Oldal 130 [130]
OCR
72 LIGHT AND WATER from beneath the surface, which latter, proceeding in this case not from the bottom, but from particles floating in the water, give merely a general impression of its “local colour;” and, as before, the more obliquely we look upon the water, the more the former picture gains in strength at the expense of the latter. So that we have this further and more important condition governing the apparent colour of water. Given smooth water of a definite colour, with a fixed proportion of suspended particles, and illuminated toa certain degree, the apparent strength of colour depends upon the position of the observer, being greatest on lookong vertically down at the surface and lessening gradually as the line of vision strikes the surface more and more obliquely, the colour due to reflexion gaining in brilliancy as the local colour dies away. For instance, when looking very obliquely at a sheet of water in the distance, the objects beyond are reflected as in a mirror, the reflexions being practically identical in colour with the objects themselves, whilst the water itself appears perfectly colourless.’ Indeed it might be turned into blood and we should not perceive the change. The same phenomenon can be observed in any flat reflecting surface, such as the top of a wellpolished table. Sitting in a low chair, with the eye only slightly above the level of the table, one sees the objects beyond distinctly reflected, and one could not ! On referring to the table in the Note, page 64, it will be seen that at very oblique incidence water reflects by far the greater part of the light that falls upon it. At the same time the amount of refracted light reaching the eye in this position is so small as to be negligible.
