[Illustration: DEGAS. DANCING GIRL FASTENING HER SHOE.] Perhaps a later age may even come to recognise that Manet made an advance upon the old masters in his delicacy and scrupulous analysis of light; in that case it will esteem the discovery of tone-values as the chief acquisition of the nineteenth century, as a conquest such as has never been made in painting since the Eycks and Masaccio, since the establishment of the theory of perspective. In a treatise commanding all respect Hugo Magnus has written of how the sense of colour increased in the various periods of the world's history; since the appearance of the Impressionists, verification may be made of yet another advance in this direction. The study of tone-values has never been carried on with such conscientious exactitude, and in regard to truth of atmosphere one is disposed to believe that our eyes to-day see and feel things which our ancestors had not yet noticed. The old masters have also touched the problem of "truth in painting." It is not merely that the character of their colours often led the Italian tempera and fresco painters to the most natural method of treating light. They even occupied themselves in a theoretical way with the question. An old Italian precept declares that the painter ought to work in a closed yard beneath an awning, but should place his model beneath the open sky. In the frescoes which he painted in Arezzo in 1480, Piero della Francesca, in particular, pursued the problem of _plein-air_ painting with a fine instinct. But love of the beautiful and luminous tints, such as the technique of oil-painting enabled artists to attain at a later date, quickly seduced them from carrying out the natural treatment of light in the gradation of colour. Under the influence of oil-painting the Italians of the great period, from Leonardo onwards, turned more and more to strong contrasts. And in spite of Albert Cuyp, even the Dutch landscape painters of the seventeenth century have seen objects rather in line and form, plastically, than pictorially in their environment of light and air. The nineteenth century was the first seriously to attack a problem which--except by Velasquez--had been merely touched upon by the old schools, but never solved. [Illustration: RENOIR. SUPPER AT BOUGIVAL. (_By permission of M. Durand-Ruel, the owner of the copyright._)] [Illustration: RENOIR. THE WOMAN WITH THE FAN. (_By permission of M. Durand-Ruel, the owner of the copyright._)]