and the most powerful inspiration, and there is need in the art of sculpture for the rarest qualities of the greatest minds.  The art of drawing is entirely different.  It is all illusion, it deals only in appearances.  Its aim is to depict on a flat surface the aspect of objects supposed to stand behind it and to be seen through it, and its means are two branches of the science of optics.  It is based on the study of perspective and on the study of the way light falls upon objects and reveals their shapes and the direction of their surfaces by the varying degrees of their illumination.  Of this art a sculptor in the round need not necessarily know anything, and, in fact, many of them, unfortunately, know altogether too little of it.  The maker of a statue need not think about foreshortenings:  if he gives the correct form the foreshortening will take care of itself.  Sometimes it does so in a disastrous manner!  Theoretically he need not worry over light and shade, although of course he does, in practice, think about it and rely upon it, more or less.  If he gives the true forms they will necessarily have the true light and shade.  But low relief, standing between sculpture and drawing, is really more closely related to drawing than to sculpture—­is really a kind of drawing—­and this is why so few sculptors succeed in it.

It is a kind of drawing but an exceedingly difficult kind—­the most delicate and difficult of any of the arts that deal with form alone.  As to the contour, it stands on the same ground with drawing in any other material.  The linear part of it requires exactly the same degree and the same kind of talent as linear design with a pen or with a burin.  But for all that stands within the contour, for the suggestion of interior forms and the illusion of solidity, it depends on means of the utmost subtlety.  It exists, as all drawing does, by light and shade, but the shadows are not produced by the mere darkening of the surface—­they are produced by projections and recessions, by the inclination of the planes away from or toward the light.  The lower the relief the more subtle and tender must be the variation of the surface which produces them, and therefore success in relief is one of the best attainable measures of a sculptor’s fineness of touch and perfection of craftsmanship.  But as the light and shade is produced by actual forms which are yet quite unlike the true forms of nature, it follows that the artist in relief can never imitate either the shape or the depth of the shadow he sees in nature.  His art becomes one of suggestions and equivalents—­an art which can give neither the literal truth of form nor the literal truth of aspect—­an art at the farthest remove from direct representation.  And success in it becomes, therefore, one of the best tests of a sculptor’s artistry—­of his ability to produce essential beauty by the treatment of his material, rather than to imitate successfully external fact.