Peculiarly interesting is the application of this mode of study to the art of music. The expression of feeling through sounds combined in beautiful forms, gives us an opportunity, as cannot be too often pointed out,[1] for a much freer and more self-determined activity than we can enjoy in our other artistic pursuits. Because the art of music, both in its material and in its content, is less shackled, less thwarted in its characteristic processes, than the representative arts, its evolution is remarkably obvious and easy to trace. Its material, in the first place, is a product of man’s free selection; that complex system of musical tones which he has constructed by many centuries of work, is his own, to use as he will, in a sense in which language, natural objects, and physical substances can never be. Whereas the growth of poetry, of painting, of sculpture, of architecture, is complicated and distorted by a thousand external conditions, that of music is determined by its own inner laws alone,--by the laws, that is to say, of sound-production, of sound-perception, and of psychology. In the second place, the content of music, that which it expresses by means of these freely selected and composed tones, is purely internal. It is easy to see that the objects of musical expression, namely, human emotions in their essence, reduced, so to speak, to their lowest terms, are more fluid to manipulation than the comparatively fixed, indocile, and external objects of the representative arts. By virtue, then, both of its material medium and of its ideal content, music enjoys, among human modes of expression, a unique freedom and autonomy. It grows, not under pressure from outside, but by its own inner vitality; its forms are determined, not by correspondence with anything in the heavens or on the earth, but, like those of the snow-crystals, by the inexorable laws that govern it; and the particular changes it undergoes in its evolution, marking merely successive incarnations of tendencies and potencies always implicit in it, can be traced with comparative ease, clearness, and certainty.