In the introductory volume, ” Art in Theory,” an attempt was made to derive a true conception of the requirements of art from a study of certain facts and opinions concerning it acknowledged by all, or held by writers of authority. Guided by these criteria, nature was first distinguished from art, and then the lower arts from the higher. It was found that an essential characteristic of these latter is what is known as form, but in their cases a form producing always two apparently different effects, one derived from an imitation of external phenomena, and the other from a communication of thoughts and emotions. The first effect, tending to emphasize the form in itself, was said to be mainly, though by no means exclusively, characteristic of classic art, and the second effect, tending to emphasize the significance in the form, was said to be mainly characteristic of romantic art. It was also argued that the emphasizing of either of these tendencies, if carried so far as to involve a neglect of the other of them, is fatal to artistic excellence. In indicating, then, the conception of artistic aims best tending to preserve the equilibrium between the two tendencies, it was pointed out that art neither imitates nor communicates in the most practically effective ways. Because aiming to do both, its chief aim cannot be to do either the one or the other. Art represents natural phenomena, as one may say, as a means of representing thoughts and emotions. Or, to express this differently, art emphasizes representation, developing and elaborating the factors of it in nature, and the possibilities of it in the mind. But in doing this, art is using the same means and continuing the same modes of expression as those that are attributed by men to the creative and divine intelligence. The impulse to art, therefore, may be considered creative and divine. But as it neither imitates nor communicates in the most usefully effective way, we must trace it less to the useful than to the non-useful and so to what in elementary phases is called the play-impulse. This play-impulse, even in dogs and kittens, to say nothing of apes, tends to the imitation of that which seems interesting, attractive, and charming in one’s surroundings. The same impulse, when turned in the direction of art, inasmuch as this always involves the use of form, tends also to imitation. But an imitation of that which is interesting, attractive, and charming in form, especially in form communicating to mind and spirit the suggestions of a creative and divine impulse, is nothing more nor. less than a reproduction of what men, when using the term in its highest sense, mean by beauty. What is there in beauty, however, that it should be used by the art-impulse when giving expression to the mental and spiritual? A review, which follows, of the history of opinion on the subject, reveals that the effects of beauty are well-nigh universally attributednot always explicitly but certainly implicitlyin part to form, but in part also to significance suggested by the form. In other words, the charm exerted by beauty is exerted partly upon the senses, because the elements of the form harmonize with one another and with the physiological requirements of the ear or eye, and partly upon the mind, because the suggestions of these elements harmonize with psychological requirements. The consequent definition reached is, that “Beauty is a characteristic of any complex form of varied elements, producing apprehensible unity (i. e., harmony or likeness) of effects (I) upon the motive organs of sensation in the ear or eye, or (2) upon the emotive sources of imagination in the mind, or (3) upon both the one and the other.” There are the best of reasons, therefore, why a creative and divine impulse tending to imitation should reproduce beauty, the mere existence of which alone may involve that appeal to the mental and spiritual nature which is made by what we term significance. But we must not forget that in art the mind may do more than represent significance as a secondary consideration, which would be the case did it do so merely because, by way of accident, as it were, a certain significance was necessarily suggested by the form used. The mind often represents thoughts and emotions as a primary consideration,that is, it decides upon them first, and, afterwards, selects the forms through which to communicate them. We are obliged, therefore, to know something about the ways in which the mind communicates or represents thoughts or emotions through any forms whatever, irrespective of their being characterized by beauty. The remainder of the book shows how, at different stages of the influence exerted by precisely the same external phenomena, entirely different phases of conscious thoughts and emotions are aroused to activity. This activity is analyzed into that which primarily is instinctive or spontaneous, is reflective or responsive, or is a blending of both the others in what may be termed the instinctively reflective or the emotive. It is shown that for every phase of activity there is only one natural form of expression; and that it is this form and no other which, when artistically developed, i. e., developed with reference to beauty, finds appropriate embodiment in one of the five arts.