The Reception of Newton’s Gravitational Theory by Huygens, Varignon, and Maupertuis: How Normal Science may be Revolutionary Ko ffi Maglo Massachusetts Institute of Technology . . . The discrimination of normal from revolutionary episodes demands close historical study, and few parts of history of science have received it. One must know not simply the name of the change, but the nature and structure of group commitments before and after it occurred. Often, to determine these, one must also know the manner in which the change was received when rst proposed” Thomas Kuhn (1970, p. 251). This paper rst discusses the current historical and philosophical framework forged during the last century to account for both the history and the epistemic status of Newton’s theory of general gravitation. It then examines the conict surrounding this theory at the close of the seventeenth century and the rst steps towards the revolutionary shift in rational mechanics in the eighteenth century. From a historical point of view, it shows the crucial contribution of the Cartesian mechanistic philosophy and Leibnizian analytic methods to the emergence of so-called Newtonian mechanics which can also be fairly characterized as a synthetic theory of attraction. From a philosophical standpoint, the paper suggests that the reworking of Newton’s theory in the 18th century is better understood in a theoretical framework that reconciles Kuhn’s notion of “invisible revolution” rather than his notion of “normal science” with Whewell’s ascription of the completion of dynamical studies to the post Newtonian period. Introduction The question of when the new way of investigating nature, the so-called Scientic Revolution begun by Copernicus reached its completion is still a lively debate among historians. Some argue that it culminated with the publication of Newton’s Principia in 1687 (Westfall 2000).1 Others main1. Richard Westfall (2000, p. 48), for example, wrote: “In any event, with Newton the Perspectives on Science 2003, vol. 11, no. 2 ©2003 by The Massachusetts Institute of Technology 135 136 The Reception of Newton’s Gravitational Theory tain that the narrative itself of the Scientic Revolution emerged only in Enlightenment texts combined with a partial selection of what came to be seen as the positive aspect of Newton’s achievement (Dobbs [1994] 2000; Jacob 2000; Osler 2000).2 This historical issue has a bearing on philosophical appraisal of scientic progress and vice versa. In this paper, I argue that to solve this problem we need to return to William Whewell’s assessment of the relationship between Newton’s Principia and Laplace’s Mécanique céleste (Whewell 1823). A suitable philosophical tool to achieve this is Thomas Kuhn’s notion of invisible revolution (Kuhn 1962). This however entails the abandonment of Kuhn’s own account of scientic progress in the eighteenth century in terms of normal science. 3 The background assumption of this reading of Kuhn against Kuhn is that where Kuhn saw a slow conversion in post revolutionary periods I see a slow revision culminating in substantial changes. It is this notion of gradual but decisive transformations of scientic theories that Whewell’s assessment, as we shall see below, implies. Indeed, before the Principia was accepted in key scientic institutions on the Continent, it underwent a crisis followed by a deep revolutionary transformation. Accordingly, it is useful to suggest here a periodization for new science and the new philosophy of nature found their denitive form in which they shaped the scientic tradition . . .” Westfall’s paper, published posthumously, is a reaction to Dobbs’ reassessment of the concept of Scientic Revolution; see below. 2. Casper Hakfoort (1988) also stated the idea of the incompleteness of the Scientic Revolution. However, Dobbs (2000) took issue with the concept of Scientic Revolution, usually understood as “a change that is sudden, radical, and complete.” The concept, she said, is anachronistic and inappropriate as applied to Newton as well as Copernicus. For her, the patterns of Newton’s thought differ more signicantly from ours than is traditionally believed. She observed that the shaping of Newton’s reputation as the “father of modern science” is due to the decline of alchemy in the eighteenth century. Therefore, the narrative of the Scientic Revolution, except for “its dramatic capitalized title,” she believed, emerged plainly in d’Alembert’s philosophical writings in the same period. Accordingly, she considered the problem of delimiting the Scientic Revolution to be a historical one. Dobbs’ position depends on studies of Newton’s relationship with alchemy and theology (Dobbs 1975, 1991; Westfall 1980; J. E. McGuire and P. M. Rattansi 1966). Also, Margaret C. Jacob (2000, p. 319) systematically historicized the narrative of Newton’s accomplishments and like Dobbs, directed her criticism against the current understanding of the Scientic Revolution based on the assumption that “the heroes had to be pure, simply great ‘scientists,’ and they alone made it happen.” As Margaret J. Osler (2000, p. 5) has pointed out, the result of Jacob’s “exercise in historicizing the history of science” is to suggest a radical rethinking of the Scientic Revolution. It was constructed in the eighteenth century when scientists privileged the positive aspect of Newton’s achievement. 3. According to Thomas Kuhn, the making of science has to be divided in two: A revolutionary shift of paradigm and “normal science.” The latter is essentially a period of solving puzzles within the limits of a given paradigmatic framework. A change of paradigm is the principal element in a scientic revolution. Perspectives on Science 137 the history of so-called Newtonian mechanics. One should distinguish at least four stages: a period of discovery that ended in 1687; a period of eclipse 4 during which Huygens, Leibniz, and the Cartesians rejected Newton’s theory of general gravitation, but Varignon strengthened the Principia as a mathematically based work; a period of revision, from the 1730s to the 1760s, when Maupertuis, Euler, d’Alembert, Clairaut, and to some extent the Bernoullis, reinterpreted the new physics; and a period of standardization when Lagrange and Laplace codied “Newtonian” mechanics in its denitive form. In what follows, I rst provide a theoretical framework, let’s call it the W-K bridge, suitable to account for scientic progress in the eighteenth century by connecting Whewell’s idea of the completion of the Scientic Revolution in Laplace’s work with Kuhn’s notion of invisible revolution. Second, I describe the complex process of theory appraisal that opposed Newton to his Continental peers at the close of the seventeenth century. Then I proceed to analyze some of the chief roots of canonical “Newtonianism.” 1. Accountin g for scientifi c growth in the eighte enth centur y As early as 1823, Whewell wrote: “The student who feels a proper admiration for the system of the Principia, ought to look forward to a complete development of it in the Mécanique céleste . . .” (Whewell 1923, preface). According to Whewell, the Mécanique céleste of Laplace rather than Newton’s Principia brought the study of dynamics to its completion. Among those who cleared the way for such an achievement, he particularly admired Leonhard Euler, a mathematician of the Basel school. This rating of Laplace’s Mécanique céleste and Newton’s Principia disturbed some scholars in the twentieth century because it contrasted with the new historical and philosophical trend. John Herivel (Whewell 1967, p. xv), for one, characterized Whewell’s attitude as temerity and stated his own view as follows: “With certain notable exceptions, the whole history of dynamics from Newton to Einstein can be thought of as an exploitation, albeit innitely 4. Julian Huxley ([1942] 1964; Bowler 1983) used the term “eclipse of Darwinism” to characterize the crisis surrounding Darwin’s theory at the turn of the twentieth century. During this period, evolution was accepted while natural selection sparked controversial debate. Similarly, at the turn of the eighteenth century, the fact that Newton had successfully demonstrated the validity of Kepler’s laws by use of the inverse square law was generally acclaimed. But attraction was sharply rejected in key scientic institutions on the Continent because it was considered an incoherent physical concept, incapable of describing the mechanism of nature. Mendelian discoveries were required to lead the theory of evolution to a new synthesis. Likewise, Leibnizian discoveries were needed to save the theory of general gravitation from declining and to lead dynamics to completion. 138 The Reception of Newton’s Gravitational Theory ingenious and resourceful, of the denitions, principles and propositions in the Principia” (Herivel 1965, introduction). Relying on similar assumptions, some scholars in the twentieth century did not seem to nd critical changes between Newton and his immediate followers. 