To furnish her with money, literary spendthrift that he was, he wrote books of the most varied kinds, from “Pensées Philosophiques,” one of his most admirable works, to “Les Bijoux Indiscrets,” one of the most objectionable. No one complained of the licentious tale. But the philosophical work, a pamphlet of some sixty pages, full of profound truths, expressed with vivacity and originality, was first attributed to Voltaire, and next burnt by the common hangman. In his “Letter on the Blind,” Diderot gave further offence, and this time he was imprisoned in the castle of Vincennes. Everyone thought that the materialism professed by Diderot in his essay was the cause of his arrest; which, however, was due to something quite different. His “Lettre sur les Aveugles” had been written on the occasion of an operation for cataract performed by Réaumur on a patient who had been blind from birth. Diderot had wished to study the first sensations produced upon the blind man by the effect of light; but the famous operator would admit no one except a lady of fashion, Mme. Dupré de Saint-Maur; and at the beginning of his letter Diderot complained of the man of science who had preferred to have his experiment witnessed by two beautiful eyes rather than by men capable of appreciating it. Mme. Dupré de Saint-Maur is said to have had considerable influence with M. d’Argençon, the Minister of Police; and without judgment or accusation Diderot was arrested on the 24th of July, 1749, and taken to the Château of Vincennes. Thus religion was avenged, and Mme. Dupré de Saint-Maur also. [Illustration: GRIMM AND DIDEROT.] That Diderot’s arrest was due in a great measure to the general contents of his book, and not merely to his by no means uncomplimentary mention of Mme. Dupré de Saint-Maur, seems proved by the fact that after imprisoning him the police visited Diderot’s house and made a search for his manuscripts. The unhappy author remained for twenty-eight days in secret confinement. At the end of that time he wrote to D’Argençon begging the minister to liberate him from a captivity “in which he might make him die but could not make him live.” He was now transferred from the castle-dungeon to the castle itself, where his wife and several of his friends were allowed to visit him, among others Jean Jacques Rousseau, with whom for some time past he had been on intimate terms.