\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.
Note: If a beam of light, which has been reflected from a
      plate of unsilvered glass at an angle of about 56[deg],
      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.