DICT.TW Dictionary Taiwan

 Plane, n.
 1. Geom. A surface, real or imaginary, in which, if any two points are taken, the straight line which joins them lies wholly in that surface; or a surface, any section of which by a like surface is a straight line; a surface without curvature.
 2. Astron. An ideal surface, conceived as coinciding with, or containing, some designated astronomical line, circle, or other curve; as, the plane of an orbit; the plane of the ecliptic, or of the equator.
 3. Mech. A block or plate having a perfectly flat surface, used as a standard of flatness; a surface plate.
 4. Joinery A tool for smoothing boards or other surfaces of wood, for forming moldings, etc. It consists of a smooth-soled stock, usually of wood, from the under side or face of which projects slightly the steel cutting edge of a chisel, called the iron, which inclines backward, with an apperture in front for the escape of shavings; as, the jack plane; the smoothing plane; the molding plane, etc.
 Objective plane Surv., the horizontal plane upon which the object which is to be delineated, or whose place is to be determined, is supposed to stand.
 Perspective plane. See Perspective.
 Plane at infinity Geom., a plane in which points infinitely distant are conceived as situated.
 Plane iron, the cutting chisel of a joiner's plane.
 Plane of polarization. Opt. See Polarization.
 Plane of projection. (a) The plane on which the projection is made, corresponding to the perspective plane in perspective; -- called also principal plane. (b) Descriptive Geom. One of the planes to which points are referred for the purpose of determining their relative position in space.
 Plane of refraction or Plane of reflection Opt., the plane in which lie both the incident ray and the refracted or reflected ray.

 Prin·ci·pal a.
 1. Highest in rank, authority, character, importance, or degree; most considerable or important; chief; main; as, the principal officers of a Government; the principal men of a state; the principal productions of a country; the principal arguments in a case.
    Wisdom is the principal thing.   --Prov. iv. 7.
 2. Of or pertaining to a prince; princely. [A Latinism] [Obs.]
 Principal axis. See Axis of a curve, under Axis.
 Principal axes of a quadric Geom., three lines in which the principal planes of the solid intersect two and two, as in an ellipsoid.
 Principal challenge. Law See under Challenge.
 Principal plane. See Plane of projection (a), under Plane.
 Principal of a quadric Geom., three planes each of which is at right angles to the other two, and bisects all chords of the quadric perpendicular to the plane, as in an ellipsoid.
 Principal point Persp., the projection of the point of sight upon the plane of projection.
 Principal ray Persp., the line drawn through the point of sight perpendicular to the perspective plane.
 Principal section Crystallog., a plane passing through the optical axis of a crystal.