Hobbes, Galileo, and the Physics of Simple Circular Motions

In: Hobbes Studies

Hobbes tried to develop a strict version of the mechanical philosophy, in which all physical phenomena were explained only in terms of bodies in motion, and the only forces allowed were forces of collision or impact. This ambition puts Hobbes into a select group of original thinkers, alongside Galileo, Isaac Beeckman, and Descartes. No other early modern thinkers developed a strict version of the mechanical philosophy (not even Newton who allowed forces of attraction and repulsion operating at a distance). Natural philosophies relying solely on bodies in motion require a concept of inertial motion. Beeckman and Descartes assumed rectilinear motions were rectilinear, but Galileo adopted a theory which has been referred to as circular inertia. Hobbes’s natural philosophy depended to a large extent on what he called “simple circular motions.” In this paper, I argue that Hobbes’s simple circular motions derived from Galileo’s belief in circular inertia. The paper opens with a section outlining Galileo’s concept, the following section shows how Hobbes’s physics depended upon circular motions, which are held to continue indefinitely. A third section shows the difficulty Hobbes had in maintaining a strictly mechanistic philosophy, and the conclusion offers some speculations as to why Galileo’s circular inertia was never entertained as a serious rival to rectilinear inertia, except by Hobbes.

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    Isaac NewtonOpticks… Based on the Fourth Edition London 1730 (New York: Dover1979) p. 401. For fuller discussion of occult qualities in early modern natural philosophy see John Henry “Occult Qualities and the Experimental Philosophy: Active Principles in pre-Newtonian Matter Theory” History of Science 24 (1986) pp. 335–381 and Alan Gabbey et al. “New Doctrines of Body and Its Powers Place and Space” in Garber D. and Ayers M. (eds) The Cambridge History of Seventeenth-Century Philosophy (Cambridge: Cambridge University Press 1998) pp. 553–623.

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    AristotleMechanical Problems p. 333. The influence of the Mechanical Questions on Descartes has recently been explored by Helen Hattab “From Mechanics to Mechanism: The Quaestiones Mechanicae and Descartes’ Physics” in Peter R. Anstey and John A. Schuster (eds) The Science of Nature in the Seventeenth Century: Patterns of Change in Early Modern Natural Philosophy (Dordrecht: Springer 2005) pp. 99–129.

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    Ron Naylor“Paolo Sarpi and the First Copernican Tidal Theory,” British Journal for the History of Science47 (2014) pp. 661–675.

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    KoyréGalileo Studies p. 239.

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    GalileiDialogue p. 172; see also Stillman Drake “The Concept of Inertia” in Stillman Drake Essays on Galileo and the History and Philosophy of Science Volume 2 ( Toronto: University of Toronto Press 1999) p. 143.

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  • 21

    Quoted from DrakeGalileo: Pioneer Scientist p. 108.

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    HobbesThomas White’s De Mundo p. 209.

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    HobbesDe Motibus Solis Aetheris & Telluris p. 443. I am very grateful to my colleague John M. Forrester for his invaluable help in translating Hobbes’s Latin verse.

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  • 36

    HobbesDe Motibus Solis Aetheris & Telluris pp. 443–444.

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    HobbesDialogus physicus pp. 377 379.

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    BoyleAn Examen of Mr T. Hobbes p. 134.

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    BoyleAn Examen of Mr T. Hobbes p. 134.

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    BoyleAn Examen of Mr T. Hobbes p. 133.

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    BoyleAn Examen of Mr T. Hobbes p. 134.

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    BoyleAn Examen of Mr T. Hobbes p. 134.

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    HobbesDialogus Physicus p. 355.

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    HobbesDialogus Physicus p. 359.

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    HobbesDialogus Physicus p. 361.

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    HobbesDecameron Physiologicum pp. 156–57. The explanation is hardly convincing but it is evidently trying to confine itself to mechanical principles (subsequent to the initiating of motions by God).

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