however, no matter what the reflecting surface is,--the angle of
reflection always equals the angle of incidence. In a smooth body the
reflected beams are all parallel; in a rough body, the reflected beams
are inclined to each other in all sorts of ways, and no two beams
leave the paper in exactly the same direction.

[Illustration: FIG. 63.--The surface of the paper, although smooth in
appearance, is in reality rough, and scatters the light in every
direction.]

Hot coals, red-hot stoves, gas flames, and candles shine by their own
light, and are self-luminous. Objects like chairs, tables, carpets,
have no light within themselves and are visible only when they receive
light from a luminous source and reflect that light. We know that
these objects are not self-luminous, because they are not visible at
night unless a lamp or gas is burning. When light from any luminous
object falls upon books, desks, or dishes, it meets rough surfaces,
and hence undergoes diffuse reflection, and is scattered irregularly
in all directions. No matter where the eye is, some reflected rays
enter it, and the various objects are clearly seen.




CHAPTER XI

REFRACTION


107. Bent Rays of Light. A straw in a glass of lemonade seems to be