# POLYHEDRON

, or Polyedron, a body or solid contained by many rectilinear planes or sides.

When the sides of the Polyhedron are regular polygons,
all similar and equal, then the Polyhedron becomes
a regular body, and may be inscribed in a sphere;
that is, a sphere may be described about it, so that its
surface shall touch all the angles or corners of the solid.
There are but five of these regular bodies, viz, the tetraedron,
the hexaedron or cube, the octaedron, the
dodecaedron, and the icosaedron. See Regular *Body,*
and each of those five bodies severally.

*Gnomonical* Polyhedron, is a stone with several
faces, on which are projected various kinds of dials.
Of this sort, that in the Privy-garden, London, now
gone to ruin, was esteemed the sinest in the world.

, in Optics. See Polyscope.

POLYHEDROUS *Figure,* in Geometry, a solid
contained under many sides or planes. See POLYHEDRON.