in Geometry, denotes a plain surface, or one that lies evenly between its bounding lines: and as a right line is the shortest extension from one point to another, so a plane surface is the shortest extension from one line to another.

In astronomy, conics, &c., the term plane is frequently used for an imaginary surface, supposed to cut and pass through solid bodies; and on this foundation is the whole doctrine of conic sections built. See ASTRO- NOMY, CONIC SECTIONS, &c.

In mechanics, planes are either horizontal, that is, parallel to the horizon, or inclined thereto. See ME- CHANICS.

The determining how far any given plane deviates from a horizontal line, makes the whole business of levelling. See the article LEVELLING.

In optics, the planes of reflection and refraction are those drawn through the incident and reflected or re- fracted rays. See OPTICS.

In perspective we meet with the perspective plane, which is supposed to be pellucid, and perpendicular to the horizon; the horizontal plane, supposed to pass through the spectator's eye, parallel to the horizon; the geometrical plane, likewise parallel to the horizon, wherein the object to be represented is supposed to be placed, &c. See PERSPECTIVE.

The plane of projection in the stereographic projec- tion of the sphere, is that on which the projection is made, corresponding to the perspective plane. See PRO- JECTION.

joinery, an edged tool or instrument for paring and shaving of wood smooth. It consists of a piece of wood very smooth at bottom, as a stock or shaft; in the midst of which is an aperture, through which a steel edge, or chisel, placed obliquely, passes; which, being very sharp, takes off the inequalities of the wood along which it slides.

PLANE-Tree, in Botany. See PLATANUS.