D’Alembert declined the education of the hereditary Grand Duke, just as he had declined the presidency of the Academy at Berlin; an infidel and almost a materialist by the geometer’s rule, who knows no power but the laws of mathematics, he did not carry into anti-religious strife the bitterness of Voltaire, or the violence of Diderot. “Squelch the thing! you are always repeating to me,” he said to Voltaire on the 4th of May, 1762. “Ah! my good friend, let it go to rack and ruin of itself, it is hurrying thereto faster than you suppose.” More and more absorbed by pure science, which he never neglected save for the French Academy, whose perpetual secretary he had become, D’Alembert left to Diderot alone the care of continuing the _Encyclopaedia_. When he died, in 1783, at fifty-six years of age, the work had been finished nearly twenty years. In spite of the bad faith of publishers, who mutilated articles to render them acceptable, in spite of the condemnation of the clergy and the severities of the council, the last volumes of the _Encyclopaedia_ had appeared in 1765. This immense work, unequal and confused as it was, a medley of various and often ill-assorted elements, undertaken for and directed to the fixed end of an aggressive emancipation of thought, had not sufficed to absorb the energy and powers of Diderot. “I am awaiting with impatience the reflections of _Pantophile Diderot on Tancrede,_” wrote Voltaire: “everything is within the sphere of activity of his genius: he passes from the heights of metaphysics to the weaver’s trade, and thence he comes to the stage.” The stage, indeed, occupied largely the attention of Diderot, who sought to introduce reforms, the fruit of his own thought as well as of imitation of the Germans, which he had not perhaps sufficiently considered. For the classic tragedies, the heritage of which Voltaire received from the hands of Racine, Diderot aspired to substitute the natural drama. His two attempts in that style, _Le Pere de Famille_ and _Le Fils natural,_ had but little success in France, and contributed to develop in Germany the school already founded by Lessing. An excess of false sensibility and an inflation of expression had caused certain true ideas to fall flat on the French stage.