Inferences from Phenomena (Propositions 1 and 2 Book 3)
This chapter reviews Newton’s definitions with emphasis on his theoretical concept of a centripetal force. It reviews his treatment of time, space, motion, Laws of Motion and their corollaries, before emphasizing the empirical support Newton cites for his Laws of Motion. The Laws of Motion, together with theorems derived from them, afford systematic dependencies that make orbital phenomena measure features of centripetal forces maintaining bodies in those orbits. This chapter gives an account of Newton’s inferences to the centripetal direction of and inverse-square variation of the forces maintaining satellites and planets in their respective orbits of Jupiter, Saturn and the sun. It also discusses a number of philosophical lessons these inferences can teach us about scientific method. Appendix 1 gives details of Newton’s appeal to pendulum experiments. Appendix 2 exhibits Newton’s proofs of propositions 1-4 of book 1. Appendix 3 extends Newton’s precession theorem to orbits of large eccentricity.
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