Descartes as Critic of Galileo

  • William R. Shea
Part of the The University of Western Ontario Series in Philosophy of Science book series (WONS, volume 14)


Descartes was born in 1596 a full generation later than Galileo and the two men never met. Galileo was seventy-three when Descartes’ first book appeared in 1637 and nowhere in his correspondence does he betray any awareness of the younger Frenchman’s existence even though Mersenne sent him a copy of the Discourse de la méthode. Descartes heard of Galileo, of course, for Galileo’s telescopic discoveries of 1610 created a sensation throughout Europe and were even celebrated in a public lecture at the College of La Flèche when Descartes was a student there. Descartes knew Italian, which was taught to their pupils by the Jesuits, but he does not seem to have read Galileo’s Italian works on hydrostatics, the sunspots and the comets that appeared between 1612 and 1623. Between 1623 and 1625, Descartes made an extended trip throughout Italy but he did not call on Galileo who at the time enjoyed the enviable possible of Mathematician and Philosopher to the Granduke of Tuscany. During that period Descartes was wrestling with problems of mathematics and optics and was only marginally interested in the astronomical phenomena that confronted Galileo.


Free Fall Simple Machine Virtual Velocity Impetus Theory Astronomical Phenomenon 
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  1. 1.
    Letter to Mersenne, April 1634, in C. Adam and P. Tannery, Oeuvres de Descartes 1897–1913. Reprint. Paris: Vrin, I. 286.Google Scholar
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  3. 3.
    Letter to Mersenne, 14 August 1634, A.T., I, 304. Beeckman thought more kindly of Galileo’s theory: “... puto earn rationem dignam esse consideratione et meis principiis nullo modo adversantem” (Isaac Beeckman, Journal 1604–1634 (ed. by C. De Waard), Vol. III, Martinus Nijhoff, The Hague, 1945, p. 171. Descartes outlines his tidal theory in chapter 12 of Le Monde (A.T., XI, 80–83) and in the fourth part of his Principia Philosophiae (A.T., VIII-1, 232–238). To Mersenne, he confided: “c’est une des choses qui m’a donné le plus de peine à trouver” (letter of November or December 1632, A.T., 1, 261).Google Scholar
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    Beeckman never saw that the principle of rectilinear inertia was incompatible with the assumption that circular motion was inertial. The following entry in Beeckman’s diary illustrates the nature of the confusion under which he, as well as Galileo, laboured. “Dictum est mihi hodie qui est dies 11 octob. 1629, Patrem Paulum Servitam Venetum sentire idem quod ego, ut ante saepe patet, de motu, videlicet quicquam semel monetur, id semper moveri nisi impedimentum accedat, eoque probasse aeternitatem motus in coelo a Deo semel motis” (Journal, Vol. III, p. 136). The Venetian Servite is Paolo Sarpi, Galileo’s friend during his stay in Padua. We see how the necessity of explaining the eternal revolution of the heavenly bodies led, in the absence of a mechanical theory such as Descartes’ or a theory of gravitation such as Newton’s, to a failure to grasp the implication of the law of inertia.Google Scholar
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    Compendium Musicae A.T., X, 97. Descartes also subscribed to the erroneous belief that the speed of sound was determined by its pitch: “Ce que vous dites que le son aigu s’étend plus viste que le grave est vrai en tout sens; car il est plus viste porté par l’air, à cause que son mouvement est plus prompt; et il est plus viste discerné par l’oreille... (letter to Mersenne, January 1630, A.T., I, 107).Google Scholar
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    Ibid., p. 308. Using Roemer’s determination of the speed of light, which gave eleven minutes as the time required for a ray from the sun to reach the earth, Huygens was able to show why the eclipses of the moon did not provide the reliable test that Descartes believed. (See A.I. Sabra, Theories of Light from Descartes to Newton, Oldbourne, London, 1967, pp. 203 ff.).Google Scholar
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    Letter to Mersenne, 11 October 1638, A.T., II, 382–383. In a letter to Galileo, 3 March 1635, Antonio de Ville solved the problem of the two concentric spheres much more clearly by printing out that the motion of the small circle is the outcome of two motions in the same direction, namely (a) the rotation of the small circle on itself, and (b) the motion of translation impacted to it by the large circle (Opere, XVI, 225–227).Google Scholar
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Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1978

Authors and Affiliations

  • William R. Shea
    • 1
  1. 1.McGill UniversityCanada

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