achromatic prism

2 definitions found

achromatic prism - Collaborative International Dictionary of English v.0.48 :

  Prism \Prism\ (pr[i^]z'm), n. [L. prisma, Gr. pri`sma, fr.
     pri`zein, pri`ein, to saw: cf. F. prisme.]
     1. (Geom.) A solid whose bases or ends are any similar,
        equal, and parallel plane figures, and whose sides are
        parallelograms.
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     Note: Prisms of different forms are often named from the
           figure of their bases; as, a triangular prism, a
           quadrangular prism, a rhombic prism, etc.
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     2. (Opt.) A transparent body, with usually three rectangular
        plane faces or sides, and two equal and parallel
        triangular ends or bases; -- used in experiments on
        refraction, dispersion, etc.
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     3. (Crystallog.) A form the planes of which are parallel to
        the vertical axis. See Form, n., 13.
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     Achromatic prism (Opt.), a prism composed usually of two
        prisms of different transparent substances which have
        unequal dispersive powers, as two different kinds of
        glass, especially flint glass and crown glass, the
        difference of dispersive power being compensated by giving
        them different refracting angles, so that, when placed
        together so as to have opposite relative positions, a ray
        of light passed through them is refracted or bent into a
        new position, but is free from color.
  
     Nicol's prism, Nicol prism. [So called from Wm. Nicol, of
        Edinburgh, who first proposed it.] (Opt.) An instrument
        for experiments in polarization, consisting of a rhomb of
        Iceland spar, which has been bisected obliquely at a
        certain angle, and the two parts again joined with
        transparent cement, so that the ordinary image produced by
        double refraction is thrown out of the field by total
        reflection from the internal cemented surface, and the
        extraordinary, or polarized, image alone is transmitted.
        [1913 Webster] Prismatic

  Achromatic \Ach`ro*mat"ic\, a. [Gr. 'achrw`matos colorless; 'a
     priv. + chrw^ma, chrw`matos, color: cf. F. achromatique.]
     1. (Opt.) Free from color; transmitting light without
        decomposing it into its primary colors.
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     2. (Biol.) Uncolored; not absorbing color from a fluid; --
        said of tissue.
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     Achromatic lens (Opt.), a lens composed usually of two
        separate lenses, a convex and concave, of substances
        having different refractive and dispersive powers, as
        crown and flint glass, with the curvatures so adjusted
        that the chromatic aberration produced by the one is
        corrected by other, and light emerges from the compound
        lens undecomposed.
  
     Achromatic prism. See Prism.
  
     Achromatic telescope, or microscope, one in which the
        chromatic aberration is corrected, usually by means of a
        compound or achromatic object glass, and which gives
        images free from extraneous color.
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