manners.  There is no violent improbability in this.  Diderot, for all the robustness and penetration of his judgment, was yet often borne by his natural impetuosity towards the region of paradox.  His own curious and bold Supplement au Voyage de Bougainville is entirely in the vein of Rousseau’s discourse on the superiority of primitive over civilised life.  “Prodigious sibyl of the eighteenth century,” cries Michelet, “the mighty magician Diderot!  He breathed out one day a breath; lo, there sprang up a man—­Rousseau."[87] It is hard to believe that such an astonishing genius for literature as Rousseau’s could have lain concealed, after he had once inhaled the vivifying air of Paris.  Yet the fire and inspiring energy of Diderot may well have been the quickening accident that brought his genius into productive life.  All the testimony goes to show that it was so.  Whether, however, Diderot is really responsible for the perverse direction of Rousseau’s argument is a question of fact, and the evidence is not decisive.[88] It would be an odd example of that giant’s nonchalance which is always so amazing in Diderot, if he really instigated the most eloquent and passionate writer then alive to denounce art and science as the scourge of mankind, at the very moment when he was himself straining his whole effort to spread the arts and sciences, and to cover them with glory in men’s eyes.

Among Diderot’s other visitors was Madame de Puisieux.  One day she came clad in gay apparel, bound for a merry-making at a neighbouring village.  Diderot, conceiving jealous doubts of her fidelity, received assurance that she would be solitary and companionless at the feast, thinking mournfully of her persecuted philosopher lying in prison.  She forgot that one of the parents of philosophy is curiosity, and that Diderot had trained himself in the school of the sceptics.  That evening he scaled the walls of the park of Vincennes, flew to the scene of the festival, and there found what he had expected.  In vain for her had he written upon virtue and merit, and the unhallowed friendship came to an end.

After three months of captivity, Diderot was released.  The booksellers who were interested in the Encyclopaedia were importunate with the authorities to restore its head and chief to an enterprise that stirred universal curiosity.[89] For the first volume of that famous work was now almost ready to appear, and expectation was keen.  The idea of the book had occurred to Diderot in 1745, and from 1745 to 1765 it was the absorbing occupation of his life.  Of the value and significance of the conception underlying this immense operation, I shall speak in the next chapter.  There also I shall describe its history.  The circumstances under which these five-and-thirty volumes were given to the world mark Diderot for one of the few true heroes of literature.  They called into play some of the most admirable of human qualities.  They required a laboriousness as steady and as prolonged, a wariness as alert, a grasp of plan as firm, a fortitude as patient, unvarying, and unshaken, as men are accustomed to applaud in the engineer who constructs some vast and difficult work, or the commander who directs a hardy and dangerous expedition.