The influence of light on the colours of organized creation is well shown in the sea. Near the shores we find sea-weeds of the most beautiful hues, particularly on the rocks which are left dry by the tides; and the rich tints of the actiniæ, which inhabit shallow water, must have been often observed. The fishes which swim near the surface are also distinguished by the variety of their colours, whereas those which live at greater depths are grey, brown, or black. It has been found that after a certain depth, where the quantity of light is so reduced that a mere twilight prevails, the inhabitants of the ocean become nearly colourless. That the sun’s ray alone gives to plants the property of reflecting colour is proved by the process of blanching, or _etiolation_, produced by artificially excluding the light. By a triangular piece of glass--a prism,--we are enabled to resolve light into its ultimate rays. The white pencil of light which falls on the first surface of the prism is bent from its path, and coloured bands of different colours are obtained. These bands or rays observe a curious constancy in their positions: the red ray is always the least bent out of the straight path: the yellow class comes next in the order of refrangibility; and the blue are the most diverted from the vertex of the prism. The largest amount of illuminating power exists in the yellow ray, and it diminishes towards either end.[95] It is not uninteresting to observe something like the same variety of colour occurring at each end of the prismatic spectrum. The strict order in which the pure and mixed coloured rays present themselves is as follows:-- 1. The _extreme red_: a ray which can only be discovered when the eye is protected from the glare of the other rays by a cobalt blue glass, is of a crimson character--a mixture of the _red_ and the _blue_, red predominating.[96] 2. The _red_: the first ray visible under ordinary circumstances. 3. The _orange_: red passing into and combining with yellow. 4. The _yellow_: the most intensely luminous of the rays. 5. The _green_: the yellow passing into and blending with the blue. 6. The _blue_: in which the light very rapidly diminishes. 7. The _indigo_: the dark intensity of blue. 8. The _violet_: the _blue_ mingled again with the _red_--blue being in excess. 9. The _lavender grey_: a neutral tint, produced by the combination of the red, blue, and yellow rays, which is discovered most easily when the spectrum is thrown upon a sheet of turmeric paper. 10. The fluorescent rays: which are either a _pure silvery blue_ or a delicate _green_.