The white man in his architecture uses either the horizontal or the vertical line, or both; he takes the triangular building of the negro and places it on the square tent of the yellow man, making his house as perfect as possible; he goes further, and, in accordance with his powerfully-arched brow, over-arches not only rivers and chasms, but builds his magnificent cupolas and pointed arches, the acme of architectural forms. Ethnology then serves us as a foundation for the study of art in its different phases. Conforming to the general tendency of modern science, we have tried to express the cause of the artistic development of the three groups of humanity by figures; we have measured the seat and instrument of our intellectual faculty, and have thus tried to leave the sphere of mere conjecture, or unfounded opinion, in order to place the phenomena of art-history on a firm basis. Though art, undoubtedly, belongs ‘to the magic circle of the imagination, and the inner powers of the mind,’ those powers are dependent on our very bodily construction, the amount of brain and the facial angle. We do not deal in mere hypothesis, but submit to our readers a complete theory borne out by facts. In considering the frontispiece of our manual, representing the ‘TREE OF ART,’ we can visibly trace the slow and gradual development of the white man. The negro fixes our attention only as savage; the yellow man has a line of his own, and has remained stationary in his artistic development; the white man has passed through the savage stages, and by his own exertions, undergoing various phases of rise and decline (the real signs of historical vitality), has steadily progressed till he began to attempt, and to succeed in bringing about, ‘a harmonious connection between the representation of nature and the expression of awakened emotion, and a mysterious analogy between the emotions of his mind and the phenomena perceived by his senses.’ As all phenomena must take place in _space_ and _time_ (the two fundamental forms of all existence), the products of art must also have been executed under these two conditions, and can therefore be treated _historically_.