  When The World had become ready for publication in 1633, upon hearing of the Church’s condemnation of Galileo (1564–1642) in the same year, Descartes decided against its publication. For, the world system he had adopted in the book assumed, as did Galileo’s, the heliocentric Copernican model. In a letter to Mersenne, dated November 1633, Descartes expresses his fear that were he to publish The World, the same fate that befell Galileo would befall him. And, although this is something that he understandably would want to avoid, some scholars question Descartes’ expressed concern, for his living in the Netherlands would have kept him out of reach of Catholic authorities. The World appears to have been constituted of several smaller, but related, works: a treatise on physics, a treatise on mechanics (machines), a treatise on animals, and a treatise on man. Although much of The World has been lost, some of it seems to have survived in the form of essays attached to the Discourse which, as was mentioned earlier, would be published four years later, in 1637. And, some of it was published posthumously. Arguably, Constantijn Huygens (1596–1687) received what Descartes refers to as “three sheets” of The World, along with a letter dated 5 October 1637. These “sheets” deal primarily with mechanics.