The distinction, however, is not absolute: for the simple sensation is itself interesting, and the complication, if it is appreciable by sense and does not require discursive thought to grasp it, is itself beautiful. There may be a work of art in which the sensuous materials are not pleasing, as a discourse without euphony, if the structure and expression give delight; and there may be an interesting object without perceived structure, like musical notes, or the blue sky. Perfection would, of course, lie in the union of elements all intrinsically beautiful, in forms also intrinsically so; but where this is impossible, different natures prefer to sacrifice one or the other advantage. _Colour._ Sec. 17. In the eye we have an organ so differentiated that it is sensitive to a much more subtle influence than even that of air waves. There seems to be, in the interstellar spaces, some pervasive fluid, for the light of the remotest star is rapidly conveyed to us, and we can hardly understand how this radiation of light, which takes place beyond our atmosphere, could be realized without some medium. This hypothetical medium we call the ether. It is capable of very rapid vibrations, which are propagated in all directions, like the waves of sound, only much more quickly. Many common observations, such as the apparent interval between lightning and thunder, make us aware of the quicker motion of light. Now, since nature was filled with this responsive fluid, which propagated to all distances vibrations originating at any point, and moreover as these vibrations, when intercepted by a solid body, were reflected wholly or in part, it obviously became very advantageous to every animal to develope an organ sensitive to these vibrations -- sensitive, that is, to light. For this would give the mind instantaneous impressions dependent upon the presence and nature of distant objects. To this circumstance we must attribute the primacy of sight in our perception, a primacy that makes light the natural symbol of knowledge. When the time came for our intelligence to take the great metaphysical leap, and conceive its content as permanent and independent, or, in other words, to imagine _things,_ the idea of these _things_ had to be constructed out of the materials already present to the mind. But the fittest material for such construction was that furnished by the eye, since it is the eye that brings us into widest relations with our actual environment, and gives us the quickest warning of approaching impressions. Sight has a prophetic function. We are less interested in it for itself than for the suggestion it brings of what may follow after. Sight is a method of presenting psychically what is practically absent; and as the essence of the _thing_ is its existence in our absence, the _thing_ is spontaneously conceived in terms of sight.