plate C is horizontal like A, the ray will be reflected from C ; but when the plate C, still preserving its inclination of 560, is turned round so as to be vertical, the ray will no longer be reflected, and will disappear.
The
ray after incidence on A is said to be polarized, the test of its
polarization being that it refuses to be reflected from C when C is at
a plane at right angles to the plane of incidence A.
The angle, 560, by
which light becomes polarized by incidence on glass is called the
polarizing angle. This angle is different for different bodies. The
diamond is about 68°. Light may also be polarized by transmission
through tourmaline, Iceland spar, or other double refracting bodies. To
determine the polarizing angle of a body, we have only to reflect a ray
of light from its surface at such an angle that it shall refuse to be
reflected by a plate of glass inclined at an angle of 560,
and placed in a plane at right angles to the first plane of reflection,
or that it shall incapable of transmission through a plate of tour-
