Diderot remained three years at Vincennes. He quitted his prison in 1734, and now conceived the plan of the “Encyclopædia,” a magnificent literary and scientific monument, which alone would justify the reputation he enjoys. It occupied him, without absorbing the whole of his time, for more than thirty years; and there was certainly no other man who could have brought to the work such wide knowledge, such energy of style, and such prodigious application. He had undertaken the articles on historical, philosophical, and scientific subjects, while he was, at the same time, in association with D’Alembert, to go over the work of all the contributors. As regards many of the subjects Diderot had to study them as he went on; which his marvellous intuition enabled him to do with the best effect. “Diderot,” said Grimm, “has naturally the most encyclopædic head that ever existed.” “His genius, in its sphere of activity, includes everything,” said Voltaire. “He passes from the heights of metaphysics to the frame of a weaver, and thence to the drama.” “Centuries after the time of his existence,” wrote Rousseau, in his “Confessions,” when he had quarrelled with him, “this universal head will be looked upon as we now look upon the head of Plato or Aristotle.” Apart from his legitimate work Diderot had to cope with opposition and persecution of all kinds. The Jesuits had proposed their co-operation for the theological articles of the “Encyclopædia,” and Diderot had refused their offer equally with a similar one made by the Jansenists. The work was forthwith denounced as irreligious; and with such contributors as Diderot and Voltaire it could scarcely, indeed, have been otherwise, though it was not the direct object of the writers to make war upon Faith. Among the many celebrated authors who furnished articles to the “Encyclopædia” Rousseau may in particular be mentioned. But like most of the contributors he wrote only for a time, and chiefly on musical subjects. D’Alembert, Voltaire, Rousseau, all fell off; Rousseau because something had offended him, Voltaire to write his own philosophical dictionary, D’Alembert because he had grown tired of the work. “I am worn out with the vexations of all kinds brought upon us by this work,” wrote D’Alembert to Voltaire in 1758. At one time its publication was forbidden, when Catherine II. offered to continue it in Russia. The volumes were, curiously enough, thrown into the Bastille; which, since they could be taken out again, was at least better than burning them at the hands of the common hangman.