Polar axis, that axis of an astronomical instrument, as an equatorial, which is parallel to the earths axis. -- Polar bear (Zoöl.), a large bear (Ursus, or Thalarctos, maritimus) inhabiting the arctic regions. It sometimes measures nearly nine feet in length and weighs 1,600 pounds. It is partially amphibious, very powerful, and the most carnivorous of all the bears. The fur is white, tinged with yellow. Called also White bear. See Bear. -- Polar body, cell, or globule (Biol.), a minute cell which separates by karyokinesis from the ovum during its maturation. In the maturation of ordinary ova two polar bodies are formed, but in parthogenetic ova only one. The first polar body formed is usually larger than the second one, and often divides into two after its separation from the ovum. Each of the polar bodies removes maternal chromatin from the ovum to make room for the chromatin of the fertilizing spermatozoön; but their functions are not fully understood. -- Polar circles (Astron. *** Geog.), two circles, each at a distance from a pole of the earth equal to the obliquity of the ecliptic, or about 23°] 28***prime], the northern called the arctic circle, and the southern the antarctic circle. -- Polar clock, a tube, containing a polarizing apparatus, turning on an axis parallel to that of the 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 90° 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 the earth. Math. Dict. -- Polar distance, the angular distance of any point on a sphere from one of its poles, particularly of a heavenly body from the north pole of the heavens. -- Polar equation of a line or surface, an equation which expresses the relation between the polar coördinates of every point of the line or surface. -- Polar forces (Physics), forces that are developed and act in pairs, with opposite tendencies or properties in the two elements, as magnetism, electricity, etc. -- Polar hare (Zoöl.), a large hare of Arctic America (Lepus arcticus), which turns pure white in winter. It is probably a variety of the common European hare (L. timidus). -- Polar lights, the aurora borealis or australis. -- Polar, or Polaric, opposition or contrast (Logic), an opposition or contrast made by the existence of two opposite conceptions which are the extremes in a species, as white and black in colors; hence, as great an opposition or contrast as possible. -- Polar projection. See under Projection. -- Polar spherical triangle (Spherics), a spherical triangle whose three angular points are poles of the sides of a given triangle. See 4th Pole, 2. -- Polar whale (Zoöl.), the right whale, or bowhead. See Whale.