Sculpture depends, as does architecture, upon certain laws of proportion in space which are analogous to the laws of proportion in time and in pitch upon which music is founded.  But as sculpture represents the human figure, whereas architecture and music represent nothing, sculpture requires for its perfection the mastery of an additional science, which is the knowledge of the structure and movement of the human body.  This knowledge may be acquired with some rapidity, especially in times and countries where man is often seen unclothed.  So, in the history of civilizations, sculpture developed early, after poetry, but with architecture, and before painting and polyphonic music.  It reached the greatest perfection of which it is capable in the age of Pericles, and from that time progress was impossible to it, and for a thousand years its movement was one of decline.  After the dark ages sculpture was one of the first arts to revive; and again it develops rapidly—­though not so rapidly as before, conditions of custom and climate being less favorable to it—­until it reaches, in the first half of the sixteenth century, something near its former perfection.  Again it can go no further; and since then it has changed but has not progressed.  In Phidias, by which name I would signify the sculptor of the pediments of the Parthenon, we have the coincidence of a superlatively great artist with the moment of technical and scientific perfection in the art, and a similar coincidence crowns the work of Michelangelo with a peculiar glory.  But, apart from the work of these two men, a the essential value of a work of sculpture is by no means always equal to its technical and scientific completeness.  There are archaic statues that are almost as nobly beautiful as any work by Phidias and more beautiful than almost any work that has been done since his time.  There are bits of Gothic sculpture that are more valuable expressions of human feeling than anything produced by the contemporaries of Buonarroti.  Even in times of decadence a great artist has created finer things than could be accomplished by a mediocre talent of the great epochs, and the world could ill spare the Victory of Samothrace or the portrait busts of Houdon.

As sculpture is one of the simplest of the arts, painting is one of the most complicated.  The harmonies it constructs are composed of almost innumerable elements of lines and forms and colors and degrees of light and dark, and the science it professes is no less than that of the visible aspect of the whole of nature—­a science so vast that it never has been and perhaps never can be mastered in its totality.  Anything approaching a complete art of painting can exist only in an advanced stage of civilization.  An entirely complete art of painting never has existed and probably never will exist.  The history of painting, after its early stages, is a history of loss here balancing gain there, of a new means of expression acquired at the cost of an old one.