It follows, that in every hue of _red_, yellow and blue are subordinate; in every hue of _yellow_, red and blue are subordinate; and in every hue of _blue_, red and yellow are subordinate. In like manner, in every hue of _green_, red is subordinate; in every hue of _orange_, blue is subordinate; and in every hue of _purple_, yellow is subordinate. By the union of two primary colours, in the production of a secondary colour, the nature of both primaries is altered; and as there are only three primary or simple colours in the scale, the two that are united harmonically in a compound colour, form the natural contrast to the remaining simple colour. Notwithstanding all the variety that extends beyond the six positive colours, it may be said that there are only three proper contrasts of colour in nature, and that all others are simply modifications of these. Pure red is the most perfect contrast to pure green; because it is characterised amongst the primary colours by warmth of tone, while amongst the secondary colours green is distinguished by coolness of tone, both being equally related to the primary elements of light and shade. Pure yellow is the most perfect contrast to pure purple; because it is characterised amongst the primary colours as most allied to light, whilst pure purple is characterised amongst the secondaries as most allied to shade, both being equally neutral as to tone. Pure blue is the most perfect contrast to pure orange; because it is characterised amongst the primary colours as not only the most allied to shade, but as being the coolest in tone, whilst pure orange is characterised amongst the secondaries as being the most allied to light and the warmest in tone. The same principle operates throughout all the modifications of these primary and secondary colours. Such is the simple nature of contrast upon which the beauty of colouring mainly depends. It being now established as a scientific fact, that the effect of light upon the eye is the result of an ethereal action, similar to the atmospheric action by which the effect of sound is produced upon the ear; also, that the various colours which light assumes are the effect of certain modifications in this ethereal action;—just as the various sounds, which constitute the scale of musical notes, are known to be the effect of certain modifications in the atmospheric action by which sounds in general are produced: