Perspective glass

Perspective \Per*spec"tive\, n. [F. perspective, fr. perspectif:
   cf. It. perspettiva. See {Perspective}, a.]
   1. A glass through which objects are viewed. [Obs.] "Not a
      perspective, but a mirror." --Sir T. Browne.
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   2. That which is seen through an opening; a view; a vista.
      "The perspective of life." --Goldsmith.
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   3. The effect of distance upon the appearance of objects, by
      means of which the eye recognizes them as being at a more
      or less measurable distance. Hence, a["e]rial perspective,
      the assumed greater vagueness or uncertainty of outline in
      distant objects.
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            A["e]rial perspective is the expression of space by
            any means whatsoever, sharpness of edge, vividness
            of color, etc.                        --Ruskin.
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   4. The art and the science of so delineating objects that
      they shall seem to grow smaller as they recede from the
      eye; -- called also {linear perspective}.
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   5. A drawing in linear perspective.
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   {Isometrical perspective}, an inaccurate term for a
      mechanical way of representing objects in the direction of
      the diagonal of a cube.

   {Perspective glass}, a telescope which shows objects in the
      right position.
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