which leaves the candle will fall upon the mirror as _AB_ and will be
reflected as _BC_ (in such a way that the angle of reflection equals
the angle of incidence). If an observer stands at _C_, he will think
that the point _A_ of the candle is somewhere along the line _CB_
extended. Such a supposition would be justified from Section 102. But
the candle sends out light in all directions; one ray therefore will
strike the mirror as _AD_ and will be reflected as _DE_, and an
observer at _E_ will think that the point _A_ of the candle is
somewhere along the line _ED_. In order that both observers may be
correct, that is, in order that the light may seem to be in both these
directions, the image of the point _A_ must seem to be at the
intersection of the two lines. In a similar manner it can be shown
that every point of the image of the candle seems to be behind the
mirror.

[Illustration: FIG. 62.--The image is a duplicate of the object, but
appears to be behind the mirror.]

It can be shown by experiment that the distance of the image behind
the mirror is equal to the distance of the object in front of the
mirror.

106. Why Objects are Visible. If the beam of light falls upon a
sheet of paper, or upon a photograph, instead of upon a smooth
polished surface, no definite reflected ray will be seen, but a glare
will be produced by the scattering of the beam of light. The surface
of the paper or photograph is rough, and as a result, it scatters the
beam in every direction. It is hard for us to realize that a smooth
sheet of paper is by no means so smooth as it looks. It is rough
compared with a polished mirror. The law of reflection always holds,