Then living in Paris, some six-and-thirty years old, the author of the ‘Philosophical Thoughts,’ and the most fascinating scoundrel in France, was Denis Diderot. With the quiet d’Alembert, of morals almost austere and of hidden, frugal life, what could a Diderot have in common? Something more than the attraction of opposites drew them together. The vehement and all-embracing imagination of the one fired the calm reason of the other. The hot head and the cool one were laid together, and the result was the great Encyclopædia. The first idea of the pair was modest enough--to translate into French the English Encyclopædia of Chambers. But had not brother Voltaire said that no man who could make an adequate translation ever wasted his time in translating? They soon out-ran so timid an ambition. The thing must not only be spontaneous work; it must wholly surpass all its patterns and prototypes. It must be not _an_ Encyclopædia, but _the_ Encyclopædia. Every man of talent in France must bring a stone towards the building of the great Temple. From Switzerland, old Voltaire shall pour forth inspiration, encouragement, incentive. Rousseau shall lend it the glow of his passion, and Grimm his journalistic versatility. Helvétius shall contribute--d’Holbach, Turgot, Morellet, Marmontel, Raynal, La Harpe, de Jaucourt, Duclos. And the Preliminary Discourse shall be the work of d’Alembert. An envious enemy once dismissed him scornfully as ---- Chancelier de Parnasse, Qui se croit un grand homme et fit une préface. Yet if he had written nothing but that Preface he would still have had noble titles to fame. It contained, as he himself said, the quintessence of twenty years’ study. If his style was usually cold and formal, it was not so now. With warmest eloquence and boldest brush he painted the picture of the progress of the human mind since the invention of printing. From the lofty heights man’s intellect had scaled there stood out yet mightier heights for him to dare! Advance! advance! If ever preface said anything, the Preface to the great Encyclopædia says this. Clothed with light and fire, that dearest son of d’Alembert’s genius went forth to illuminate and to astound the world. At first the Encyclopædia was not only heard gladly by the common people, but was splendidly set forth with the approbation and _Privilège du Roi_. Even the wise and thoughtful melancholy of d’Alembert’s temperament may have been cheered by such good fortune, while the sanguine Diderot naturally felt convinced it would last for ever.