The rainbow, that wonderfully beautiful bow of prismatic tints, which sometimes throws its ethereal arch across the heavens for a brief while, is caused by the reflection of the sun’s rays shining upon drops of rain, the colours being arranged in definite order; red, orange, yellow, green, blue, indigo and violet. The lunar rainbow, which occasionally forms at night when the moon shines, is not of frequent occurrence, but very beautiful when it does deign to show itself. Its colouring is not nearly as distinct at the rainbow, but ghostly, and of a pale-yellowish tint. Frequently a double rainbow is seen after a shower; this is but a reflection of the rainbow proper, but indescribably beautiful.
In the coming of the rainbow we have a Biblical symbol. It is spoken of in Genesis, and was used as a token of the Covenant; as a Divine promise to man, that the earth should never again be destroyed by flood.
There are numberless so-called signs, which are considered reliable indications of rain. Almost invariably a continuous south wind will, in most localities, bring in its wake rain in a few days. On the contrary, a continuous north wind is liable to dispel all rain signs for a time.
151. Thunder and hail storm type
152. From a great rain storm which lasted 15 hours
A “mackerel sky,” that is, a sky covered with a wide expanse of small silvery clouds, round in shape, is another rather sure indication of rain; salmon-coloured, leaden, or silvery clouds are usually indications of falling weather, and when at sunset the clouds of the west are brightly coloured, red or flame-coloured, afterwards followed by lighter hues, streaking up from the place where the sun disappeared, and stretching far across the sky, finally converging to a common point on the opposite horizon, you may be quite certain that somewhere within line of the sun, there is a heavy storm brewing; although it may be invisible, and hidden by the earth.
We know that in certain parts of the earth the rain seldom falls. In Lima (Peru), Thebes (Egypt), and in certain sections of North Africa they very rarely have rain. The presence of forests tends to increase the rainfall. Over the ocean it is always clear when the trade winds are blowing steadily, while rains fall continuously in the zone of calms.
Some countries are rarely free from rains; in Hindustan, Brazil and Guadeloupe the rain is almost continuous, while certain localities are noted for prolonged seasons of either drought or rain, which occur at stated periods, as in California.