[Verse: "I am come a light into the world, that whosoever believeth in me should not abide in darkness."--JOHN XIII.] 493. _Why is the lunar rainbow fainter than a solar rainbow?_ Because the _light of the moon_ is the _reflected light of the sun_, and is therefore _less intense_. 494. _What is a halo?_ A halo is a _luminous ring_, which forms between the eye of the observer and a luminous body. Haloes may appear around the disc of the sun, moon, or stars. But in this country the _lunar_ haloes are the most remarkable and frequent. 495. _What is the cause of the luminous ring?_ The _refraction of light_ as it passes through an intervening _cloud_, or a stratum of _moist_ and _cold air_. 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. [Verse: "Light is sown for the righteous, and gladness for the upright in heart."--PSALM XCVII.] 501. _What causes the brilliant colours of the diamond?_ The _refraction_ of the rays of light by the various _facets_ of the diamond.