They are bent or turned from a straight course. What is said of these bent rays? They are said to be _refracted_. What is meant by refraction? Bending a ray of light, as it passes from one substance to another of different density; as from air to water, or from water to air. Where may we see an example of refraction? In the rays of light from a rod which has one end in the water. [Illustration: Fig. 7.] Why does the rod appear to be bent? Because light coming from the part of the rod under the water, is refracted or bent at the surface of the water, while the light from the part above the surface, comes in straight lines to the eye; hence, the rod appears to be bent at the surface, as is represented in Fig. 7. How does a pole appear when one end is placed in the water? It appears to be bent where it meets the surface of the water. How does the part of the rod under water appear? The part under the water appears to be raised up, as may be seen in Fig. 7. How does the bottom of a pond or stream of water appear? It appears to be raised up, and the water does not seem so deep as it really is. Why is this the case? Because the light from the bottom of the pond is refracted or bent at the surface of the water; hence, the bottom appears to be raised up. How much does the bottom of a pond or stream of water seem to be raised up? About one-third of the depth of the water. If the water is really six feet deep, how deep does it appear? It appears to be only four feet deep. What has frequently happened from not knowing this fact? People have been drowned from getting into water deeper than it appeared to be. Do the fish and other things floating in the water appear to be raised up? Yes; like the bottom of the stream, they also appear to be only two-thirds as far from the surface as they really are. If we wish to spear the fish, what must we do? We must aim below the place where they seem to be, or we must strike perpendicularly at them. Reflection of Light. When a ball is thrown against a wall, what is the path through which it goes called? The line of incidence. When the ball bounds back, what is its path called? The line of reflection. What is the angle at which a ball strikes the wall called? The angle of incidence. What is the angle at which the ball rebounds called? The angle of reflection. When a ray of light falls upon a looking-glass, what is the path through which it goes called? The line of incidence. When the ray is reflected, what is its path called? The line of reflection. The _angle of incidence_ is the angle between a perpendicular and the line of incidence; and the _angle of reflection_ is the angle between the perpendicular and the line of reflection. The two angles are always equal to each other, as is represented in Fig. 8. [Illustration: Fig. 8.] When a ray of light strikes a looking-glass obliquely or slantingly, what is done with it?