5 The problem with this position is that it is at odds with theoretical frameworks often applied in the evaluation of scientic achievements such as Copernicus’ and Newton’s theories. For example, I. Bernard Cohen (1985) interestingly stressed the fact that the Copernican revolution was not Copernicus’; as with many other revolutionary ideas, it was only through the works of such later revolutionaries as Kepler and Galileo that the Copernican revolution truly occurred. This points to the soundness of Kuhn’s emphasis on the invisibility of scientic revolutions. Kuhn argued that a revolution consists of a particular change that is not necessarily a modication on a large scale. Thus, small revolutions occur more often than is usually believed and lie in the reformulation of the tradition of a given scientic community. Revolutions can even be invisible to their authors. Referring to Newton’s attribution of his own second law of motion to Galileo, Kuhn (1962, pp. 139… 40) wrote: “. . . Newton’s account hides the effect of a small but revolutionary reformulation in the questions that scientists asked about motion as well as in the answers they felt able to accept . . .” For Kuhn, these kinds of invisible revolutions that alter questions and answers, rather than introduce new empirical evidence, signicantly explain scientic development. They bring about conceptual reconstruction and modications in a group’s commitments, i.e., symbolic generalizations, ontological and heuristic models, and exemplars or paradigms (Kuhn 1977, pp. 293… 319). Curiously, Kuhn (1962, p. 33) did not seem to heed his own creed about invisible revolutions and, unlike Whewell, he saw the generations of physicists from Euler and Lagrange to Hamilton, Jacobi, and Herz as generations of normal scientists whose works produced no revolutionary changes in the Newtonian paradigm. Though Kuhn’s account of scientic growth, particularly in the eighteenth century, accords well with that of many contemporary historians and philosophers, there are good reasons both historical and philosophical to depart from it. Indeed, mid-eighteenth century scientists tend to view their own achievements as constituting un5. For example, Alexandre Koyré (1968, pp. 42… 3) emphasized Newton’s responsibility rather than that of Newton’s followers in the process of achieving a mechanistic worldview. Newton’s science, he believed, created the enigma of modern man and woman “by substituting for the world of qualities and sensible perceptions—the world in which we live, love and die—a world of quantities stemming from the deication of geometry.” See also I. Bernard Cohen (1980, 1982) about “The Newtonian style,” which scientists would have followed since the end of the seventeenth century. Perspectives on Science 139 precedented progress in the history of science. 6 Moreover, as Niccolò Guicciardini (1999, p. 6) recently put it rather bluntly, following extensive studies of Newton’s mathematical achievement: “After Euler the Principia’s mathematical methods belong denitely to what is past and obsolete.” It is rather the “Eulerian mathematical style” or precisely his “calculus and mechanics,” Guicciardini argued, that in the end proved to be the most progressive way to solve problems in dynamics. This mathematical reworking of mechanics “in its own right,” observed George Smith (2002b, p. 57), “is no small contribution to the science coming out of the Principia.” Earlier, Clifford Truesdell (1970) similarly contested the idea that eighteenth century scientists were merely Newtonians whose work consisted primarily of simply applying Newton’s laws. He argued that rational mechanics, along with its philosophy of nature, grew as a response to a challenge stemming from Newton’s failures, errors and guesswork in the Principia. The great architect of the success of rational mechanics, he said, was Euler. He stressed that what is termed today “Newtonian mechanics” is rather the result of Euler and Lagrange’s achievement, and that it bears very little direct relationship to the Principia. He maintained that the Basel mathematicians, for example, were far from being Newton’s disciples. On the contrary, these savants began “as doubting opponents, who accepted, grudgingly, only some isolated results. Newton’s achievement, great though it was, was far from enough to cause the revolution in scientic thought historians of the last century and ours have been pleased to imagine” (Truesdell 1970, p. 201). Not only does this emerging historical trend tend to vindicate Whewell, but even more important it involves what one may term “the rediscovery of Euler” or simply, to avoid reductionism, “the rediscovery of the eighteenth century’s invisible revolution.” This invisible revolution, I would like to argue, is the result of a triple dissociation from Newton’s legacy mainly by Continental mathematicians and physicists in the Leibnizian, Huygenian, and Cartesian circle. These Continental revolutionaries, as I shall call them here, parted company with Newton on the specic issues of which conceptual frameworks (ontological dissociation), mathematical techniques (methodological dissociation), and scientic standards and values (philosophical dissociation) were suitable to put forward in mechanics. 6. D’Alembert, for example, conceived of his Traité de dynamique ([1743] 1758) as a turning point in history of science while Euler wrote to Clairaut in 1751 praising, certainly with some exaggeration, the resolution of the lunar crisis as a mathematical success without precedent in history (Birgoudan 1930, pp. 26… 40; Hankins 1970, p. 35). 140 The Reception of Newton’s Gravitational Theory The roots of this triple dissociation, as we shall see below, lie in the clash of giants prompted by the publication of the Principia at the close of the seventeenth century. Yet the magnitude of the clash and the erce debate it sparked has not been fully appreciated. A closer scrutiny reveals that what was at stake was not only whether or not attraction is a mechanistic concept (or even intelligible). Rather, the conict went deeper and apparently concerned even the very standards of scientic rationality. After a period of eclipse, Newton’s achievement in the Principia, as I will argue below, underwent a deep revision on the Continent that allowed its subsequent standardization by Lagrange and Laplace. Not all Newtonian roads led to Laplace. Take for example Newton’s laws of motion. By the middle of the eighteenth century, Newton’s concept of inertia, understood as vis or the force inherent to bodies, had become outlandish to the Continental revolutionaries. Jean Le Rond d’Alembert ([1743] 1758) saw Newton’s vocabulary in the denition of this law, among other things, as very obscure. He set as a fundamental goal to “expel” force from bodies and to change its status and conceptual meaning. Accordingly, he formulated his own three laws of motion “leaving off motive causes in order to focus only on motion as their effects; thus I completely banished from science the conception of forces inherent to bodies in motion. These forces are nothing more than metaphysical and obscure beings that plunge a science which is clear by itself into darkness” (D’Alembert 1758, p. xvij). Inherent forces and motive causes are key to Newton’s conceptual apparatus. But d’Alembert rejected them as obscure metaphysical entities and, to use Baconian terminology, epistemological impedimenta. Yet he did not deem it necessary to prohibit the word “force” from science. Then what became of force in his approach? It is shorthand or, as he stated it, it is an “abbreviated manner of expressing a fact” (D’Alembert 1758, p. xix). Its status and relationship to body are quite similar to those of velocity: velocity, he asserted, is by no means inherent in body. So, from a philosophical point of view, when d’Alembert claimed for example to “follow Newton in using the name ‘force of inertia’ ” to characterize the properties bodies have to remain in the state they are, he was not at all standing within the same theoretical framework as Newton. They did not share the same ontology and scientic values. 7 7. However, Cohen (2002, p. 62) thinks that Newton’s followers did not have any problem with Newton’s denition of inertia and, as an example of this smooth acceptance, he refers to d’Alembert. In fact, Cohen (Newton 1999, p. 60) believes that Newton successfully eliminated from the Principia any signicant tracks of the alchemical origins of his discoveries in such a way that it took three hundred years to get behind the façade of his book. But Newton’s opponents, particularly Leibniz ([1715] 1973, pp. 37… 40; 1965, Perspectives on Science 141 In fact, d’Alembert wanted to axiomatize mechanics (apparently the mechanics of solid bodies) and his scientic standards and values, heavily inuenced by Cartesian philosophy (Hankins 1970; De Gandt 2001), could not tolerate the intrusion of metaphysical entities into this undertaking. His criticism of his predecessors, Newton included, was that they were primarily concerned with building the “scientic edice” (solving problems) while neglecting its foundations (the theoretical issues). As a result of this negligence, thorny problems arose in mechanics, sparking erce and fruitless debate. D’Alembert’s Traité de dynamique indeed aimed at 1) establishing a new rational basis for mechanics by reducing scientic principles to just a few and 2) at providing physics with a new method of solving problems, the so-called d’Alembert’s principle. These two goals are so closely related, d’Alembert believed, that he proposed to achieve one by the other. In this setting, Newton’s conceptual tools and scientic values became irrelevant. Thus d’Alembert’s raising of questions of theoretical foundations is not easy to reconcile with Kuhn’s notion of normal science. In the same vein, Euler (1768) expressed frustrations about the theoretical background assumptions of the Principia. He viewed Newton’s language in the denition of inertia, for example, as truly risky. To escape what he perceived as a naïve theoretical framework, Euler pointed out that inertia is by no means a force. He parted company with Newton regarding the class of facts that should be accounted for under the terminology of force.8 In Kuhnian terminology, Euler and Newton did not perceive the same thing when talking about rectilinear uniform motion of a body; they held incommensurable views. In short, Continental revolutionaries were far from being normal scientists, à la Kuhn. They were making an invisible revolution. John L. Greenberg (1995) also reached the same result recently, and concluded after studying the specic matter of the earth’s shape that Kuhn’s categories of normal science cannot account for the development of physics from Newton to Alexis Claude Clairaut. p. 417) already seemed to characterize Newton’s concept of attraction as an obscure entity. For about a half century, Cartesians fought against the metaphysical assumptions of the Principia (Brunet 1970; Guerlac 1981). 