The final principle of natural beauty to which the author would call attention is the law of _Radiation_, which is in a manner a return to the first, the law of _Unity_. The various parts of any organism radiate from, or otherwise refer back to common centers, or foci, and these to centers of their own. The law is represented in its simplicity in the star-fish, in its complexity in the body of man; a tree springs from a seed, the solar system centers in the sun. The idea here expressed by the term "radiation" is a familiar one to all students of theosophy. The Logos radiates his life and light throughout his universe, bringing into activity a host of entities which become themselves radial centers; these generate still others, and so on endlessly. This principle, like every other, patiently publishes itself to us, unheeding, everywhere in nature, and in all great art as well; it is a law of optics, for example, that all straight lines having a common direction if sufficiently prolonged appear to meet in a point, i.e., radiate from it (Illustration 31). Leonardo da Vinci employed this principle of perspective in his Last Supper to draw the spectator's eye to the picture's central figure, the point of sight toward which the lines of the walls and ceiling converge centering in the head of Christ. Puvis de Chavannes, in his Boston Library decoration, leads the eye by a system of triangulation to the small figure of the Genius of Enlightenment above the central door (Illustration 32); and Ruskin, in his _Elements of Drawing_, has shown how artfully Turner arranged some of his compositions to attract attention to a focal point. This law of Radiation enters largely into architecture. The Colosseum, based upon the ellipse, a figure generated from two points or foci, and the Pantheon, based upon the circle, a figure generated from a central point, are familiar examples. The distinctive characteristic of Gothic construction, the concentration or focalization of the weight of the vaults and arches at certain points, is another illustration of the same principle applied to architecture, beautifully exemplified in the semicircular apse of a cathedral, where the lines of the plan converge to a common center, and the ribs of the vaulting meet upon the capitals of the piers and columns, seeming to radiate thence to still other centers in the loftier vaults which finally meet in a center common to all. [Illustration 30] [Illustration 31] [Illustration 32]