Source : Webster's Revised Unabridged Dictionary (1913)

   {Optically active}, {Optically inactive} (Chem. Physics),
      terms used of certain metameric substances which, while
      identical with each other in other respects, differ in
      this, viz., that they do or do not produce right-handed or
      left-handed circular polarization of light.

   {Optically positive}, {Optically negative}. See under
      {Refraction}.