8. Besides his Letter LXXVI to a princess of Germany, Euler (1750) had indeed pursued Newton’s mathematical work in reformulating Newton’s second law in algebraic terms, f ma; he published a differential version as df a dm. He distanced himself more overtly from Newton on several other points. He maintained, for example, that attraction is a result of the impulse of the subtle uid surrounding all bodies. Just as he followed Cartesian philosophy in the physical description of, let us say, the fall of an apple, he observed that “force of inertia” is a misnomer, since force is the opposite of the quality of a body remaining in a state of rest or motion. In the new Eulerian framework, force is strictly what changes the state of bodies. 142 The Reception of Newton’s Gravitational Theory Now, if a scholar favors other philosophical terminology he or she can rightly reply that in spite of the philosophical and ontological dissociations with the Principia, Continental revolutionaries were still working within Newton’s program of research. That might mean, in Imre Lakatos’ terms (1970), for example, that Newton’s theory contained an irrefutable “hard core” dened by the three laws of motion and the law of general gravitation. For any Newtonian, dealing with any kind of problem, these laws could not be altered. 9 This however does not seem to be in agreement with the facts. D’Alembert changed some of Newton’s laws of motion as suggested above. Through systematic revision, reformulation and substitution, he proposed as his own three laws the law of inertia, the law of composition of motion, and the law of equilibrium. But in the end all these laws seem to be reduced to a single fundamental law of equilibrium (D’Alembert 1758). Moreover, during the lunar apogee crisis, Alexis Claude Clairaut (1749, pp. 334… 7) declared himself very dissatised with Newton’s theory and resolved to accept nothing from Newton henceforth. He cast doubt upon the universal validity of the inverse square law, preferring “to investigate directly the determination of the celestial movements on the sole supposition of their mutual attraction.” He bypassed Newton’s law. Actually, Clairaut still admitted attraction as a working hypothesis. But, during the crisis years, he abandoned his previous enthusiastic and holistic defense of Newton’s laws. From a philosophical point of view, what does Clairaut’s boldness demonstrate? It shows 1) that there was no methodological decision on the part of Newton’s followers to keep Newton’s laws unchanged when anomalies occurred, and 2) that scientists could question even the inner core of their eld or research program.10 From an historical 9. Lakatos (1970, p. 133) wrote: “In Newton’s programme the negative heuristic bids us to divert the modus tollens from Newton’s three laws of dynamics and his law of gravitation. This ‘core’ is ‘irrefutable’ by the methodological decision of its protagonists: anomalies must lead to changes only in the ‘protective’ belt of auxiliary, ‘observational’ hypothesis and initial conditions.” 10. Kuhn (1962, p. 81) underrated the importance of attempts to change Newton’s gravitational law during this crisis. He contended that these claims were not of great importance. Yet Clairaut, who demonstrated in the 1750s that the crisis arose from a mathematical error, appealed for a radical modication of Newton’s gravitational law in the 1740s. Clairaut’s proposal fostered sharp debate in the French Academy. In the late 1740s, Euler also became skeptical about the universal validity of Newton’s law. When Lakatos (1978, pp. 193… 222) became aware of these refutations of his philosophy in a paper (published posthumously), he seemed disarmed and simply contended that Newton’s methodology supplies no answers for the philosophical questions raised by the behavior of such scientists as Clairaut, Euler, and Poincaré. Perspectives on Science 143 point of view, it shows how Newton’s immediate followers on the Continent were rather skeptical “disciples” keen to innovate. Euler’s Mechanica (1736) clearly indicates the demand for innovation felt by the Continental revolutionaries. Euler was not only frustrated by the theoretical assumptions of the Principia but also by the mathematical methods used by Newton. According to him, though the reader of Newton’s book may be convinced about the accuracy of Newton’s ndings, he or she “cannot understand them clearly and distinctly” and, moreover, cannot nd in the synthetic method of uxions used by Newton tools to solve problems just slightly different from those resolved in the Principia. Euler (1736) wrote in his preface: “. . . This was in fact my own experience when I undertook a detailed study of Newton’s Principia . . . Although I somewhat understand the resolution of several problems, I was unable to solve problems just a bit different . . .” There is no more elegant way to say that Newton’s Magnus Opus, undoubtedly a marvelous achievement, did not however supply appropriate heuristic methods and exemplars or paradigms for solving problems acceptable to the Continental revolutionaries. Thus, what I call a W-K bridge is a conceptual framework that allows us to acknowledge that many scientic theories, e.g., general gravitation and evolution, are born incomplete but grow by revolutionary transformations. It provides not only a historical description of the process of transformation but also a philosophical assessment of the change. In this instance, it makes perceptible and intelligible the Continental revolutionaries’ ontological, methodological, and philosophical dissociation from Newton. To further illustrate this triple dissociation, I have chosen to focus here on Varignon and Maupertuis. I postpone the cases of Euler, Clairaut, and d’Alembert to another occasion.11 However, to strengthen the idea of a period of eclipse that I have introduced here apropos the appraisal of the history of the Principia, I shall show how some noteworthy Continental mathematicians perceived this book from the very beginning. According to Kuhn, to discriminate a normal from a revolutionary change, it is important to know how the revolutionary change was perceived when it rst occurred and what became group commitments, if any, among the proponents of the change. 2. Another “sup reme mathema tician” reacting to the Principia Derek T. Whiteside (1970, p. 6) once remarked that in Newton’s lifetime only Christiaan Huygens, Gottfried Wilhelm Leibniz, Pierre Varignon, 11. For more details, see my article “The Rise of Newtonian Mechanics, or the Hidden Revolution of Euler, d’Alembert, and Clairaut,” in progress. 144 The Reception of Newton’s Gravitational Theory Abraham De Moivre and Roger Cotes were able to penetrate the technical content of the Principia. But what is striking is that the only physicists who were unquestionably Newton’s peers on that list were to Newton what Albert Einstein, Louis De Broglie and Erwin Schrödinger, among others, would later be to the school of Copenhagen-Göttingen. Leibniz and Huygens were never able to accept the theoretical framework of Newton’s oeuvre. The case of Huygens is particularly interesting for at least three reasons. First, unlike Leibniz, he did not seem to be involved in personal quarrels with Newton. Second, from 1666 on, the young French Academy depended on his intellectual assistance. There can be no doubt that he contributed greatly to its ourishing. This scientic institution, along with the Basel mathematical school, was an active agent in revising Newton’s science. Third, Leibniz referred to Huygens when he wrote to Newton about the Principia. He called Newton’s attention to the work of “Christiaan Huygens, that other supreme mathematician,” as a possible way of completing the Principia. 12 But there is more. Newton himself recommended Huygens’ Horologium oscillatorium to Richard Bentley as a work “that will make you much more ready” to understand the Principia (Newton 1961 vol. 3, pp. 155… 6). Likewise, Huygens greatly hoped to see a revised version of the Principa (OCCH vol. 10, p. 209)13 and even acknowledged for example that Newton’s treatment of motion in resisting media was superior to Leibniz’ and his own work on the subject (OCCH vol. 9, p. 367). Both men indeed showed great interest in the work of the other, and some scholars have even suggested that the Horologium oscillatorium might have served “as a model” for the Principia despite the innovative style of the latter (Guicciardini 1999, pp. 30, 128). All in all, Huygens’ attitude towards the Principia provides reliable clues for assessing the reception of Newton’s achievement on the Continent at the close of the seventeenth century. This attitude can be described in a sequential form as follows. Act one: skepticism and caution. Before he received a copy of the Principia, Nicolas Fatio de Duillier (OCCH vol. 9, p. 167), in a letter of June 24, 1687, provided Huygens with a brief account of the philosophy of nature encompassed by the book. Fatio reported that Newton’s work bypassed Cartesian philosophy. In his response to Fatio on July 11 of the same year, Huygens adopted an attitude of prudence. He wrote simply, 12. “. . . I do not doubt,” Leibniz wrote to Newton, “that you have weighed what Christiaan Huygens, that other supreme mathematician, has remarked, in the appendix to his book, about the cause of light and gravity . . .” (Newton 1961 vol. 3258, my emphasis). 