PRISM

In Geometry, a solid contained by p, nr.es of which two that are opposite are equal, similar, and parallel, and all the rest parallelograms. Prisms take particular names from the figures of their ends, or opposite equal and parallel sides. When the ends are triangles, they are called triangular prisms; when the ends are square, square prisms; when the ends are pentagonal, ]>ent agonal prisms; and so on. A ri^Ar. prism has its sides perpendicular to its ends; an oblique prism is that of which the sides are oblique to the ends. The solid content of a prism is found by multiplying the area of the base into the perpendicular altitude; hence all prisms are to one another in the ratio compounded of their bases and altitudes. Prism. In Dioptrics, a piece of gla or other diaphanous substancV, in form of a triangular prism, employed to separate a ray of light into its constituent pans or colours by refraction. The prism Is the instrument by means of which most of the remarkable phenomena of light and colours are exhibited. See CHROMATICS, OPTICS, REFRACTION. [s. 1001]