Part 378

Po"lack (?), n. A Polander. Shak.

Po*la"cre (?), n. Same as Polacca, 1.

Po"land*er (?), n. A native or inhabitant of Poland; a Pole.

Po"lar (?), a. [Cf. F. polaire. See Pole of the earth.] 1. Of or pertaining to one of the poles of the earth, or of a sphere; situated near, or proceeding from, one of the poles; as, polar regions; polar seas; polar winds.

2. Of or pertaining to the magnetic pole, or to the point to which the magnetic needle is directed.

3. (Geom.) Pertaining to, reckoned from, or having a common radiating point; as, polar coˆrdinates.

Polar axis, that axis of an astronomical instrument, as an equatorial, which is parallel to the earths axis. -- Polar bear (Zoˆl.), 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 spermatozoˆn; 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′, 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 coˆrdinates. See under 3d Coˆrdinate. -- 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 coˆrdinates 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 (Zoˆl.), 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 (Zoˆl.), the right whale, or bowhead. See Whale.

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Po"lar (?), n. (Conic Sections) The right line drawn through the two points of contact of the two tangents drawn from a given point to a given conic section. The given point is called the pole of the line. If the given point lies within the curve so that the two tangents become imaginary, there is still a real polar line which does not meet the curve, but which possesses other properties of the polar. Thus the focus and directrix are pole and polar. There are also poles and polar curves to curves of higher degree than the second, and poles and polar planes to surfaces of the second degree.

Pol"ar*chy (?), n. See Polyarchy.

Po*lar"ic (?), a. See Polar. [R.]

Po"lar*i*ly (?), adv. In a polary manner; with polarity. [R.] Sir T. Browne.

Po`lar*im"e*ter (?), n. [Polar + -meter.] (Opt.) An instrument for determining the amount of polarization of light, or the proportion of polarized light, in a partially polarized ray.

Po`lar*im"e*try (?), n. (Opt.) The art or process of measuring the polarization of light.

||Po*la"ris (?), n. [NL. See Polar.] (Astron.) The polestar. See North ||star, under North.

Po*lar"i*scope (?), n. [Polar + -scope.] (Opt.) An instrument consisting essentially of a polarizer and an analyzer, used for polarizing light, and analyzing its properties.

Po*lar`i*scop"ic (?), a. (Opt.) Of or pertaining to the polariscope; obtained by the use of a polariscope; as, polariscopic observations.

Po`lar*is"co*py (?), n. (Opt.) The art or rocess of making observations with the polariscope.

Po`lar*is"tic (?), a. Pertaining to, or exhibiting, poles; having a polar arrangement or disposition; arising from, or dependent upon, the possession of poles or polar characteristics; as, polaristic antagonism.

Po*lar"i*ty (?), n. [Cf. F. polaritÈ.] 1. (Physics) That quality or condition of a body in virtue of which it exhibits opposite, or contrasted, properties or powers, in opposite, or contrasted, parts or directions; or a condition giving rise to a contrast of properties corresponding to a contrast of positions, as, for example, attraction and repulsion in the opposite parts of a magnet, the dissimilar phenomena corresponding to the different sides of a polarized ray of light, etc.

2. (Geom.) A property of the conic sections by virtue of which a given point determines a corresponding right line and a given right line determines a corresponding point. See Polar, n.

Po"lar*i`za*ble (?), a. Susceptible of polarization.

Po`lar*i*za"tion (?), n. [Cf. F. polarisation.]

1. The act of polarizing; the state of being polarized, or of having polarity.

2. (Opt.) A peculiar affection or condition of the rays of light or heat, in consequence of which they exhibit different properties in different directions.

If a beam of light, which has been reflected from a plate of unsilvered glass at an angle of about 56∞, be received upon a second plate of glass similar to the former, and at the same angle of incidence, the light will be readily reflected when the two planes of incidence are parallel to each other, but will not be reflected when the two planes of incidence are perpendicular to each other. The light has, therefore, acquired new properties by reflection from the first plate of glass, and is called polarized light, while the modification which the light has experienced by this reflection is called polarization. The plane in which the beam of light is reflected from the first mirror is called the plane of polarization. The angle of polarization is the angle at which a beam of light must be reflected, in order that the polarization may be the most complete. The term polarization was derived from the theory of emission, and it was conceived that each luminous molecule has two poles analogous to the poles of a magnet; but this view is not now held. According to the undulatory theory, ordinary light is produced by vibrations transverse or perpendicular to the direction of the ray, and distributed as to show no distinction as to any particular direction. But when, by any means, these, vibrations are made to take place in one plane, the light is said to be plane polarized. If only a portion of the vibrations lie in one plane the ray is said to be partially polarized. Light may be polarized by several methods other than by reflection, as by refraction through most crystalline media, or by being transmitted obliquely through several plates of glass with parallel faces. If a beam of polarized light be transmitted through a crystal of quartz in the direction of its axis, the plane of polarization will be changed by an angle proportional to the thickness of the crystal. This phenomenon is called rotatory polarization. A beam of light reflected from a metallic surface, or from glass surfaces under certain peculiar conditions, acquires properties still more complex, its vibrations being no longer rectilinear, but circular, or elliptical. This phenomenon is called circular or elliptical polarization.

3. (Elec.) An effect produced upon the plates of a voltaic battery, or the electrodes in an electrolytic cell, by the deposition upon them of the gases liberated by the action of the current. It is chiefly due to the hydrogen, and results in an increase of the resistance, and the setting up of an opposing electro- motive force, both of which tend materially to weaken the current of the battery, or that passing through the cell.

Po"lar*ize (?), v. t. [imp. & p. p. Polarized (?); p. pr. & vb. n. Polarizing (?).] [Cf. F. polariser.] To communicate polarity to.