Light may be considered as an active, and darkness a passive principle in the economy of Nature, and colour an intermediate phenomenon arising from their joint influence; and it is in the ratios in which these primary principles act upon each other, by which I here intend to explain the science of beauty as evolved in colour. It has been usual to consider colour as an inherent quality in light, and to suppose that coloured bodies absorb certain classes of its rays, and reflect or transmit the remainder; but it appears to me that colour is more probably the result of certain modes in which the opposite principles of motion and rest, or force and resistance, operate in the production, refraction, and reflection of light, and that each colour is mutually related, although in different degrees, to these active and passive principles. White and black are the representatives of light and darkness, or activity and rest, and are therefore calculated as pigments to reduce colours and hues to tints and shades. Having, however, fully illustrated the nature of tints and shades in a former work,[22] I shall here confine myself to colours in their full intensity—shewing the various modifications which their union with each other produce, along with the harmonic relations which these modifications bear to the primaries, and to each other in respect to warmth and coolness of tone, as well as to light and shade. The primary colours are red, yellow, and blue. Of these, yellow is most allied to light, and blue to shade, while red is neutral in these respects, being equally allied to both. In respect to tone, that of red is warm, and that of blue cool, while the tone of yellow is neutral. The ratios of their relations to each other in these respects will appear in the harmonic scales to which, for the first time, I am about to subject colours, and to systematise their various simple and compound relations, which are as follow:— From the binary union of the primary colours, the secondary colours arise— Orange colour, from the union of yellow and red. Green, from the union of yellow and blue. Purple, from the union of red and blue. From the binary union of the secondary colours, the primary hues arise— Yellow-hue, from the union of orange and green. Red-hue, from the union of orange and purple. Blue-hue, from the union of purple and green. From the binary union of the primary hues, the secondary hues arise— Orange-hue, from the union of yellow-hue and red-hue. Green-hue, from the union of yellow-hue and blue-hue. Purple-hue, from the union of red-hue and blue-hue. Each hue owes its characteristic distinction to the proportionate predominance or subordination of one or other of the three primary colours in its composition.