Yet these non-luminous bodies can send out light if they are lighted up by some self-luminous body. It is well that this is so, or else we could never see anything that was not in itself giving out light.
If you will hold an apple or a stone in your hand and let the light of a candle or the Sun fall on it you will be able to see the apple or stone, and, although you will hardly be able to notice it, you will see them by the light which strikes them and is turned back, or reflected from their surfaces, as shown in [Fig. 141].
If a rubber ball is thrown on the sidewalk it will bounce back and this is just the way light acts when it strikes most objects—it bounces back, or, to use the right word, it is reflected.
When we look at the surface of the Earth by daylight we see the sand and stones, grass and trees, houses and other objects by the light which is reflected, or thrown back from the surface of these things by the Sun.
When we look at the surface of the Earth by the light of the Moon we also see the objects by reflected light, but in this case the light is twice reflected, for moonlight is the light of the Sun falling on the Moon and which is then reflected to the Earth, where it is again reflected to our eyes from the objects it falls on. This is the reason moonlight is so pale when compared with sunlight.
Fig. 141.—Light Reflected
by an Apple.
Fig. 142.—Light Refracted. Spoon
in Glass of Water.
Refraction of Light.—When a beam of light passes through glass, water and other transparent substances, and is bent out of a straight line it is said to be refracted.