I am bound, in the first place, gratefully to acknowledge the kind and complimentary notice which, notwithstanding our difference of opinion, this author has been pleased to take of my works; and, in the second, to assure him that if any of them profess to be “royal roads to art,” or to “map the mighty maze of a creative mind,” they certainly profess to do more than I ever meant they should; for I never entertained the idea that a system of æsthetic culture, even when based upon a law of nature, was capable of effecting any such object. But I doubt not that this too common misapprehension of the scope and tendency of my works must arise from a want of perspicuity in my style. I have certainly, on one occasion,[27] gone the length of stating that as poetic genius must yield obedience to the rules of rhythmical measure, even in the highest flights of her inspirations; and musical genius must, in like manner, be subject to the strictly defined laws of harmony in the most delicate, as well as in the most powerfully grand of her compositions; so must genius, in the formative arts, either consciously or unconsciously have clothed her creations of ideal beauty with proportions strictly in accordance with the laws which nature has set up as inflexible standards. If, therefore, the laws of proportion, in their relation to the arts of design, constitute the harmony of geometry, as definitely as those that are applicable to poetry and music produce the harmony of acoustics; the former ought, certainly, to hold the same relative position in those arts which are addressed to the eye, that is accorded to the latter in those which are addressed to the ear. Until so much science be brought to bear upon the arts of design, the student must continue to copy from individual and imperfect objects in nature, or from the few existing remains of ancient Greek art, in total ignorance of the laws by which their proportions are produced, and, what is equally detrimental to art, the accuracy of all criticism must continue to rest upon the indefinite and variable basis of mere opinion.