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Galileo's Claim to Fame: The Proof that the Earth Moves From the Evidence of the Tides

Published online by Cambridge University Press:  05 January 2009

W. R. J. Shea
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Extract

Until fairly recently a common way of doing history of science was to pick up an important strand of contemporary scientific thought and to trace its origin back to the philosophical tangle of the scientific revolution. This approach conveniently by-passed the breakdowns of once useful and pervasive theories, and neglected the long intellectual journeys along devious routes. History of science read like a success story; the pioneers who failed were neither dismissed nor excused; they were simply ignored. The historian knew what he was hunting for and he was careful to limit his search to areas where his quarry was sure to be found. This method, which has been dubbed the precursor-view, stands in contrast—albeit, not in opposition—to the contextual method, which aims at a better understanding of the actual thought-processes of the early scientists. On this second view, history of science must not only account for present theories in the light of past developments, it must also assess old theories in terms of the scientist's conceptual framework, and judge them against the background of the world picture of his age. This may lead the historian down the blind alleys of the past, chasing spurious attempts at explaining the nature of physical reality, but it can clear the ground for a less anachronistic interpretation of the emergence of modern science and the actual process of discovery. History of science acts as a winnowing fork, but we cannot suppose that the discoverer himself always separated the wheat from the chaff, and we must be ever wary of equating the dream with the task.

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Research Article
Information
The British Journal for the History of Science , Volume 5 , Issue 2 , December 1970 , pp. 111 - 127
Copyright
Copyright © British Society for the History of Science 1970

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References

1 Contextual history is not the same as the study of “science and society”, although it is very much concerned with the general climate of opinion and the existing social, political and economic structures. On the problems involved in any attempt to relate external and internal factors in the growth of science, see Hall, A. Rupert, “Merton Revisited or Science and Society in the Seventeenth Century”, History of Science, ii (1963), 1–17.CrossRefGoogle Scholar

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17 Fra Fulgenzio Micanzio in his life of Sarpi deplored “the loss of what the Father wrote on the motion of the water, for I am convinced that it would have given food to many intellects that go hungry without any hope of finding something that at least appears to satisfy them”. [Micanzio, Fulgenzio], Vita del Padre Paolo dell' Ordini de' Servi (Leiden, 1646), 105–106.Google Scholar

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22 Hans Geörg Herwart von Hohenburg expressed surprise that no one had treated ex professo of the motion of the earth, “cum argumenta praesertim Physica, quibus coarguatur motus terrae potius, quam stellis fixis, tribuendos esse, non deficiant pulcherrima, praesertim ex ratione Ventorum, maris per freta currentis uti et fluxus atque refluxus maris”. Kepler, Johann, Gesammelte Werke, ed. Caspar, Max (Munich, 1955), xiii, 178Google Scholar. Letter to Kepler, 12 March 1598. It is noteworthy that Galileo and Herwart were looking for the same thing: a physical proof of the motion of the earth.

23 Before 1616, we find numerous references to the projected “System of the World”, the “Great System”, or simply the “System” (e.g. Galileo, , op. cit. (2), xi, 286, 287, 370, 586Google Scholar; iii, 75, 96). After this date, Galileo spoke of the “Dialogue on the Tides (e.g. Ibid., xiii, 236, 247, 376; xiv, 54, 61, 66, 85). The idea of a Dialogue on the tides was not novel. Galileo might have got it from Ambrosio Florido's Dialogismus de natura universa Maris, ac eius genesi, et de causa fluxus, et reflexus eiusdem, atque de alijs accidentibus, quae eius naturarti comitantur. Interlocutores Philonauticus et Philosophus … Ad Illustrissimum, Excellentissimum Hippolytum Aldobrandinum (Pavia, 1613). Galileo does not mention this work, but it would be surprising if he had not heard of it since his friend Luca Valerio was closely associated with the Aldobrandini family, and Galileo himself corresponded with Card. Ippolito Aldobrandini (Ibid., xii, 431).

24 “I have not been able to obtain permission to mention the tides in the title of the book though it is the principal argument that I consider in my work.” Galileo, , op. cit. (2), xiv, 289Google Scholar. Letter to Elia Diodati, 16 August 1631.

25 The expression is Koestler, Arthur's in The Sleepwalkers (London, 1964), 458.Google Scholar

26 Sagredo acknowledged receipt of the Discourse on 12 November 1616. Galileo, , op. cit. (2), xii, 288–289.Google Scholar

27 Galileo sent his Discourse to Prince Leopold of Austria on 23 May 1618. Ibid., xii, 391.

28 Toby Matthew, writing from Brussels on 14 April 1619, informed Bacon that Richard White was on his way to London with a copy of Galileo's Discourse and that he would be pleased to show it to him. Ibid., xii, 450.

