Mirabeau was not the only polemic of genius who helped to sharpen against the gratings of Vincennes the weapons of the dawning Revolution. Was not Diderot of the _Encyclopedia_ there also? He paid by a month's rigorous imprisonment in the dungeon, and a longer period of mild captivity in the château, the publication of his _Letter on the Blind for the Use of those who See_. This, at least, was the ostensible reason of his detention; the true reason was never quite apparent. At the château he was allowed the visits of his wife and friends, and amongst the latter Jean Jacques Rousseau was frequently admitted. Literary legend is more responsible than history for the statement that the first idea of the _Social Contract_ was the outcome of Rousseau's talks with Diderot and Grimm in the park of Vincennes. ------- Year after year, reign after reign, the picture rarely changes within the four walls of the dungeon. Vincennes was perhaps fuller under Louis XV. than in the reigns of preceding or succeeding sovereigns, but the difference could not have been great. During the twenty years of Cardinal Fleury's ministry under Louis XV., 40,000 _lettres de cachet_ were issued by him, mostly against the Jansenists. Madame de Pompadour made a lavish use of the _lettres_ in favour of Vincennes; Madame Dubarry bestowed her patronage chiefly on the Bastille. Richelieu at one epoch, Mazarin at another, found occupants in plenty for the cells of Vincennes. It was Richelieu who passed a dry word one day apropos of certain mysterious deaths in the dungeon. "It must be grief," said one. "Or the purple fever," said the King. "It is the air of Vincennes," observed Richelieu, "that marvellous air which seems fatal to all who do not love his Majesty." ------- Ministers themselves were apt to fall by the weapon of their own employment. A minister of Louis XIV., who had chosen for his proud device the motto, _Quò non ascendam?_—_What place too high for me?_—and whom chroniclers have suspected of pretensions to the gallant crown of Mademoiselle de la Vallière, fell one day from a too giddy pinnacle plump into the dungeon of Vincennes. It was Fouquet the magnificent.