Descartes doesn't begin his account of light until the last several chapters of the treatise. In this group of chapters, he begins to lay the groundwork for that account in several steps:

• In chs. 1-2, Descartes declares and justifies his commitment to a mechanical account of light and other phenomena. You will notice similarities to the selection from Galileo's The Assayer that you read earlier.
• Descartes begins the description of his mechanical account in chs. 3-5 by setting out what he takes to be the material constituents of the universe. Descartes is mainly interested in presenting similarities and differences between his view and Aristotelian physics, which was the natural comparison for people at the time. But what he says also distinguishes the sort of corpuscular view of matter he proposed from the atoms-in-the-void picture of ancient atomism, which was revived by people like Gassendi and came to fit easily with Newton's physics.
• In ch. 6, Descartes shifts gears and presents as a fable his "description of a new world" arising out of chaos. Later he said of his approach in The World, "For the very purpose of putting all these topics somewhat in shadow, and being able to express myself freely about them, without being obliged to adopt or to refute the opinions which are accepted by the learned, I resolved to leave all this world to their disputes, and to speak only of what would happen in a new world ..." (Discourse on Method, V, Haldane and Ross, tr.). Even though Descartes' may have been responding to literary considerations or his specific intellectual context, his reference to "fable" is an early example of comparisons of role of scientific hypotheses to fiction, and such comparisons have influenced thinking about modern science in a number of important ways in the centuries since Descartes.
• Ch. 7 is Descartes' account of the laws of nature of his new world. This includes some of his key contributions to the development of early modern physics. He refers near the end to rules governing the behavior of bodies in collision. The handout gives his statement of such rules in his later work, Principles of Philosophy. They are of mixed value and their weakness led others to develop the concept of kinetic energy, an important addition to the means Descartes provided for thinking about motion.

As you read The World, you should practice thinking about the world as a Cartesian physicist might have. These chapters provide the basic materials for this account, so approach them not only as an example of early modern thinking about science but also as a path into a particular way of thinking about the world. That is, try to respond to the book in part as you might a popular presentation of scientific view of the world. And remind yourself of Descartes' presentation of his world as a fiction if you find it difficult to set aside your awareness that he is often wrong about the world you know.