The ‘Philosophical Thoughts’ had made men turn and look at him. True, their audacious freedom was not pleasing to the government; but what did a Diderot care for that? His ideas rolled off his pen as the words rolled off his tongue. ‘I do not compose, I am no author,’ he wrote once. ‘I read, or I converse. I ask questions, or I give answers.’ The lines should be placed as a motto over each of his works. That they are literally true accounts for all his defects as a writer, and for all his charm. In 1749 he happened to be talking about a certain famous operation for cataract, and afterwards wrote down his reflections on it. To a man born blind, atheism, said Diderot, is surely a natural religion. He sent his ‘Letter on the Blind for the Use of Those Who See’ to the great chief of the party of which his ‘Philosophical Thoughts’ had proclaimed himself a member. Voltaire replied that, for his part, if he were blind, he should have recognised a great Intelligence who provided so many substitutes for sight; and the friendship between Arouet and Denis was started with a will. On July 24, 1749, Diderot found himself a prisoner in the fortress of Vincennes. He was not wholly surprised. No literary man was astonished at being imprisoned in those days. Diderot was perfectly aware that since the publication of the ‘Philosophical Thoughts’ he had been suspect of the police; he was also aware that his ‘Letter on the Blind’ contained a sneer on the subject of a fine lady, the _chère amie_ of d’Argenson, the War Minister. For company he had ‘Paradise Lost’ and his own buoyant temperament. He made a pen out of a toothpick, and ink out of the slate scraped from the side of his window, mixed with wine; and with characteristic good-nature wrote down this simple recipe for writing materials on the wall of his cell for the benefit of future sufferers. Better than all, he was the friend of Voltaire, and Voltaire’s Madame du Châtelet was a near relative of the governor of Vincennes. After twenty-one days of wire-pulling, Socrates Diderot, as Madame du Châtelet called him, was removed, as the fruit of her efforts, from the fortress to the castle of Vincennes, put on parole, allowed the society of his wife and children, with pen, ink, and books to his heart’s content. One day Madame Puisieux came to see him--in attire too magnificent to be entirely for the benefit of a poor dog of a prisoner like myself, thinks Denis. That night he climbed over the high wall of the _enceinte_ of the castle, and finding her, as he had expected, amusing herself with another admirer at a _fête_, renounced her as easily and hotly as he had fallen in love with her. He had one far more famous visitor in Vincennes, Jean Jacques Rousseau. As they walked together in the wood of Vincennes, Denis, with his overrunning fecundity of idea, suggested to Jean Jacques, it is said, the matter for that essay, sometimes called the ‘Essay against Civilisation,’ which first made him famous.