13. OCCH Oeuvres complètes de Christiaan Huygens. Perspectives on Science 145 but interestingly: “I want to see Newton’s book. I am willing to admit he is not Cartesian so long as he does not make suppositions like that of attraction” (OCCH vol. 9, p. 190). Huygens sharply drew the limits of scientic acceptability: one can be anti-Cartesian; however, scientic achievement has some requirements that one cannot get around. Act two: astonishment and admiration. When he read the Principia in 1688 Huygens exclaimed: “See all the difculties that the celebrated Mr. Newton has made to disappear along with the Cartesian vortices; and he has taught us that the planets are kept in their orbits by gravity. And that the eccentrics must necessarily become elliptic gures” (OCCH vol. 21, p. 143). Huygens was astonished to see that Newton had solved all the problems relative to Kepler’s laws. He was so impressed that towards the close of the same year he asked his brother Constantine, who had just arrived in England, to assist him in meeting the “celebrities” of the Royal Society once again. Huygens particularly desired to meet Newton. He stated: “I admire greatly the beautiful discoveries that I nd in the work he has sent me” (OCCH vol. 9, p. 305). The beautiful discoveries concerned mathematics. 14 Act three: regret and confession. Huygens then declared that he had long had the intuition that the spherical gure of the sun and of the earth could be produced by the same cause. But still having the Cartesian vortices in mind, he could not generalize the action of gravity. Huygens then stated that he had nothing against attraction as long as Newton did not afrm that it acts from an inherent quality of matter (OCCH vol. 21, pp. 472… 4). Act four: incomprehension and rejection. A year later, on November 18, 1690, Huygens asserted in a letter addressed to Leibniz that attraction is an absurd principle and that he did not admit the theories Newton built on it. Attraction is unacceptable since it is, in all its forms, inexplicable by the principles of mechanics and the laws of motion. Consequently, Huygens confessed that he was deeply perplexed that Newton was able to build so much research and such difcult calculations on such a weak theoretical foundation (OCCH vol. 9, p. 538).15 14. According to Marie Boas Hall (1980, p. 78), direct contact with Newton in 1689 and the study of the Principia may have furnished Huygens with the necessary stimulation to complete the Traité de la lumière. They may also have reinforced the conviction he expressed a year before about the validity of the elliptic orbit of the planets dened by Kepler’s rst law. Whiteside (1964) stressed the fact that Newton himself at rst accepted only with hesitation Kepler’s rst two laws. 15. However, Huygens, at several occasions, stated his strong opposition to the use of the concept of attraction in science. See for example his letter to Hudde (OCCH vol. 9, p. 267) or to Guillaume de l’Hospital (OCCH vol. 10, p. 354). Thus the chronology of the correspondence as a whole is not crucial to my story. 146 The Reception of Newton’s Gravitational Theory The case of Huygens demonstrates that Newton’s Principia, though clearly a mathematical work of genius, was not compelling for Continental mathematicians and physicists because, compared against Cartesian scientic standards and values, it depended on incoherent physical concepts. In contrast to the general acceptance of Newton’s theory in England, Continental mathematicians, physicists and philosophers were in the end reluctant to endorse it as a whole. This allows us to distinguish among several kinds of interpretations and among the different degrees and kinds of support accorded to Newton’s theory in different countries, scientic institutions, disciplines, and time periods. Huygens’ denitive position is only favorable to Newton’s mathematical ability. But when it came to the progress of physical science as a whole, the appraisal of Newton’s theory in signicant part stumbled against the theoretical bases of the Principia. How to understand Huygens’ problem? Cohen put forward an interesting idea that might explain it. According to him, Huygens’ problem stemmed from failing to understand Newton’s scientic style. This style allowed Newton to employ a purely mathematical treatment of nature, yielding an idealized result that could then be subjected to the verdict of experiment. Cohen (1980, p. 81) wrote: ‘‘Hugyens, disturbed by the intrusion of the concept of attraction, failed to discern that this term appears primarily towards the end of bk. one of the Principia, where Newton is still concerned with mathematics rather than with physics, with what I have chosen to call here a mathematical construct, and not with physical reality. This was a distinction that Huygens himself was not able to make, or was not willing to make . . .’’ We shall return to the interest of Cohen’s description of Newton’s methodology later. But Huygens’ problem appears to be a complex one involving both theoretical and empirical considerations.16 In the Discours de la cause de la pesanteur (OCCH vol. 21), for example, Huygens seems to indicate that his reasons for pursuing the discussion about the shape of the earth is that empirical data lend support to his theoretical anticipations. If so, I would like to try to articulate an alternative explanation to Huygens’ problem. It is possible that Huygens would still have opposed Newton even if he had made a distinction between mathematical construction and physical reality in the Principia. Moreover, Newton himself has been unable to provide a “positivistic” defense of his masterpiece. For example, in the general Scholium of the 1713 edition of the Principia, Newton stated that he had not yet assigned a cause to gravity (“sed causam gravitatis nondum assignavi”). This indicates that the adjustment of the theoretical framework of his theory was still a relevant task for him. The fact is that at 16. See for example Huygens’ letter to Hudde in (OCCH vol. 9). Perspectives on Science 147 the end of the seventeenth century the aim of physicists, Newton included, was not mathematical calculation and experimental proof only, as it would be the case in the post Comtian positivistic era. Their aim seems to be that of judging whether the descriptive terms and the basic concepts used in a physical explanation adequately represent the phenomena to which they refer, and whether the calculations attached to them give an exact account of the phenomena as shown by experiment. It is in this connection that Huygens, Leibniz and the Cartesians thought that Newton had failed and that therefore physical explanation, and consequently mechanics as such, remained a task still open before them. Huygens’ problem seems to arise from a radical opposition between two different perceptions of scientic practice though, as mentioned earlier, empirical considerations might also have played a role.17 For him, the scientic explanation of the “secret mechanisms” of nature must utilize only “mechanical arguments,” that is to say, considerations of shape and motion in the Cartesian style. To do otherwise would be to abandon all hope of understanding anything at all in physics (OCCH vol. 21, p. 446). For Cartesians, the framework of science is delimited by the use of concepts with mechanical meanings. All natural phenomena must be explained in terms of impact or contact between bodies: the shock of their contact generates motion. The dynamical properties result only from the impenetrability of matter. On the Continent, the perception of scientic practice rested on a kind of aprioristic rationalism. By contrast, for Newton (1687), who intended to develop mathematics in relation to natural philosophy,18 rational mechanics consists rst of all in starting from experiment or observational propositions of general import based on the nature of things.19 Then it consists in submitting the results to mathematical treatment, and, nally, in relating the mathematical results to natural phenomena.20 Query 31 of the Opticks also dened this procedure with the qualication that it consists in starting from experiment, or from other certain Truths.21 From the beginning of the Principia, 17. See E. Schlisser and G. Smith, “Huygens’s 1688 Report to the Directors of the Dutch East India Company on the Measurement of Longitude at Sea and the Evidence it Offered Against Universal Gravity” (to be published). According to Schlisser and Smith’s reconstruction, “Huygens had cogent empirical reasons to reject Isaac Newton’s theory of universal gravity . . .” I thank the authors for generously sending me their manuscript. 18. See the preface. 19. See particularly Book 3, Rule IV. 20. See Book 1, Proposition 69. 21. But which ones? It is not certain that it is here a case of modern scientic laws, but rather of truths of the prisca sapientia. Newton in his De systemate mundi for example believed that heliocentrism and his own inverse square law belong to this tradition (See also Newton 1961 vol. 3, p. 193). 