Tel·e·scope n.  An optical instrument used in viewing distant objects, as the heavenly bodies.
 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.
 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.
 Gre·go·ri·an a.  Pertaining to, or originated by, some person named Gregory, especially one of the popes of that name.
 Gregorian calendar, the calendar as reformed by Pope Gregory XIII. in 1582, including the method of adjusting the leap years so as to harmonize the civil year with the solar, and also the regulation of the time of Easter and the movable feasts by means of epochs. See Gregorian year (below).
 Gregorian chant Mus., plain song, or canto fermo, a kind of unisonous music, according to the eight celebrated church modes, as arranged and prescribed by Pope Gregory I. (called “the Great”) in the 6th century.
 Gregorian modes, the musical scales ordained by Pope Gregory the Great, and named after the ancient Greek scales, as Dorian, Lydian, etc.
 Gregorian telescope Opt., a form of reflecting telescope, named from Prof. James Gregory, of Edinburgh, who perfected it in 1663. A small concave mirror in the axis of this telescope, having its focus coincident with that of the large reflector, transmits the light received from the latter back through a hole in its center to the eyepiece placed behind it.
 Gregorian year, the year as now reckoned according to the Gregorian calendar. Thus, every year, of the current reckoning, which is divisible by 4, except those divisible by 100 and not by 400, has 366 days; all other years have 365 days. See Bissextile, and Note under Style, n., 7.
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 Gregorian telescope
      n : a reflecting telescope that has a paraboloidal primary
          mirror and a hyperboloidal secondary mirror; light is
          brought to a focus through an aperture in the center of
          the primary mirror [syn: Cassegrainian telescope]