PLATE 21.--THE LITTA MADONNA, BY LIONARDO DA VINCI. (HERMITAGE) 240 This is perhaps the best example known of an illusion of relief secured by shading alone. (See Page 240.) PLATE 22.--CHRIST ON THE CROSS, BY VAN DYCK. (ANTWERP MUSEUM) 252 A superb example of relief obtained by the exclusion of accessories. Van Dyck took the idea from Rubens, who borrowed it from Titian, this artist improving on Antonella da Messina. The relief of course is not well observed in the reproduction because of its miniature form. The work is usually regarded as the finest of its kind in existence. (See Page 244.) PLATE 23.--PATRICIA, BY LYDIA EMMET. (PRIVATE POSSESSION, N. Y.) 264 A very excellent example of the plan of securing relief described in Book II, Chap. I. Here also the relief is not observed in the reproduction, but the original is of life size and provides an illusion as nearly perfect as possible. (See Page 247.) PLATE 24.--THE CREATION OF ADAM, BY MICHELANGELO. (VATICAN) 276 Instance of the use of an oval form of drapery to assist in presenting an illusion of suspension in the air. (See Page 260.) PLATE 25.--THE PLEIADS, BY M. SCHWIND. (DENNER COLLECTION.) 288 One of the finest examples of illusion of motion in the air. (See Page 269.) PLATE 26.--ST. MARGARET, BY RAPHAEL. (LOUVRE) 302 Perhaps the best example in existence of a painted human figure in action. It will be seen that every part of the body and every fold of the drapery are used to assist in the expression of movement. (See Page 250.) PLATE 27.--DIANA AND NYMPHS PURSUED BY SATYRS, BY RUBENS. (PRADO) 318 A good example of an illusion of motion created by showing a number of persons in different stages of a series of consecutive actions. (See Page 254.) PLATE 28.--AUTOMEDON WITH THE HORSES OF ACHILLES, BY H. REGNAULT. (BOSTON MUSEUM, U. S. A.) 334 The extraordinary spirit and action of these horses are above the experience of life, but they do not appear to be beyond the bounds of possibility. In any case the action is perfectly appropriate here, as the animals are presumed to be immortal. (See Page 256.) PLATE 29.--MARBLE FIGURE OF ARIADNE. (VATICAN) 348 This work, of the Hellenistic period, illustrates the possibility of largely varying the regular proportions of the human figure without injury to the art, by the skilful use of drapery. (See Page 329.) Art Principles INTRODUCTION In view of the many varied definitions of "Art" which have been put forward in recent times, and the equally diverse hypotheses advanced for the solution of æsthetic problems relating to beauty, it is necessary for one who discusses principles of art, to state what he understands by the terms "Art" and "Beauty."