148 The Reception of Newton’s Gravitational Theory Newton afrmed that geometry is a branch of mechanics, on which the description of mathematical gures depends. In one of his letters to Oldenburg, he stressed that the mathematical sciences depend just as much on physical principles as on mathematical demonstrations (Newton 1959 vol. 1, p. 187). It is thus quite likely that “force” is a physico-mathematical construct in the Principia and Newton’s interlocutors on the Continent seemed to perceive it this way. Far more disconcerting, the concept of attraction, wherever it rst occurred in the Principia, did not t Huygens’ “neoCartesian” rationalism. In addition, the Dutch scientist perceived the inuence of this non-rationalistic conception of attraction on Newton’s mathematics. He wrote: “I am not in agreement with a principle that he assumes in this calculation and elsewhere, which is that all the parts one could imagine in two or more different bodies mutually attract and tend to approach one another” (OCCH vol. 21, p. 471). The derivation of the shape of the earth, Huygens’ subject here, and the inverse square law, were connected to the underlying concept of attraction. Notice that Huygens was not the only one to perceive the close connection between the signicance of attraction and Newton’s mathematics. Bernard le Bovier de Fontenelle (1734, p. 217) also pointed out that the proportionality of weight to mass and the reciprocity of action indicate that attraction is obscurely inherent in bodies. Attraction was not a neutral concept vis-à-vis Newton’s calculations. As a central concept that he required in constructing physical theory, it placed the Principia beyond the bounds of acceptable science according to Cartesian standards and values. Huygens consequently disapproved of Newton’s theory while recognizing that he himself had to pay a price for what Koyré (1968, pp. 158… 9) has called “his loyalty to extreme Cartesian rationalism.” As Koyré reminds us, having dismissed attraction to the outer boundaries of science, Huygens lacked a concept that allowed him 1) to convert centrifugal force to centripetal force, 2) to demonstrate the elliptical form of the planetary orbits, and 3) to generalize the effect of weight. Despite this wonderful explanatory power, Huygens denied that the concept was fruitful for physics because it violated his criteria of sound achievement in mechanics. He maintained that attraction, clinamen, and levitas all reected the same kind of error from which Descartes had wisely saved physics. The rise of modern science was due to a break with these conceptual traditions. In this way, Newton’s philosophy of science contrasts sharply with Huygens’: for example, prior to attributing his law of inertia to Galileo in the Principia, in a fragmentary draft connected to his book, Newton had already attributed it to Ancients such as Lucretius, Perspectives on Science 149 Aristotle, and Anaxagoras.22 In brief, while tradition might be for Newton a good criterion for theory appraisal, for Huygens it was an obstacle to the development of science. I will tentatively call these two philosophical attitudes respectively “backward looking” epistemology and “forward looking” epistemology.23 Thus making a distinction between mathematical demonstration and physical account in the Principia would not necessarily have had an impact on the debate. In point of fact, Huygens may have had empirical and theoretical reasons to reject Newton’s theory. In addition, he simply did not seem to believe that mathematical description could exhaust physical science. For Huygens, Newton made beautiful mathematical discoveries but failed to complete the scientic revolution begun by people like Descartes. These kinds of criticisms, which were fairly common on the Continent, prompted what I called the eclipse of Newton’s theory of general gravitation in key Continental scientic institutions. But they also showed Continental revolutionaries how the Principia needed to be redirected. In particular, the conceptual mismatch between the theory of attraction and the new philosophy of nature, deeply entrenched on the Continent, seems to have engendered in “Newtonians” of the Paris and Basel mathematical schools a kind of cognitive dissonance. A slow process of revision began, resulting in the triple dissociation mentioned earlier. 3. Th e analytic redirection of the Principia In the seventeenth century, as A. Rupert Hall (1975 vol. 13, pp. 233… 4) reminds us, the French and the English were rivals. They alone had well organized and well nanced scientic institutions. French and English journals were current sources for other editors. When Newton’s Principia appeared at the close of the century, Cartesian physics had already shaped science in France. For example, Rohault’s Traité de physique, published in 1671 was in its fourth edition in 1682 and in its twelfth in 1708. Also, Fontenelle’s Entretiens sur la pluralité des mondes in 1686 and Regis’ Système de philosophie in 1690 aimed at beeng up the Cartesian system. Thus, the two Royal Academies differed greatly in their way of perceiving and describing physical objects. This difference seems to have determined the scientic style of the rst great French mathematical proponent of Newton’s theory, Pierre Varignon. As Voltaire (1988, pp. 70… 1) wrote, things changed so critically between the English and the French after the publication of the Principia that there was no way to come to an agreement even on the denition of 22. See I. Newton, MS. Add. 3970, fol.652a. 23. See below for more details. 150 The Reception of Newton’s Gravitational Theory mind or matter. 24 However, the mathematical accomplishment of the Principia was attractive even to such great opponents of Newton’s as Leibniz, an inuential and respected authority in France. Even though Leibniz opposed the physical account of the world in Newton’s book, he praised Newton for having made an “astonishing discovery” about Kepler’s laws and encouraged him to persevere in handling nature mathematically.25 In the same vein, he encouraged the young French mathematician Varignon to pursue the process of mathematizing nature.26 Varignon was also cognizant of the genius of the Principia, and his writings already referred to it in the 1690’s. By then, French scholars vehemently rejected Newton’s theory of attraction, much as did Huygens and Leibniz. Varignon, however, was aware of the conservative motivations involved in such a scientic debate, as he had himself to ght against those whom he called the old style mathematicians in order to save the new Leibnizian methods.27 In this atmosphere of vigorous controversy, Varignon successfully paved a new way for Newton’s theory without making any outstanding discovery: that was the path of mathematical analysis. He seemed to turn the Leibnizian project of connecting mechanics and the differential calculus 28 into a new program of research, that of applying the new analytic methods to Newton’s Principia. Varignon’s achievement was the rst signicant step in the methodological redirection of the Principia. 24. Voltaire’s eloquent description seems to have anticipated the idea of incommensurability between two theories. 25. In his letter to Newton, already partially quoted, Leibniz encouraged Newton to “continue to handle nature in mathematical terms . . .” He then added: “You have made the astonishing discovery that Kepler’s Ellipses result simply from the conception of attraction or gravitation and passage in a planet. And yet I would incline to believe that all these are caused or regulated by the motion of a uid medium, on the analogy of gravity and magnetism as we know it here. Yet this solution would not at all detract from the value and truth of your discovery . . .” (Newton 1961 vol. 3, p. 258). 26. Notice that Varignon’s Projet d’une nouvelle méchanique, appeared in the same year as the Principia. By means of the parallelogram of forces, Varignon also dealt with some problems that the Principia ignored. Similarly, his Nouvelles conjectures sur la pesanteur appeared in the same year as Huygens’ Discours sur la cause de la pesanteur. 27. See Varignon’s letter to Johann Bernoulli on August 6, 1697 (Bernoulli 1955… 92 vol. 2, p. 124). In 1700… 1701, Varignon refuted Michel Rolle’s contention that the new calculus was not coherent and that it was misleading. 28. For example, Leibniz published two papers in 1689 in the Acta eruditorium (Schediasma de resistentia medii & motu projectorum gravium in medio resistente and then his Tentamen de motuum coelestium causis), where he systematically attempted to solve mechanical problems with his new methods. Leibniz claimed that he wrote the Tentamen before reading the Principia. But recent studies seem to indicate that this may not be the case (Bertoloni Meli 1988, 1991, 1993). Perspectives on Science 151 It must be noticed above all that it was not only the adversaries of the Principia who tried to select out its mathematical aspects. In England, Newton’s followers such as John Keill and Richard Bentley, to name but few, saw a weapon against atheism in the theory of gravitation. Nevertheless, Keill (1698) argued that one should exploit the mathematical aspect of Newton’s work rather than its cosmological dimension.29 But the crucial fact was that the English mathematical movement remained in conformity with Newtonian symbolism and methods (Guicciardini 1989).30 It is only during the second half of the eighteenth century, as Guicciardini (1999, p. 193) reminds us, that “British authors” became “convinced that slavish adherence to the Principia’s geometrical methods would ultimately lead to total sterility.”31 In striking contrast to the English intellectual universe, Varignon initiated an entirely new path about a half century earlier. It consisted in transposing the most important propositions of the Principia into Leibnizian symbolism. Indeed, at the turn of the eighteenth century, Varignon (1700a, b, c, 1710, 1725; Peiffer 1990) began to use the differential calculus to treat certain problems of the Principia in the context of developing the general theory of central forces. This kind of connection between Newton’s mechanics and Leibniz’ methods, that is to say, between the geometrico-innitesimal and the differential approach, was an important step towards analytic mechanics. It is now generally accepted that Newton and Leibniz independently discovered analytic methods.32 However, for Leibniz, who searched for a characteristica universalis, the differential calculus is superior to previous mathematical methods and is nothing less than an ars inveniendi, an art of invention or a method of discovery that can operate by cogitatio caeca or blind reasoning. For Newton, who hoped to retrieve a prisca sapientia and geometria, analysis may help discover scientic truths but the synthetic method of uxions presents the advantage of allowing a visualization of such truths. He accordingly chose a geometrical representation of force in the Principia. Historical records and recent studies indicate that Newton 29. But Keill (1758) himself tried, with some indelity to Newton, to derive Newton’s laws of motion from experiment. He presented innite divisibility purely and simply as an indemonstrable postulate. Further, for some scholars, the Principia offered a model of scientic approach to be transferred to almost all the domains of knowledge (see for example the Principia medicinae theoreticae mathematica of Cheyne, the Mathematical Elements of Natural Philosophy conrmed by Experiments . . . of ‘sGravesande). 