1911 Encyclopædia Britannica/Pole

POLE (1) (O. Eng. pál, cf. Ger. Pfahl, Du. paal, from Lat. palus, stake), a tapering cylindrical post or stake of some considerable length, used as a support in scaffolding, for telegraph or telephone wires, hops, &c., and as a means for taking jumps (see Pole-Vaulting), and also as a single shaft for a vehicle drawn by two or more horses. As a measure of length a “pole,” also called “rod” or “perch,” is equal to 51/2 yds. (161/2 ft.), as a measure of area it is equal to 301/4 sq. yds. (2) (Lat. polus, adapted from Gr. πόλος, pivot, axis). one or other of the extremities of the axis of the earth; the “celestial pole” is one or other of the points in the heavens to which the earth’s axis points; in the northern hemisphere this point is near the star Ursae minoris, better known as the Pole-star or Polaris (see Ursa Major). For the regions lying about the north and south poles of the earth see Polar Regions.

In mathematics the word pole has several meanings. In spherical trigonometry the “pole” of a circle on a sphere is the point where the diameter of the sphere perpendicular to the plane of the circle intersects the sphere. In crystallography (q.v) the “ pole" of a face is the intersection of a line perpendicular to the face with the sphere of projection. The term is also applied to a point from which lines radiate, as, for instance, the origin in a system of polar co-ordinates, or the common point of a pencil of rays. In the geometry of conic sections the “pole” of a line, termed the “polar” of the point, is the intersection of the tangents (either real or imaginary) at the points where the line meets the conic (see Geometry: § Projective). The “magnetic poles” of the earth are the points on the earth’s surface where the dipping needle is vertical (see Terrestrial Magnetism), and the “poles” of a magnet are the points of the magnet where the magnetic intensity is greatest. In electricity, the term is applied to the elements of a galvanic battery (q.v.), or to the terminals of a frictional electrical machine.