Page 135 [135]
OCR
COLOURS IN STILL WATER . 7: is, however, very obvious in a case like that shown in the accompanying photograph of boats, taken from the high edge of the quay at low tide (Plate XAXAXAIII). Inthe reflexions of the first row of boats the dirty green of the water is far more apparent than in the reflexions of the second row, so much so that the bright stripes of paint on the nearer boats are almost lost, whilst those on the boats beyond are distinctly reproduced. Plate XX XIV is a further illustration of the same point. In this case the colour of the water could be plainly seen in the reflexion of the nearest duck, whilst that of the farthest showed no sign of it, but looked as white as the duck itself. It need scarcely be pointed out that, speaking generally, the “value” of water in the foreground, the reflected ray is much stronger than the refracted. By rough experiment the strengths of the reflected and refracted rays are found to be equal when looking at an angle of about 13° or 14° with the surface. If we mix into the water some Prussian blue or other pigment, we see its colour by means of light (reflected from the bottom of the basin) which has lost certain rays by absorption during its passage through the blue water, but, on lowering the eye to the second position, the colour of the water entirely disappears, and we see nothing but the reflexion of the white edge of the basin. We may now vary the first experiment as follows:—take a piece of bright red paper and hold it upright with its lower edge almost touching the water on the further side of the basin. The reflexion of this red paper as seen from the second position is almost identical in colour and strength with the direct view of it, but, on slowly raising the head, the blue colour of the water becomes more and more apparent, until, looking abruptly down on to the surface of the water, the red has almost entirely disappeared; so that the reflexion of the red paper seems to change from red through purple to blue, (See also footnotes, pages 79 and 92.)