30. On British natural philosophy versus mathematics see Schoeld (1970). 31. Indeed, the attempts to connect the Principia and the analytic methods by people like Cotes, Gregory, and Keill were limited. 32. For more details on the subject of this paragraph see Guicciardini (1999) and De Gandt (1995). 152 The Reception of Newton’s Gravitational Theory was perfectly able to provide an extensive analytic account of force in his masterpiece but at least partly because of the particular philosophy of science he adhered to, i.e., the backward looking epistemology, he increasingly became convinced of the superiority of geometrical approaches over analytical ones (Guicciardini 1999, pp. 17… 38, 99… 117). Indeed, the backward looking epistemology posits that the intellectual achievements of the Ancients (such as the Egyptians, Phoenicians, Chaldeans, and the Greeks) hide scientic methods and truths about nature that are if not superior at least equivalent to those of the Moderns (Casini 1984).33 From a methodological point of view, Newton sought to align himself with the Ancients who, he claimed, discovered their theories analytically but presented them geometrically (Newton 1967… 81 vol. 8, pp. 453… 5). It is interesting that d’Alembert ([1805] 1965 vol. 2, p. 320; 1770 vol. 4, p. 176) and Laplace ([1884] 1878… 1912 vol. 6, p. 464), just as Euler (1736), were already cognizant of this methodological difference when they pointed out the importance of the geometry of the Ancients in Newton’s public work. In brief, where Leibniz wanted to promote blind mathematical reasoning, Newton praised intuition and visualization (Guicciardini 1999, pp. 136… 68; De Gandt 1995). Thus not only is a distinctive ontology imbedded in Newton’s theory but also a specic methodology driven by a particular philosophy of science. Newton’s backward looking epistemology contrasts with Varignon’s forward looking epistemology. Starting from gures like Descartes, Huygens, and Leibniz, the forward looking epistemology posits that the intellectual achievements of the Moderns surpass the accomplishments of the past and hence provide universal standpoints. For example, though Leibiniz claimed that the Moderns do not give enough credit to the Ancients on specic matters such as mechanistic philosophy,34 he never 33. See my article “Newton Science and Alchemy: Half a Century of Controversy,” in progress. 34. Notice for example that Leibniz wrote his Discourse on Metaphysics in 1686, the same year Newton wrote De mundi systemate. In the Discourse, Leibniz made a move back to the scholastics to reintroduce substantial forms into modern philosophy. He even went so far as to contend that if their achievements were examined and claried by an open-minded person according to the methods of analytic geometry they might yield a great treasure of demonstrative truths. Newton all along has been convinced of something similar and in the De mundi systemate, as in other several writings, argued that scientic theories such as the heliocentric one were already known by the Ancients and are hidden in their works. It’s as if Newton were the open-minded analytic geometer Leibniz hoped for. What Leibniz could not, however, accept was attraction. We can say, based for example on the Tentamen, the Monadology, and the letters to Clarke, that, according to Leibniz, Newton went to the other extreme in the rehabilitation of the Ancients: bodies, though not reducible to pure extension, act on each other only through actual contact. Perspectives on Science 153 doubted, unlike Newton, the superiority of the differential calculus over previous mathematical methods. Likewise, Varignon, as we have seen, sharply drew the line between the mathematicians of the “old” school who deprecate the new analytic methods and those of the Leibnizian school who promote it. The whole controversy, he suggested, is due to the fact that Leibnizian methods allow young mathematicians to surpass mathematicians of the old style. He complained about the behavior of “mathematicians of the old style worried to see young mathematicians become their equals and even surpass them thanks to the calculus” (Bernoulli 1955… 92 vol. 2, p. 124). Thus, as early as 1697, Varignon already realized that the differential calculus opens progressive scientic avenues, and a few years later he undertook extensive translation of the Principia from its original geometrical style into the more progressive analytic methods. Varignon’s achievement inuenced not only the second edition of the Principia by Cotes in 1713, but equally the Phoronomia of Jakob Hermann, which constituted the “mathematical mother’s milk” of Euler until 1727 (Fellmann 1988). Moreover, thanks to their use of analytical and differential instruments, the annotated edition of the Principia by Thomas LeSeur and François Jacquier, from 1739 to 1742, inuenced d’Alembert decisively. How original was Varignon’s achievement? Later writers such as Charles Bossut, Jean Etienne Montucla, and Pierre Duhem were skeptical on the subject. They perceived Varignon as simply developing methods discovered by others (Duhem 1991 vol. 1, pp. 420… 1). For example, Varignon’s work on the inverse problem was just a bit more than a synthesis of Johann Bernoulli’s and Herman’s ndings. However, Lagrange (1788), for one, had already pointed out that Varignon had a share in the development of both the principle of the composition of forces and the basic axiom of statics, the principle of virtual work. D’Alembert extended the latter to dynamics. This enabled Lagrange to specify the class of problems which can be solved by the more systematic method of identifying a so-called Action integral which, when minimized, leads to Lagrange’s equations of motion. Recently, scholars have tended to emphasize Varignon’s contribution to the rise of analytic mechanics. His originality, as Michel Blay (1992, pp. 153… 221) noted, consisted in this: by formalizing the problems of geometry systematically by means of Leibnizian methods, he traced a new trajectory for the science of motion. In Comtian terms, he reduced mechanical problems to simple analytical procedures, that is to say, to simple calculations by differentiation or by integration. In contrast to Leibniz and Newton, Blay observed, Varignon achieved this result by the construction of a notion of velocity and of accelerating force at each instant. 154 The Reception of Newton’s Gravitational Theory Varignon was not the only one to connect Newton to Leibniz. Johann Bernoulli and Guillaume de l’Hospital did much the same (Aiton 1986, 1989). Varignon was one of the very rst Frenchmen to begin using the new Leibnizian methods, thanks to Johann Bernoulli (Fleckenstein 1945; Robinet 1960; Costabel 1976). Moreover, works of such distinguished “Newtonians” as Euler, though following Varignon’s path, clearly show a strong inuence of Johann Bernoulli. However, Bernoulli and de l’Hospital did not seem to have perceived, as Varignon did, that there was a great deal at stake in systematically basing Newton’s physics on this new instrument. Varignon had transformed the casual connection of Newton’s theory to Leibnizian methods into a systematic enterprise that seemed to orient physics in a more self-sufcient or “agnostic” way. Varignon contributed to the rise of a new conception of mechanics as simply a domain of analysis. A new scientic style began to emerge. Later, physics was conceived as a purely logical deduction starting from a general algorithmic expression, which liberated mathematics from the realistic intuition that was crucial for Newton. The formalization of the central aspects of the Principia by means of the differential calculus constituted a rst reworking of Newton’s achievement and the starting point of the methodological dissociation from Newton by the Continental revolutionaries. Initially, mechanics implied a theoretical description of physical objects. The successes of this reworking and methodological dissociation produced a new perspective on the interpretation of Newton’s theory. The analytic redirection began somehow to mask the ontology of force, the target of Huygens and Leibniz. Varignon’s version of “Newtonianism,” which found its most complete fulllment some decades later, systematically reduced the questions of physics to the art of solving equations. It is this appropriation of Newton to a Leibnizian mode of thought that brought about what Francois De Gandt (1995, pp. 271… 2) called a “neutralization of the study of force.” The methodology of the Principia can be described from different perspectives yet not necessarily mutually exclusive thanks to the extreme rigor and extraordinary creativity displayed by Newton in the course of the geometrical translation of force. For example, Cohen (1980), as we have seen, described it as a “mathematical construct.” George Smith (2002a, pp. 142… 3) characterized it from logical point of view as an “if-then” logical approach contrasting it with Galileo’s and Huygens’ approaches that he identied as a “when-then” form of reasoning. In fact, Newton’s mathematical and logical ability allowed him to subject force to a quantitative treatment. The backbone of this treatment is the “rst and ultimate ratios” for which he actually provided a geometric as well as analytic version. Cohen’s and Smith’s descriptions provide useful explanations Perspectives on Science 155 of how Newton became methodologically capable of postponing a physical account of force. However, being able methodologically to postpone this task is different from masking the problematic ontology of force or stripping the geometrical “translate” of force from any ontology. Apparently, Newton’s theory conjoined geometry and ontological assumptions in such a way that it took the analytic move of Varignon to help progressively “desensitize” its reception on the Continent. Otherwise put, the fact that Newton didn’t ll the Principia with descriptions of alchemical processes and theological designs to account for gravity but successfully subjected force to a geometrical treatment was a great revolutionary step. But to analytically map motion in a way that progressively “neutralizes” the ontological underpinnings of the notion of force is another step towards a revolution. I maintain that this analytic mapping of motion that began with Varignon created a methodological distance between Newton and the Continental revolutionaries. It led to the emergence in the mid-eighteenth century of new exemplars of solving problems that Curtis Wilson called “a newer new analysis” (Wilson 1995, 2002). Varignon’s great discretion in the controversy between Newtonians and Cartesians, while matched by a resolute exploitation of the mathematical aspects of Newton’s work, appear to inaugurate a new attitude in the reception of Newton’s theory and consequently in the practice of physics as such.35 This attitude encouraged exibility with respect to theoretical problems. And for good reason: As d’Alembert (1967 vol. 1, p. 74) wrote, young mathematicians from all over Europe solved the conict between Cartesianism and Newtonianism. It was in mathematics that a new relation to the Principia began to take shape. As a result, a new image and a new style of scientic practice emerged. Varignon thus seemed to initiate not only a new style, but also new ideals and standards different from Newton’s. Though he did not convince the French Academicians to accept Newton’s theory, he helped resuscitate the Principia from its eclipse as a valuable achievement in physics. However, to save the theory of general gravitation on the Continent denitively, a kind of holistic defense of the Principia was needed. 35. Similarly, Varignon avoided taking sides in the conict between Leibniz and Newton over the calculus. Varignon became close to Newton from 1713 on and, in 1714, he was elected to the Royal Society. Newton had already been elected Foreign Member of the French Academy in 1699. Varignon played an important role in the reception of Newton’s Opticks in France. This reception was easier than the reception of the Principia thanks to Malebranche and his followers. Guerlac (1981) argued that the attitude of the so-called Malebranchist group weakened the Cartesians’ position in the debate over the Principia. 156 The Reception of Newton’s Gravitational Theory 4. Maupertuis’ mechan istic reinterp retation of the Principia Two strategies characterized the controversy about Newton’s theory in the French Academy. One can be called the lter solution, the other intratheoretic perseverance. The lter solution consisted in interpreting the spirit and the fundamental concepts of a theory by use of an alien ontology. As a result, the signicance of both Newton’s and Descartes’ concepts was radically modied. Intra-theoretic perseverance was the attitude that consisted in claiming that one still supports the same theory one is radically reinterpreting 36. By using these strategies in the context of the debates over Newton’s Principia, Maupertuis seemed to suggest that the theory of attraction was a perfect completion of the mechanistic science that Descartes sought, but failed to achieve. Thus, according to Maupertuis, Newton’s science displays the true structure of mechanism. I will call this paradoxical union between two rival theories a theoretical two-in-one. During the eclipse and under the direct inuence of Huygens and Leibniz, Cartesians perceived attraction as “absurd” or “occult” or as a “return of chimeras.” They blamed Newton vehemently for violating the mechanistic framework and scientic standards of the new philosophy of nature. Varignon limited his defense of Newton’s theory to an analytical strengthening of the Principia. For Maupertuis, however, things had changed and the time had come to furnish another reading of the Principia. He was quite aware that he was distancing himself from Newton. He presented his main thesis in 1732 as a simple hypothesis. After the success of his Discours sur les différentes gures des astres, he wrote modestly that he was himself very cautious about his own conjectures about attraction, and, that if he “decided to go some steps further than Newton, it was not without awe and hesitation” (Maupertuis [1756] 1974 vol. 2, p. 287). How did he differ from Newton? In 1732, Maupertuis proclaimed that Newton believed that attraction could be a result of some subtle matter produced by material bodies, and that it could really be an effect of impulse (Maupertuis [1732] 1974 vol. 1, p. 92). Clearly, this would allow attraction to be understood almost in the same manner as Cartesian vortices. Maupertuis, however, inquired in his Discours whether a reasonable understanding of the Principia (Maupertuis 1974 vol. 1, p. 94) could be achieved by linking attraction directly to material bodies. He declared that attraction is not a mysterious reality but just an empirical principle, 36. Notice that such Cartesians as Malebranche, Louville, Dortous de Mairan, and Johann Bernoulli also used the same strategies. For example, Bernoulli’s reinterpretation of Descartes’ vortices borrowed from Newton’s theory. Perspectives on Science 157 or, more exactly, “a rst fact” that must be validated in nature (Maupertuis 1974 vol. 1, p. 92). How to justify this natural character of attraction? Maupertuis adopted a triple strategy. After offering an account of the physical data involved in the debate, he combined 1) a metaphysical discussion and a philosophical evaluation with 2) the principle of the black box in view of 3) redening the objective and the goal of science. If attraction is a simple, natural, empirical principle, it must necessarily be linked to matter. But then it must not be metaphysically impossible. Maupertuis stressed that attraction did not imply any metaphysical impossibility or even a logical contradiction. For Cartesians, attraction was, metaphysically speaking, a monster. It implied action at a distance and could not be explained by the received mechanistic philosophy. To refute this view, Maupertuis’ rst step was to reply that there is no relevant conceptual barrier for conceiving attraction as a material property. In fact, if attraction cannot be linked to matter as Newton maintained, then it must be hidden somewhere in an unknowable space as an unknowable entity. As such, it would be a real metaphysical monster at least viewed from the Cartesian perspective. Once Maupertuis brought attraction entirely back into the material universe, the only question that remained to be solved was how, as a material property, it was related to material things. Maupertuis’ second step was to enlarge Locke’s agnostic perspective. He argued that we are not only ignorant of the essence of things, as Locke taught, but also that we do not have exhaustive knowledge of their material properties or of the way in which properties reside in bodies. Our knowledge of bodies in general is strongly limited (Maupertuis 1974 vol. 1, pp. 94… 8). Here in fact Maupertuis was breaking through the barriers set by Huygens; he sharply undermined Cartesian philosophy on two points. First he contended that, in addition to its geometrical properties, matter may have many other properties, however unknown to us. To reinforce this argument he elaborated on both Locke and Malebranche (Hankins 1967)37 in establishing a philosophical equivalence between attraction and impulse. Neither the one nor the other is directly intelligible to us (Maupertuis 1974 vol. 1, pp. 98… 103). Second, in consequence, he argued 37. Newton himself seemed already to have created a climate of ambiguity around the notion of impulse, by using it now and then strategically, as if it had the same status as attraction. And Locke had clearly called its intelligibility in doubt in his Essay. Similarly, for Malebranche in his Search after Truth, impact was only an occasion for the expression of the real cause of impulse, which is the will of God. Consequently, Maupertuis concluded, impulse is not intelligible to us unless we lose the habit of asking ourselves about it because of its familiarity. 158 The Reception of Newton’s Gravitational Theory that the appraisal of scientic theory could no longer be a theoretical affair but must be an empirical enterprise. His point seems to be that if attraction is neither metaphysically impossible nor logically self-contradictory and if, further, our knowledge of physical properties is limited, we must inquire by experimental means only whether attraction has an effective place in Nature: “Attraction is nothing else, so to speak, but a question of fact; it is in the system of the Universe that we must inquire whether it is a principle that, effectively, has a place in Nature, up to what point it is necessary in order to explain the phenomena, or, nally, if it is introduced uselessly to explain facts that can be explained without it” (Maupertuis 1974 vol. 1, pp. 103… 4). Maupertuis’ results are threefold: he lifted the metaphysical interdiction of the Cartesians; he easily burst through the Cartesian-Huygenian impasse by his enlargement of the agnostic perspective; and he showed that settling the question about attraction required empirical testing but not a theoretical dispute. This means that scientists can reject attraction only if they have proved by experiment that it doesn’t occur. In terms of consequences, if attraction is only a question of fact, we can apparently tuck away in a black box the question of the cause of which it is the effect, leaving it, Maupertuis asserted, to more “sublime Philosophers” who are capable of lifting themselves towards “the wisdom of the Sovereign Intelligence” (Maupertuis 1974 vol. 1, p. 93). On this reading then, the sole task we should reserve for science is to deduce the explanation of natural phenomena from a rst