smaller than the angle of incidence. When a ray of light passes from
water or glass into air, the refracted ray is bent away from the
perpendicular so that the angle of refraction is greater than the
angle of incidence.

The bending or deviation of light in its passage from one substance to
another is called refraction.

108. How Refraction Deceives us. Refraction is the source of many
illusions; bent rays of light make objects appear where they really
are not. A fish at _A_ (Fig. 66) seems to be at _B_. The end of the
stick in Figure 64 seems to be nearer the surface of the water than it
really is.

[Illustration: FIG. 66.--A fish at _A_ seems to be at _B_.]

The light from the sun, moon, and stars can reach us only by passing
through the atmosphere, but in Section 76, we learned that the
atmosphere varies in density from level to level; hence all the light
which travels through the atmosphere is constantly deviated from its
original path, and before the light reaches the eye it has undergone
many changes in direction. Now we learned in Section 102, that the
direction of the rays of light as they enter the eye determines the
direction in which an object is seen; hence the sun, moon, and stars
seem to be along the lines which enter the eye, although in reality
they are not.

109. Uses of Refraction. If it were not for refraction, or the
deviation of light in its passage from medium to medium, the wonders
and beauties of the magic lantern and the camera would be unknown to