XV. His Letters may be regarded as Treatises; the collection we have of them is a treasure not only of public but of literary history, and contains many dissertations on the most important subjects. The XXXIst, to Gerard Vossius, and XXXIIId, to John Utengobard, treat of Predestination and Grace, according to the Arminian system. We have already spoken of the LIVth, addressed to Du Maurier, the French Ambassador in Holland, and containing a method of study for grown persons. The LXIId, to the Baron de Langerac, the Dutch Ambassador in France, is a formal treatise on a piece of Du Moulin concerning the government of the ancient Church; the means of reconciling Grace with Free-will; and the authority of Sovereigns in matters ecclesiastical. He treats in the XCIst, to Vossius, of the effects of Christ's death. The CCLXIVth, to the celebrated Nicholas Peyresc, Counsellor of the Parliament of Aix, is rather a book than a letter, being a collection of all that the Ancients have said of Nicholas Damascenus, which leaves us at a loss with regard to nothing that could be known concerning that celebrated writer. The CCCXXIXth, to John Descordes, Canon of Limoges, treats of the power of Bishops over the Monks, and several other points of the ancient Church discipline. He proves, in the CCCLVIIth, to Jerom Bignon, Advocate-General, that the letter ascribed to Pope Clement, which was published in 1633, is really his. His letters to his brother treat of the Law of Nature and several points of Civil Law: and a letter, addressed to John Isaac Pontanus, contains his remarks on what Cluverius has said of the antiquities of Germany. The most interesting literary occurrences of his time are to be found in his letters, always accompanied, with instructing reflections: in fine, his negotiations, and the great events of the last ten years of the reign of Lewis XIII, are very particularly, and, for the most part, very truly related in them.