If a body sends back white light unchanged, it appears white; if the surface has the property of altering the vibration to that degree which is calculated to produce redness, the result is a red colour: the annihilation of the undulations produces blackness. By the other view, or the corpuscular hypothesis, the beam of white light is supposed to consist of certain coloured rays, each of which has physical properties peculiar to itself, and thus is capable of producing different physiological effects. These rays falling upon a transparent or an opaque body suffer more or less absorption, and being thus dissevered, we have the effect of colour. A red body absorbs all the rays but the red; a blue surface, all but the blue; a yellow, all but the yellow; and a black surface absorbs the whole of the light which falls upon it. That natural colours are the result of white light, and not innate properties of the bodies themselves, is most conclusively shown by placing coloured bodies in monochromatic light of another kind, when they will appear either of the colour of that light, or, by absorbing it, become black; whereas, when placed in light of their own character, the intensity of colour is greatly increasing. Every surface has, therefore, a peculiar constitution, by which it gives rise to the diversified hues of nature. The rich and lively green, which so abundantly overspreads the surface of the earth, the varied colours of the flowers, and the numberless tints of animals, together with all those of the productions of the mineral kingdom, and of the artificial combinations of chemical manufacture, result from powers by which the relations of matter to light are rendered permanent, until its physical conditions undergo some change. There is a remarkable correspondence between the geographical position of a region and the colours of its plants and animals. Within the tropics, where “The sun shines for ever unchangeably bright,” the darkest green prevails over the leaves of plants; the flowers and fruits are tinctured with colours of the deepest dye, whilst the plumage of the birds is of the most variegated description and of the richest hues. In the people also of these climes there is manifested a desire for the most striking colours, and their dresses have all a distinguishing character, not of shape merely, but of chromatic arrangement. In the temperate climates everything is of a more subdued variety: the flowers are less bright of hue; the prevailing tint of the winged tribes is a russet brown; and the dresses of the inhabitants of these regions are of a sombre character. In the colder portions of the earth there is but little colour; the flowers are generally white or yellow, and the animals exhibit no other contrast than that which white and black afford. A chromatic scale might be formed, its maximum point being at the equator, and its minimum at the poles.[94]