496. Why are haloes sometimes large and at other times small?
Because they are sometimes formed very high in the atmosphere, at other times very low. Being high, and farther removed from the spectator, and nearer the source of light, they appear smaller; while the nearer they are, the larger they appear.
497. Why do haloes foretell wet weather?
Because they show that there is a great amount of atmospheric moisture, which will probably form rain.
498. Why do glass lustres and chandeliers exhibit "rainbow colours"?
Because they refract the rays of light in the same manner as the rain drops.
499. Why does a soap bubble show the prismatic colours?
Because, like a large rain drop, it refracts the rays of light, and shows the elementary rays.
500. What causes the rich tints displayed by "mother-of-pearl?"
The refraction of the light that falls upon the surface of the pearl.