The two decades of retirement in the Netherlands were Descartes's productive period. His motive in developing and writing out his thoughts was, essentially, the desire not to disappoint the widely spread belief that he was in possession of a philosophy more certain than the common one. The work entitled _Le Monde_, begun in 1630 and almost completed, remained unprinted, as the condemnation of Galileo (1632) frightened our philosopher from publication; fragments of it only, and a brief summary, appeared after the author's death. The chief works, the _Discourse on Method_, the _Meditations on the First Philosophy_, and the _Principles of Philosophy_ appeared between 1637 and 1644,--the _Discours de la Méthode_ in 1637, together with three dissertations (the "Dioptrics," the "Meteors," and the "Geometry"), under the common title, _Essais Philosophiques_. To the (six) _Meditationes de Prima Philosophia_, published in 1641, and dedicated to the Paris Sorbonne, are appended the objections of various savants to whom the work had been communicated in manuscript, together with Descartes's rejoinders. He himself considered the criticisms of Arnauld, printed fourth in order, as the most important. The Third Objections are from Hobbes, the Fifth from Gassendi, the First, which were also the first received, from the theologian Caterus of Antwerp, while the Second and Sixth, collected by Mersenne, are from various theologians and mathematicians. In the second edition there were added, further, the Seventh Objections, by the Jesuit Bourdin, and the Replies of the author thereto. The four books of the _Principia Philosophiae_, published in 1644 and dedicated to Elizabeth, Countess Palatine, give a systematic presentation of the new philosophy. The _Discourse on Method_ appeared, 1644, in a Latin translation, the _Meditations_ and the _Principles_ in French, in 1647. The _Treatise on the Passions_ was published in 1650; the _Letters_, 1657-67, in French, 1668, in Latin. The _Opera Postuma_, 1701, beside the _Compendium of Music_ (written in 1618) and other portions of his posthumous writings, contain the "Rules for the Direction of the Mind," supposed to have been written in 1629, and the "Search for Truth by the Light of Nature." The complete works have been often published, both in Latin and in French. The eleven volume edition of Cousin appeared in 1824-26.[1]