rendering objects distinct and visible which would
         otherwise be indistinct and or invisible. Its essential
         parts are the object glass, or concave mirror, which
         collects the beam of light, and forms an image of the
         object, and the eyeglass, which is a microscope, by
         which the image is magnified.
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   {Achromatic telescope}. See under {Achromatic}.

   {Aplanatic telescope}, a telescope having an aplanatic
      eyepiece.

   {Astronomical telescope}, a telescope which has a simple
      eyepiece so constructed or used as not to reverse the
      image formed by the object glass, and consequently
      exhibits objects inverted, which is not a hindrance in
      astronomical observations.

   {Cassegrainian telescope}, a reflecting telescope invented by
      Cassegrain, which differs from the Gregorian only in
      having the secondary speculum convex instead of concave,
      and placed nearer the large speculum. The Cassegrainian
      represents objects inverted; the Gregorian, in their
      natural position. The Melbourne telescope (see Illust.
      under {Reflecting telescope}, below) is a Cassegrainian
      telescope.

   {Dialytic telescope}. See under {Dialytic}.

   {Equatorial telescope}. See the Note under {Equatorial}.

   {Galilean telescope}, a refracting telescope in which the
      eyeglass is a concave instead of a convex lens, as in the
      common opera glass. This was the construction originally
      adopted by Galileo, the inventor of the instrument. It
      exhibits the objects erect, that is, in their natural
      positions.

   {Gregorian telescope}, a form of reflecting telescope. See
      under {Gregorian}.

   {Herschelian telescope}, a reflecting telescope of the form
      invented by Sir William Herschel, in which only one
      speculum is employed, by means of which an image of the
      object is formed near one side of the open end of the
      tube, and to this the eyeglass is applied directly.

   {Newtonian telescope}, a form of reflecting telescope. See
      under {Newtonian}.

   {Photographic telescope}, a telescope specially constructed
      to make photographs of the heavenly bodies.

   {Prism telescope}. See {Teinoscope}.

   {Reflecting telescope}, a telescope in which the image is
      formed by a speculum or mirror (or usually by two
      speculums, a large one at the lower end of the telescope,
      and the smaller one near the open end) instead of an
      object glass. See {Gregorian, Cassegrainian, Herschelian,
      & Newtonian, telescopes}, above.

   {Refracting telescope}, a telescope in which the image is
      formed by refraction through an object glass.

   {Telescope carp} (Zool.), the telescope fish.

   {Telescope fish} (Zool.), a monstrous variety of the goldfish
      having very protuberant eyes.

   {Telescope fly} (Zool.), any two-winged fly of the genus
      {Diopsis}, native of Africa and Asia. The telescope flies
      are remarkable for having the eyes raised on very long
      stalks.

   {Telescope shell} (Zool.), an elongated gastropod ({Cerithium
      telescopium}) having numerous flattened whorls.

   {Telescope sight} (Firearms), a slender telescope attached to
      the barrel, having cross wires in the eyepiece and used as
      a sight.

   {Terrestrial telescope}, a telescope whose eyepiece has one
      or two lenses more than the astronomical, for the purpose
      of inverting the image, and exhibiting objects erect.
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Equatorial \E`qua*to"ri*al\, n. (Astron.)
   An instrument consisting of a telescope so mounted as to have
   two axes of motion at right angles to each other, one of them
   parallel to the axis of the earth, and each carrying a
   graduated circle, the one for measuring declination, and the
   other right ascension, or the hour angle, so that the
   telescope may be directed, even in the daytime, to any star
   or other object whose right ascension and declination are
   known. The motion in right ascension is sometimes
   communicated by clockwork, so as to keep the object
   constantly in the field of the telescope. Called also an
   {equatorial telescope}.
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   Note: The term equatorial, or equatorial instrument, is
         sometimes applied to any astronomical instrument which
         has its principal axis of rotation parallel to the axis
         of the earth.
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