In the eighth book of his “Confessions” Rousseau relates how a visit he made to the prisoner of Vincennes marked an epoch in his life. The Academy of Dijon had just proposed the following subject for a prize essay:--“Has the revival of Arts and Letters contributed to the purification of manners?” It was during his visits to Diderot in the Château that Rousseau claims not only to have conceived the idea of treating the question proposed, but also to have written the greatest part of the essay which was to cause such a sensation in the world. Diderot, however, gave a very different account of the matter to his friend Marmontel. “I was prisoner at Vincennes,” he said, “where Rousseau came to see me. He had made me his Aristarchus, as he himself declared. One day, when we were walking together, he told me that the Academy of Dijon had just proposed an interesting question, and that he wished to treat it. The question was ‘Has the revival of arts and letters contributed to the perfection of morals?’ ‘Which side shall you take?’ I said to him. ‘The affirmative,’ he replied. ‘That is the _pons asinorum_,’ I said. ‘All the mediocre people will take that view, and you can only support it by commonplace ideas; whereas the contrary side offers to philosophy and eloquence a new and fertile field.’ ‘You are right,’ he answered, after a moment’s reflection. ‘I will follow your advice.’” Diderot himself wrote on this very subject: “When the programme of the Academy of Dijon appeared he came to consult me as to which side he should take. ‘Take the side,’ I said to him, ‘that no one else will take.’” It was, in any case, Rousseau who wrote the essay, author though Diderot may have been of its paradoxical character. As an example of the laxity, as well as the severity of the period, it may be mentioned that when Diderot had once been set free from the dungeon, he was allowed, in his more commodious place of residence, to receive not only his wife and friends, but also Mme. de Pinsieux, to whom he was still attached. One day, when she was visiting him, he was struck by the brilliancy of her attire. She accounted for the elaborateness of her toilette by saying that she was going to an entertainment at Champigny. “Was she going alone?” he asked. “Quite alone.” “Your word of honour?” “I give it you.” Diderot did not quite believe in the lady’s assurances, and soon after her departure he climbed over the wall of the park, hurried to Champigny, and there saw Mme. de Pinsieux with some admirer. He went back, scaled the wall a second time, and became once more a captive, but with a heart set free. “He broke for ever,” says an indignant moralist, “with his unworthy mistress.” [Illustration: STATUE OF DIDEROT, BOULEVARD ST.-GERMAIN, FACING THE RUE ST.-BENOIT.]