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OCR
98 LIGHT AND WATER projects into the shallow water. The brilliant colour here may be partly caused by the yellow or orange colour of the stone or shingle. A bank of pink sand seen through the blue water sometimes shows as a purplish streak, whilst the margin of deeper purple at the waters edge is due to masses of seaweed and ink-like stains on the submerged rocks. These pink or purple-blue patches on the water can be seen almost anywhere along our coasts. That rocks, which at low tide are seen to be of a dark purple colour, or even the darker kinds of seaweed, should give rise to such patches seems natural enough, but it may occasion some surprise to find that they are often caused by orange or olive-green seaweed. So different is the natural colour of the seaweed to the delicate “pink madder” colour that it assumes under water, that the casual observer will hardly connect the two, until he has satisfied himself on this point by closer inspection (see page 110). In very calm waters, dark lines, having almost the appearance of shadows, are often seen stretching across the surface in the distance; these will prove on approach to consist of minute ripples reflecting light from the upper sky. The water is seldom smooth enough to reflect the lowest region of the sky. Thus it is that the golden streak of light from the setting sun disappears before the sun touches the horizon. But if the sea is absolutely calm, the horizon line may entirely disappear—an effect said to be of common occurrence in the Mediterranean—so exactly is the colour of the sky repeated in the water. For we owe our usual horizon line to the fact that the ripples on
