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OCR
COLOURS IN RIPPLED WATER 97 depths give a thick layer, whilst the air bubbles in the wake, being near the surface, furnish a thin layer of water; the former appears violet-blue or ultramarine, the latter greenish or cyan-blue. When at anchor in full sunshine, the colour of the water is most vividly seen towards midday if the observer looks over the rail at the sunlit surface close to his own shadow, for in this position he is looking straight at the illuminated sides of the floating particles (as we do at the illuminated surface of the moon when at the full), and they therefore reflect more light to the eye than if the direction of vision differed considerably from that of illumination. Here the colour will be more brilliant than in the shadow of the vessel, where (as explained in the last chapter, page 77) more of the sky colour and less local colour is seen. Looking over the other side of the boat, the colour will not show up so strongly—unless in the dark reflexion of a boat lying alongside, where, the sky reflexion being interrupted, the colour of the water is again very obvious. bj By the shore there will often be seen a patch of bright green, where a shelving rock or pebbly beach property. If two bottles of colourless glass, one large and the other small, be filled from the same solution of Prussian blue, and placed against the same white background, the difference, not merely in shade, but actually in colour, between a thin and a thick layer of the solution will be seen at once. Indeed, one bottle is sufficient to show it, the colour varying with the direction in which one looks through the bottle, or with the strength of the transmitted light. The paler parts are distinctly green, the darker show no signs of it; and in the deepest parts, as when looking down on to the shoulder of the bottle, the violet tinge appears. H
