PRISM (iplopa), in Mathematics, is a solid formed by a straight line which moves parallel to a given straight line, and one end of which traces out the contour of a given rectilinear polygon. The other extremity of the moving straight line traces out an equal and similar polygon, placed parallel to the former one : and the prism is thus bounded by two equal and parallel polygons, joined by as many parallelograms as cashpolygon him sides. When these parallelograms are at right angles to the planea of the polygons, the solid is called a right prism ; in all other cams, an oblique prism. The prism is among plane solids what the cylinder is among curvilinear ones : it is also called triangular, quadrangular, pentagonal, &c., according as have three, four, five, &c., sides. Thus the prism used in optics is a triangular prism, while the parallelopiped in a quadrangular prism.
The number of cubic unite in the contents of a prism is found by multiplying the number of square units in either of the polygons by the number of linear unite in the perpendicular distance between the planes of the two polygons; and all prisms, however much they may differ in obliquity, which have equal bases, and equal heighta or perpendicular distances between opposite polygons, are equal M mag nitude.
No other rule can be given for computing the surface of a prism except the simple direction to add the areas of the two polygons to those of the joining parallelograms. But in the case of a right prism, the finding of the parallelograms may be shortened by multiplying the number of linear units in the contour of one polygon by the altitude of the prism.