n. [ Pref. bi- + prism. ] 1. A prism whose refracting angle is very nearly 180 degrees. [ Webster 1913 Suppl. ]

2. A combination of two short rectangular glass prisms cemented together at their diagonal faces so as to form a cube; -- called also optical cube. It is used in one form of photometer. [ Webster 1913 Suppl. ]

a. [ Prefix di- + prismatic. ] Doubly prismatic. [ 1913 Webster ]

n. [ Macro- + prism. ] (Crystallog.) A prism of an orthorhombic crystal between the macropinacoid and the unit prism; the corresponding pyramids are called macropyramids. [ 1913 Webster ]

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. [ 1913 Webster ]

☞ Prisms of different forms are often named from the figure of their bases; as, a triangular prism, a quadrangular prism, a rhombic prism, etc. [ 1913 Webster ]

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. [ 1913 Webster ]

3. (Crystallog.) A form the planes of which are parallel to the vertical axis. See Form, n., 13. [ 1913 Webster ]

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 ]

{ } a. [ Cf. F. prismatique. ] 1. Resembling, or pertaining to, a prism; as, a prismatic form or cleavage. [ 1913 Webster ]

2. Separated or distributed by a prism; formed by a prism; as, prismatic colors. [ 1913 Webster ]

3. (Crystallog.) Same as Orthorhombic. [ 1913 Webster ]

Prismatic borax (Chem.), borax crystallized in the form of oblique prisms, with ten molecules of water; -- distinguished from octahedral borax. --
Prismatic colors (Opt.), the seven colors into which light is resolved when passed through a prism; primary colors. See Primary colors, under Color. --
Prismatic compass (Surv.), a compass having a prism for viewing a distant object and the compass card at the same time. --
Prismatic spectrum (Opt.), the spectrum produced by the passage of light through a prism. [ 1913 Webster ]

adv. In the form or manner of a prism; by means of a prism. [ 1913 Webster ]

a. [ Gr. &unr_;, &unr_;, prism + -oid: F. prismatoïde. ] Having a prismlike form. Ure. [ 1913 Webster ]

. Glass with one side smooth and the other side formed into sharp-edged ridges so as to reflect the light that passes through, used at windows to throw the light into the interior. [ Webster 1913 Suppl. ]

n. [ Cf. F. prismtoïde. ] A body that approaches to the form of a prism. [ 1913 Webster ]

a. Having the form of a prismoid; as, prismoidal solids. [ 1913 Webster ]

a. Pertaining to a prism. [ R. ] [ 1913 Webster ]