Stranica 162 [162]
OCR
96 LIGHT AND WATER It w ould be outside the scope of this essay to attempt to discuss fully and systematically the varied and complex colour effects seen at sea, but, beyond the general outline which wehavepresented, atewremarks on some special features will not be out of place. The waters of the Mediterranean are rich in colouring, and will furnish illustration of certain points. At some distance from land, the churning of the screw or the foam of the breakers shows an almost pure blue, but nearer shore (probably owing to contamination of some kind) the water assumes a greenish tinge, which becomes still more marked in the harbours. This brilliant colour, it need hardly be said, is Dover that often greets us on our return to English waters from sunnier seas. Looking down into the clear depths of the Mediterranean, however, the water often seems to be of a slightly purplish or violet blue, and does not show any sign of green. Even ona dull day, when looked at perpendicularly from the deck or in the near sides of the waves, it still appears of this beautiful deep ultramarine,—so that the colour is evidently not due to reflexion from the blue sky,— whilst the farther sides of the waves, being tilted away from us, reflect strongly the gray light from the clouds. The most probable explanation of this difference is that sea water, in common with many other liquids, possesses the property of showing a somewhat different colour according as one is looking through a thick or a thin layer of it." In this case the particles in the ‘ A solution of Prussian blue, with which the sea water was matched in Threlfall’s experiments, described on page 84, has this —_—_ tédöt ás áá eA
