Stranica 119 [119]
OCR
COLOURS IN STILL WATER 6s towards O. The ray OE would then consist of rays travelling along AO and CO, and—assuming the water to be still—of these rays alone. It is evident that only a minute fraction of the light from above reaches the eye, whilst it receives a very considerable proportion of the light from below the surface. On the other hand, by superimposing Figs. 25 (II) and (IV), we see that when the eye is placed at e, so that the line of vision, eO, strikes the surface of the water very obliquely, it receives a large amount of reflected, and only a small portion.of refracted, light. The significance of this point will soon be apparent. When light is reflected at the surface of water it is unchanged in colour, and therefore the " double” of the objects that we imagined inverted below the surface of the water in Chapter I, is similar to the real scene in colour, as well as in form, though, as our view of this image is a different one to our direct view of the objects, so we may get in the reflexion different combinations of colouring or different effects of light and shade (page 17). But besides the reflexions that we see on the water, we actually perceive in most cases and to a certain extent the colour of the water itself. Let us consider this apart from the reflexions. How do we get the sensation of colour? We know that by passing the sun's light through a prism it can be split up into rays of different wave-lengths, which produce upon the eye the effects of the different colours of the rainbow, and that these coloured rays can be reunited by means of a second prism to form white light again. So we say that white light is composed of light of all colours. Any transparent coloured F