29 Bacon, Francis, op. cit. (2), i, 327; English trans., iv, 212.Google Scholar

30 Galileo, , Discourse of 1616, op. cit. (2), v, 378.Google Scholar

31 Mach, Ernst, The Science of Mechanics, trans, by McCormac, Thomas J. (6th edn.La Salle, Illinois, 1960), 262–264Google Scholar. The error in Galileo's theory is the mixing of two different frames of reference. Whereas the motion of the earth is considered relative to the sun, the resulting motion of the water is considered relative to the earth. But relative to the earth, the water can receive no acceleration due to the earth's annual motion, and the water must therefore be at rest relative to the earth. This non-technical criticism of Galileo's account was well within the compass of pre-inertial physics, and it was expressed as early as 1633 by Jean-Jacques Bouchard. Writing on behalf of a group of French physicists, he said: “They draw attention to a difficulty raised by several members about the proposition you make that the tides are caused by the unevenness of the motion of different parts of the earth. They admit that these parts move with greater speed when they descend along the line of direction of the annual motion than when they move in the opposite direction. But this acceleration is only relative to the annual motion; relative to the body of the earth as well as to the water, the parts always move with the same speed. They say, therefore, that it is hard to understand how the parts of the earth, which always move in the same way relative to themselves and to the water, can impress varying motions to the water. They entreat me to try to obtain from you some solution to their difficulty.” Galileo, , op. cit. (2), xiv, 251–252Google Scholar. Unfortunately, we do not know whether Galileo answered this query.

32 Galileo, , Discourse of 1616, op. cit. (2), v, 385.Google Scholar

33 Ibid., v, 386–387.

34 Galileo, , Dialogue on the Two Chief World Systems, op. cit. (2), vii, 455Google Scholar. In the English trans, by Drake, Stillman (Berkeley and Los Angeles, 1962), 429Google Scholar. Changes have been made in the translation for the sake of emphasis.

35 Ibid., vii, 456; Drake, S., op. cit. (34), 430.Google Scholar

36 Galileo, , op. cit. (2), xiii, 316–317Google Scholar. Letter to Galileo, 3 April 1626.

37 Ibid., xiii, 320. Letter to Cesare Marsili, 25 April 1626.

38 Galileo, , Discourse of 1616, op. cit. (2), v, 388.Google Scholar

39 Ibid., v, 389.

40 In the Dialogue, Galileo only gives instances of periods shorter than the six-hour one.

41 Galileo, , op. cit. (2), vii, 487Google Scholar; Drake, S., op. cit. (34), 462–463.Google Scholar

42 Ibid., vii, 443; Drake, S., op. cit. (34), 417.Google Scholar

43 Ibid., vii, 443; Drake, S., op. cit. (34), 417.Google Scholar

44 Ibid., vii, 443–444; Drake, S., op. cit. (34), 417.Google Scholar

45 Ibid., vii, 444; Drake, S., op. cit. (34), 418.Google Scholar

46 Ibid.

47 Ibid.

48 Ibid., vii, 445; Drake, S., op. cit. (34), 419.Google Scholar

49 de Dominis, Marcantonio, Euripus, seu de fluxu et refluxu maris sententia (Rome, 1624).Google Scholar

50 Galileo, , op. cit. (2), vii, 446Google Scholar; Drake, S., op. cit. (34), 420.Google Scholar

51 Ibid., vii, 463; Drake, S., op. cit. (34), 437.Google Scholar

52 Ibid., vii, 466; Drake, S., op. cit. (34), 440.Google Scholar

53 Giovanfrancesco Buonamici, writing from Madrid on 1 February 1630, explicitly informed Galileo of this fact. Galileo, , op. cit. (2), xiv, 75.Google Scholar

54 Galileo, , op. cit. (2), vii, 469Google Scholar; Drake, S., op. cit. (34), 443.Google Scholar

55 Ibid., vii, 470; Drake, S., op. cit. (34), 445Google Scholar. Cardano had remarked more than a century earlier, that no one could deny the influence of the moon and the sun and still account for daily experience: “Qui syderum influxum negant, hoc solum mihi respondeant velim, quonam pacto ratio haec tam subtilis quae experimento quotidie deprehenditur, aliter costare possit.” Cardano, Girolamo, De rerum varietate (Basel, 1557), 697.Google Scholar

