And just because there never has been a complete art of painting, entirely rounded and perfected, it is the clearer to us that the final value of a work in that art never has depended on its approach to such completion. There is no one supreme master of painting, but a long succession of masters of different yet equal glory. If the masterpieces of architecture are everywhere because there has often been a complete art of architecture, the masterpieces of painting are everywhere for the opposite reason. And if we do not always value a master the more as his art is more nearly complete, neither do we always value him especially who has placed new scientific conquests at the disposal of art. Palma Vecchio painted by the side of Titian, but he is only a minor master; Botticelli remained of the generation before Leonardo, but he is one of the immortal great. Paolo Ucello, by his study of perspective, made a distinct advance in pictorial science, but his interest for us is purely historic; Fra Angelico made no advance whatever, but he practised consummately the current art as he found it, and his work is eternally delightful. At every stage of its development the art of painting has been a sufficient medium for the expression of a great man’s mind; and wherever and whenever a great man has practised it, the result has been a great and permanently valuable work of art. For this seems, finally, to be the law of all the arts: the one essential prerequisite to the production of a great work of art is a great man. You cannot have the art without the man, and when you have the man you have the art. His time and his surroundings will color him, his art will not be at one time or place precisely what it might be at another; but at bottom the art is the man, and at all times and in all countries is just as great as the man.