The generality of mankind are, however, capable of appreciating the harmony of colour which, like that of both sound and form, arises from the simultaneous exhibition of opposite principles having a ratio to each other. These principles are in continual operation throughout nature, and from them we often derive pleasure without being conscious of the cause. All who are not colour-blind must have felt themselves struck with the harmonic beauty of a cloudless sky, although in it there is no configuration, and at first sight apparently but one colour. Now, as we know that there can be no more impression of harmony made upon the mind by looking upon a single colour, than there could be by listening to a single continued musical note, however sweet its tone, we are apt at first to imagine that the organ of vision has, in some measure, conveyed a false impression to the mind. But it has not done so; for light, when reflected from the atmosphere, produces those cool tones of blue, gray, and purple, which seem to clothe the distant mountains; but, when transmitted through the same atmosphere, it produces those numerous warm tints, the most intense of which give the gorgeous effects which so often accompany the setting sun. We have, therefore, in the upper part of a clear sky, where the atmosphere may be said to be illuminated principally by reflection from the surface of the earth, a comparatively cool tone of blue, the result of reflection, which gradually blends into the warm tints, the result of transmission through the same atmosphere. Such a composition of harmonious colouring is to the eye what the voice of the soft breath of summer amongst the trees, the hum of insects on a sultry day, or the simple harmony of the Æolian harp, is to the ear. To such a composition of chromatic harmony must also be referred the universal concurrence of mankind in appreciating the peculiar beauty of white marble statuary. That the principal constituent of beauty in such works ought to be harmony of form, no one will deny; but this is not the only element, as appears from the fact, that a cast in plaster of Paris, of a fine white marble statue, although identical in form, is far less beautiful than the original. Now this undoubtedly must be the consequence of its having been changed from a semi-translucent substance, which, like the atmosphere, can transmit as well as reflect light, to an opaque substance, which can only reflect it. Thus the opposite principles of chromatic warmth and coolness are equally balanced in white marble—the one being the natural result of the partial transmission of light, and the other that of its reflection. As a series of coloured illustrations would be beyond the scope of this _résumé_, I may refer those who wish to prosecute the inquiry, with the assistance of such a series, to my published works upon the subject.[24] THE SCIENCE OF BEAUTY, APPLIED TO THE FORMS AND PROPORTIONS OF ANCIENT GRECIAN VASES AND ORNAMENTS.