This book is a historical-epistemological study of one of the most consequential breakthroughs in the history of celestial mechanics: Robert Hooke's (1635-1703) proposal to "e;compoun[d] the celestial motions of the planets of a direct motion by the tangent & an attractive motion towards a centrat body"e; (Newton, The Correspondence li, 297. Henceforth: Correspondence). This is the challenge Hooke presented to Isaac Newton (1642-1727) in a short but intense correspondence in the winter of 1679-80, which set Newton on course for his 1687 Principia, transforming the very concept of "e;the planetary heavens"e; in the process (Herivel, 301: De Motu, Version III). 1 It is difficult to overstate the novelty of Hooke 's Programme * The celestial motions, it suggested, those proverbial symbols of stability and immutability, werein fact a process of continuous change: a deflection of the planets from original rectilinear paths by "e;a centraU attractive power"e; (Correspondence, li, 313). There was nothing necessary or essential in the shape of planetary orbits. Already known to be "e;not circular nor concentricall"e; (ibid. ), Hooke claimed that these apparently closed "e;curve Line[ s ]"e; should be understood and calculated as mere effects of rectilinear motions and rectilinear attraction. And as Newton was quick to realize, this also implied that "e;the planets neither move exactly in ellipse nor revolve twice in the same orbit, so that there are as many orbits to a planet as it has revolutions"e; (Herivel, 301: De Motu, Version III).

This book is a historical-epistemological study of one of the most consequential breakthroughs in the history of celestial mechanics: Robert Hooke's (1635-1703) proposal to "e;compoun[d] the celestial motions of the planets of a direct motion by the tangent & an attractive motion towards a centrat body"e; (Newton, The Correspondence li, 297. Henceforth: Correspondence). This is the challenge Hooke presented to Isaac Newton (1642-1727) in a short but intense correspondence in the winter of 1679-80, which set Newton on course for his 1687 Principia, transforming the very concept of "e;the planetary heavens"e; in the process (Herivel, 301: De Motu, Version III). 1 It is difficult to overstate the novelty of Hooke 's Programme * The celestial motions, it suggested, those proverbial symbols of stability and immutability, werein fact a process of continuous change: a deflection of the planets from original rectilinear paths by "e;a centraU attractive power"e; (Correspondence, li, 313). There was nothing necessary or essential in the shape of planetary orbits. Already known to be "e;not circular nor concentricall"e; (ibid. ), Hooke claimed that these apparently closed "e;curve Line[ s ]"e; should be understood and calculated as mere effects of rectilinear motions and rectilinear attraction. And as Newton was quick to realize, this also implied that "e;the planets neither move exactly in ellipse nor revolve twice in the same orbit, so that there are as many orbits to a planet as it has revolutions"e; (Herivel, 301: De Motu, Version III).