and as far from the perpendicular as was the incident ray, as shown
at Fig. 2; a representing the incident ray and b the reflected.
The point, or angle c made by
[hipho_2.gif]
the incident ray, at the surface of the reflector e f, with a line c d,
perpendicular to that surface, is called the angle of incidence,
while the angle formed by the reflected ray b and the perpendicular line
d is called the angle of reflection, and these angles are always equal.

It is by this reflection of light that objects are made visible;
but unless light falls directly upon the eye they are invisible,
and are not sensibly felt until after a certain series of
operations upon the various coverings and humors of the eye.
Smooth and polished surfaces reflect light most powerfully,
and send to the eye the images of the objects from which the light
proceeded before reflection. Glass, which is transparent--
transmitting light--would be of no use to us as a mirror,
were it not first coated on one side with a metalic amalgam,
which interrupts the rays in their passage from the glass into
the air, and throws them either directly in the incident line,
or in an oblique direction. The reason why trees,
rocks and animals are not all mirrors, reflecting other forms
instead of their own, is, that their surfaces are uneven,
and rays of light reflected from an uneven surface are diffused
in all directions.

Parallel rays falling obliquely upon a plane mirror are reflected parallel;
converging rays, with the same degree of convergence; and diverging
rays equally divergent.