  Descartes presented his results in major works published during his lifetime: the Discourse on the Method (in French, 1637), with its essays, the Dioptrics, Meteorology, and Geometry; the Meditations on First Philosophy (i.e., on metaphysics), with its Objections and Replies (in Latin, 1641, 2nd edn. 1642); the Principles of Philosophy, covering his metaphysics and much of his natural philosophy (in Latin, 1644); and the Passions of the Soul, on the emotions (in French, 1649). Important works published posthumously included his Letters (in Latin and French, 1657–67); World, or Treatise on Light, containing the core of his natural philosophy (in French, 1664); Treatise on Man (in French, 1664), containing his physiology and mechanistic psychology; and the Rules for the Direction of the Mind (in Latin, 1701), an early, unfinished work attempting to set out his method.