\Ste"re*o*scope\, n. [Stereo- + -scope.]
An optical instrument for giving to pictures the appearance
of solid forms, as seen in nature. It combines in one,
through a bending of the rays of light, two pictures, taken
for the purpose from points of view a little way apart. It is
furnished with two eyeglasses, and by refraction or
reflection the pictures are superimposed, so as to appear as
one to the observer.
Note: In the reflecting stereoscope, the rays from the two
      pictures are turned into the proper direction for
      stereoscopic vision by two plane mirrors set at an
      angle with each other, and between the pictures. In the
      lenticular stereoscope, the form in general use, the
      eyeglasses are semilenses, or marginal portions of the
      same convex lenses, set with their edges toward each
      other, so that they deflect the rays coming from the
      picture so as to strike the eyes as if coming direct
      from an intermediate point, where the two pictures are
      seen apparently as one.