56 Ibid., vii, 474; Drake, S., op. cit. (34), 449.Google Scholar

57 Antonio Rocco concluded his criticism of Galileo's theory of the tides by attacking him for paying lip service to sensory evidence and then contradicting experience. “At the beginning of your work, you often proclaim that you wish to follow the way of the senses so closely that Aristotle (who promised to follow this method and taught it to others) would have changed opinion, having seen what you have observed. Nonetheless, in the progress of the book you have always been so much a stranger to this way of proceeding that … all your controversial conclusions go against our sense knowledge, as anyone can see by himself, and as you expressly say yourself on page 325 [in op. cit. (2), vii, 355] speaking of Copernicus' theory, rendered plausible and marvellous to many by abstract reasoning although it is against all sensory experience.” Rocco, Antonio, Esercitationi Filosofiche in Galileo, op. cit. (2), vii, 712.Google Scholar

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59 Ibid., vii, 475; Drake, S., op. cit. (34), 449–450.Google Scholar

60 Ibid., vii, 477; Drake, S., op. cit. (34), 452.Google Scholar

61 Ibid., vii, 478; Drake, S., op. cit. (34), 453Google Scholar. This passage has recently been adduced by Harold L. Burstyn as evidence that Galileo was the first to point out that the earth's orbit around the sun is not described by the centre of the earth but by the centre of mass of the earthmoon system. According to Burstyn, Galileo “shows clearly, by an argument similar to that for the falling body, that the earth and the moon—if in some dynamic relation—must revolve about a point which we call their common centre of mass”. Burstyn, Harold L., “Galileo's Attempt to Prove that the Earth Moves”, Isis, liii (1962), 179Google Scholar. Burstyn's interpretation is open to criticism on the grounds that the analogy directly invoked by Galileo is not the pendulum but the movable lead-weight in the wheel-clock. See Aiton, A. J., “On Galileo and the Earth-Moon System”, Isis, liv (1963), 265–266.CrossRefGoogle Scholar

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63 Ibid., vii, 481; Drake, S., op. cit. (34), 455–456.Google Scholar

64 G. B. Baliani found that Galileo explained everything very clearly “except the last discussion on the irregularities in the additions and substractions of the diurnal and annual revolutions”. Ibid., xiv, 343. Letter to Galileo, 23 April 1632. Francesco Rinuccini also failed to see how the diurnal motion could produce greater tides at the equinoxes. Ibid., xvii, 227. Letter to Galileo, 28 November 1637.

65 Bacon, Francis, op. cit. (2), iii, 47Google Scholar; English trans., v, 443.

66 Riccioli, G. B., Almagestum novum (Bologna, 1651), 380.Google Scholar

67 Galileo, , op. cit. (2), vii, 483Google Scholar; Drake, S., op. cit. (34), 460.Google Scholar

68 Ibid., vii, 486; Drake, S., op. cit. (34), 461–462Google Scholar. In the Dialogue, Galileo did not give any reference, but in a letter to Cesare Marsili, 20 March 1632, he mentioned Cesalpino and Origano. Ibid., xiv, 334–335. Origano affirmed the daily rotation of the earth on its axis but he denied the orbital revolution around the sun. Origano, D., Ephemerides (Frankfurt, 1609), 2vGoogle Scholar of the Introduction.

69 Ibid., vii, 486; Drake, S., op. cit. (34), 462Google Scholar. In the margin, Galileo referred to the Greek mathematician Seleucus, and in a letter written shortly after the publication of the Dialogue, he commented as follows, “I received the Discorsi of the Signor Roffeni [A. Favaro was unable to find this work] several days ago … See the place where the Signor Roffeni honours me by putting me on the same footing as the ancient mathematician Seleucus in the study of the cause of the tides. I am glad that I chanced to agree with the opinion of such a great philosopher. This will add weight to the theory. However, I should have thought that I was the first to entertain the idea, I do not say of locating the cause of such an effect in the motion of the earth, but of doing so in such a way that the effect might follow, and not in such a way that it bears no relation to it whatsoever as Origano and Cesalpino have done, and perhaps Seleucus himself if we could know how he arrived at it. For attributing to the earth a simple and uniform motion cannot cause such a change in the sea”. Ibid., xiv, 334–335. Letter to Marsili, 20 March 1632.

70 Ibid.

71 Ibid., vii, 486–487; Drake, S., op. cit. (34), 462Google Scholar.

72 I have only found one author who held that the tides were unequal at new and full moon. This is Cesalpino, who believed that the tides were greater at full moon, the reverse of what Galileo's theory entailed. See Cesalpino, Andrea, op. cit. (5), 70r.Google Scholar

73 Galileo, , op. cit. (2), xvii, 214–215.Google Scholar