Therefore, as harmony may thus be impressed upon the mind through either of these two art senses—hearing and seeing—the principles which govern the modifications in the ethereal action of light, so as to produce through the eye the effect of harmony, cannot be supposed to differ from those principles which we know govern the modifications of the atmospheric action of sound, in producing through the ear a like effect. I shall therefore endeavour to illustrate the science of beauty as evolved in colours, by forming scales of their various modifications agreeably to the same Pythagorean system of numerical ratio from which the harmonic elements of beauty in sounds were originally evolved, and by which I have endeavoured in this, as in previous works, to systematise the harmonic beauty of forms. [Illustration] It will be observed, that with a view to avoid complexity as much as possible, I have, in the arrangement of the above series of scales, not only confined myself to the merely elementary parts of the Pythagorean system, but have left out the harmonic modifications upon (¹⁄₁₁) and (¹⁄₁₃), in order that the arithmetical progression might not be interrupted.[23] The above elementary process will, I trust, be found sufficient to explain the progress, by harmonic union, of a primary colour to a toned gray, and how the simple and compound colours naturally arrange themselves into the elements of five scales, the parts of which continue from primary to secondary colour; from secondary colour to primary hue; from primary hue to secondary hue; from secondary hue to primary-toned gray; and from primary-toned gray to secondary-toned gray in the simple ratio of 2:1; thereby producing a series of the most beautiful and perfect contrasts. The natural arrangement of the primary colours upon the solar spectrum is red, yellow, blue, and I have therefore adopted the same arrangement on the present occasion. Red being, consequently, the first tonic, and blue the second, the divisions express the numerical ratios which the colours bear to one another, in respect to that colourific power for which red is pre-eminent. Thus, yellow is to red, as 2:3; blue to yellow, as 3:4; purple to orange, as 5:6; and green to purple, as 6:7. The following series of completed scales are arranged upon the foregoing principle, with the natural connecting links of red-orange, yellow-orange, yellow-green, and blue-green, introduced in their proper places. The appropriate terminology of musical notes has been adopted, and the scales are composed as follows:— Scale I. consists of primary and secondary colours; Scale II. of secondary colours and primary hues; Scale III. of primary and secondary hues; Scale IV. of secondary hues and primary-toned grays; and Scale V. of primary and secondary-toned grays;