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e earth, and indicating the hour of the day on an hour circle, by being turned toward the plane of maximum polarization of the light of the sky, which is always 90º from the sun. -- Polar coördinates. See under 3d Coördinate. -- Polar dial, a dial whose plane is parallel to a great circle passing through the poles of…

ce of a great circle; or the point in which a diameter of the sphere perpendicular to the plane of such circle meets the surface. Such a point is called the pole of that circle; as, the pole of the horizon; the pole of the ecliptic; the pole of a given meridian.

A plane figure having many angles, and consequently many sides; esp., one whose perimeter consists of more than four sides; any figure having many angles. Polygon of forces (Mech.), a polygonal figure, the sides of which, taken successively, represent, in length and direction, several forces acting simultaneously upon…

Having many sides, as a solid body. Polyhedral angle, an angle bounded by three or more plane angles having a common vertex.

A body or solid contained by many sides or planes.

Obs.] Portal bracing (Bridge Building), a combination of struts and ties which lie in the plane of the inclined braces at a portal, serving to transfer wind pressure from the upper parts of the trusses to an abutment or pier of the bridge.

act of going before, or forward. Lunisolar precession. (Astron.) See under Lunisolar. -- Planetary precession, that part of the precession of the equinoxes which depends on the action of the planets alone. -- Precession of the equinoxes (Astron.), the slow backward motion of the equinoctial points along the ecliptic,…

The superior influence of a planet. Shak.

First in dignity or importance; chief; principal; as, primary planets; a matter of primary importance.

s of the horizon. -- Prime-vertical dial, a dial in which the shadow is projected on the plane of the prime vertical. -- Prime-vertical transit instrument, a transit instrument the telescope of which revolves in the plane of the prime vertical, -- used for observing the transit of stars over this circle.…

(Spherical Projection), the circle cut from the sphere to be projected, by the primitive plane. -- Primitive colors (Paint.), primary colors. See under Color. -- Primitive Fathers (Eccl.), the acknowledged Christian writers who flourished before the Council of Nice, A. D. 325. Shipley. -- Primitive groove (Anat.),…

se, the motion of which was supposed to carry with it all the inclosed spheres with their planets in a daily revolution from east to west. See Crystalline heavens, under Crystalline. The motions of the greatest persons in a government ought to be, as the motions of the planets, under primum mobile. Bacon.…

, 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 eac…

A solid whose bases or ends are any similar, equal, and parallel plane figures, and whose sides are parallelograms.

d the like; -- sometimes with on, upon, into, etc.; as, to project a line or point upon a plane. See Projection, 4.

mething; delineation; plan; especially, the representation of any object on a perspective plane, or such a delineation as would result were the chief points of the object thrown forward upon the plane, each in the direction of a line drawn through it from a given point of sight, or central point; as, the projection of…

A solid figure contained by a plane rectilineal figure as base and several triangles which have a common vertex and whose bases are sides of the base.

rean proposition (Geom.), the theorem that the square described upon the hypothenuse of a plane right-angled triangle is equal to the sum of the squares described upon the other two sides. -- Pythagorean system (Astron.), the commonly received system of astronomy, first taught by Pythagoras, and afterward revived by C…

A plane figure having four angles, and consequently four sides; any figure having four angles.

One of the four parts into which a plane is divided by the coördinate axes. The upper right-hand part is the first quadrant; the upper left-hand part the second; the lower left-hand part the third; and the lower right-hand part the fourth quadrant.