Diderot inaugurated modern art criticism by the notices of the pictures in the Salon, which he wrote during many years for “Grimm’s Correspondence.” One cannot help regretting that he was not born among a greater group of artists. Chardin we still esteem, and Greuze is at the height of his popularity, but it is difficult to take more than an antiquarian interest in Boucher, and who cares now for Loutherbourg or Van Loo? Even before Joseph Vernet, whose variety, freshness, and love of nature appealed so strongly to Diderot, it sometimes requires an effort to be sympathetic. Diderot now and then criticizes with severity--as occasionally when he is dealing with Boucher--but the tone of his criticism, as generally happens with contemporary criticism, seems to us to-day pitched altogether too high. In one respect, at all events, it is unlike most old appreciations of now neglected pictures; it is generally delightful to read, perhaps sometimes more delightful than the picture can ever have seemed. One suspects that Diderot treated pictures like books; Holbach, having read a book he had warmly recommended, came to him to say that the book contained nothing of which he had spoken. “Well,” replied Diderot, “if it wasn’t there it ought to have been there.” Everything that Diderot touched he vitalized. There were few things that he left untouched. There were very few roads of modern life on which he was not an enthusiastic and often audacious pioneer. He seems to have known instinctively the things that we are laboriously learning. So it is with politics, sexual morality, various social and politico-economical questions, education, philosophy. He touched all the social questions which absorb our attention to-day. He approached the problem of the place of the workers in society in the same temper in which we approach it to-day, and the practical knowledge of industries and industrial life which he had obtained in order to write some of his most remarkable articles in the “Encyclopædia” gave him some right to be heard.