empirical principle. What Maupertuis seemed to argue here was that the debate over attraction no longer had a place within science. The dispute was philosophical and should be cut off from scientic practice. Empirical testing should be the unique criterion of scientic undertaking. Actually, Maupertuis’ strategies led him to a very special shift in the theoretical framework. He reinterpreted the concept of attraction so that it became congruent with mechanistic semantics. It signied henceforth a physical effect resulting from the mechanistic nature of bodies, having the same ontological status as impulse, compared to which it nevertheless had superior explanatory power. Here lies Maupertuis’ originality: in ltering the concept of attraction to t into mechanistic contexts, he elaborated a kind of two-in-one that could bring mechanical philosophers and Newtonians into the same camp. This quasi-mechanistic status that Maupertuis (1974 vol. 1:pp. 132… 3, 136, 138, 140… 1) elaborated for attraction produced an empiricist philosophy of science according to which scientic practice would consist in verifying whether a proposed theory is empirically valid or whether it is excess baggage. This means that science Perspectives on Science 159 could then dispense with a clear philosophical description of its fundamental concepts as long as experiment validated them.38 Maupertuis was not alone: Newton himself had already claimed that his theory of attraction was experimentally based. However, he did not convince his peers on the Continent because of the ambiguous status of attraction in his theory. ‘sGravesande, who inuenced French “Newtonians,” also found in Newton’s work a framework for the development of experimental physics and a defense of empiricism. But Maupertuis differed from them in building a systematic mechanistic revision of Newton’s framework. This very mechanistic and empirical reduction explicitly allowed modication not only of the goals of science, but also of the relations between philosophy and science. Like the other Continental revolutionaries, Maupertuis undertook here an ontological and philosophical dissociation from Newton. Maupertuis’ mechanistic and empiricist framework might have inuenced Clairaut in 1747 during the lunar apogee crisis. Referring to Buffon’s metaphysical argument, Clairaut declared that nonmathematical argument had no weight in the debate over Newton’s theory (Euler, 1911… 86 vol. 4, p. 186).39 At the same time, Maupertuis’ conceptual inversion of the meaning of attraction seems to have profoundly changed the reading of the Principia. His pupil, Voltaire ([1734] 1988, p. 86), attributed to Newton the idea that “there is a central force in all bodies” which acts from one end of the universe to the other, on the nearest and the farthest bodies, according to the immutable laws of mechanics. Following Maupertuis, he added that we should keep in mind that we could not know the cause either of impulse or of attraction, which is also a “property of matter” (Voltaire [1738] 1992, p. 344). A scholar today can legitimately wonder to what extent these reinterpretations of the Principia were mechanistic. However, it must be remembered that the “Newtonians” were themselves aware of their mechanistic outlook. In addition, such “Cartesians” as Johann Bernoulli and Fontenelle clearly recognized the mechanizing process to which the Principia had been subjected by the “Newtonians”. Bernoulli strongly disapproved of the change in meaning that the “Newtonians” tried to effect in the conceptual framework of the Principia. He urged the partisans of Newton to follow the example of their master instead of claiming that the 38. However, Maupertuis did not forbid himself to meddle with metaphysics and although his principle of least action seemed to rest on the foundation of an empiricist philosophy, Maupertuis read in it a proof of the existence of God (De Gandt 1999). 39. About the conict over the role of mathematics in physics see Gingras (2001). 160 The Reception of Newton’s Gravitational Theory void and attraction were realities in the nature of things and that they were principles of existence (Bernoulli 1735 1:265). In a word, Bernoulli was chastising his fellow Continental revolutionaries for their ontological dissociation with Newton. Indeed, as Fontenelle noticed, the semantic changes undertaken by the “Newtonian” Continental revolutionaries led them towards a change in the theoretical framework of the Principia. He seems to have been particularly shocked by the process of redirecting Newton’s theory. He exclaimed: “Behold attraction, which shows itself here unveiled; for all the tendencies of bodies towards central points can always be reduced to mechanical ideas, or at least it would not seem to be impossible that they should be; but as soon as a body acts by its mass on another distant body, we cannot conceal the fact that this is attraction in the strict sense of the term” (Fontenelle 1732, pp. 132… 3). That is precisely what the “Newtonian” Continental revolutionaries aimed at through their mechanizing lter, changing the descriptive and ontological perspective of the gravitational theory. Unlike Bentley and Cotes, for example, Maupertuis made attraction undergo a real slippage in meaning by a systematic ontological and philosophical revision of Newton’s Principia. He created a conceptual gap between his theory and Newton’s. Maupertuis seemed to have realized that the only way to save the Principia on the Continent was to reorient the understanding of its central concepts in mechanistic style. For Maupertuis, curiously, the reading of the Principia that Newton had sharply disapproved of was the only one that t this purpose. Maupertuis linked attraction directly to material bodies though Newton had written: “That Gravity should be innate, inherent and essential to Matter, so that one Body may act upon another at a distance thro’ a Vacuum, without the Mediation of any thing else, by and through which their Action and Force may be conveyed from one to another, is to me so great an Absurdity, that I believe no Man who has in philosophical Matters a competent Faculty of thinking, can ever fall into it.”40 Maupertuis might not be a talented philosopher in Newton’s sense, but he did demonstrate outstanding philosophical ability. In fact, if attraction could be conceived as a property of matter, if the agnostic perspective about our knowledge of material body could be enlarged, and if a theory of attraction could be supported by strong experimental proofs, then there would be sound reasons to interpret the Principia as exemplifying an em40. Newton was writing to Bentley on February 25, 1693. However, the fact that Maupertuis may not be aware of this particular claim from Newton is irrelevant to the discussion. Perspectives on Science 161 pirically based mechanistic philosophy. In an extraordinary tour de force, Maupertuis praised Newton’s theory as the true mechanism, in contrast to Cartesian mechanism, which would henceforth exhibit only an appearance of mechanism. He wrote: “[The Cartesians] were so delighted to have introduced an appearance of mechanism in their explanation of Nature that they rejected the true mechanism without any analysis” (Maupertuis [1756] 1974 vol. 2, p. 284). For Maupertuis, the mere use of the concept of attraction did not separate mechanistic from non-mechanistic achievements. The demarcation between mechanism and non-mechanism was provided by the empirical reasons used to advance a theory. Accordingly, he dismissed the use of the concept by some French savants, particularly Fermat, as non-mechanistic, because those people, he said, had no critical distance vis-à-vis the concept. Moreover, unlike Newton, they did not have any good evidence in support of their theories (Maupertuis [1732] 1974 vol. 1, pp. 138… 40). As far as gravitational theory is empirically proven, we may admit that Newton conceived attraction mechanistically. To appreciate the subtlety of Maupertuis’ argument it will help to contrast it with that of Cartesians such as Fontenelle. Fontenelle (1968 vol. 1, p. 611) argued that Newton’s theory, though remarkably supported by experiment, was nonetheless false as a physical theory. Newton’s theory was false because it did not rest on coherent mechanistic bases. Accordingly, Newton’s contribution to science lay solely in geometry, while Descartes was the real instigator of a sound physical achievement even though the Cartesian theory was not supported by experiment. It was this logic of theory appraisal that Maupertuis changed. For him, a truly mechanistic theory ought to be experimentally based; if Newton’s and Descartes’ theories were truly mechanistic theories, they both had to be proved by experiment. Only Newton’s theory was proved by experiment, therefore, only Newton’s was a truly mechanistic theory. Otherwise put, since a theory of attraction is supported by experiment, the theory of attraction that is proven by experiment is a truly mechanistic theory. Logically, the relevant scientic issue about attraction is then experimental. Armed with this theoretical revision, Maupertuis launched into a vigorous onslaught against the French Academy while using derision to humiliate his opponents.41 41. To be sure, reason is a motif with limited force, and, as La Baumelle emphasizes, “attraction no longer pleases young academicians who did not have their own prejudices to combat,” but was detested by all those who “renounced only with pain the opinions of their youth.” On the non-scientic methods used by Maupertuis, see La Baumelle (1856, pp. 31… 4). Maupertuis, who, according to d’Alembert, was the rst to believe “that one could be a good citizen without blindly adopting the physics of one’s country,” 162 The Reception of Newton’s Gravitational Theory Clearly, on current understanding, Maupertuis’ theoretical two-in-one, through which Newton and Descartes were ultimately embedded in the same theory, is incommensurable vis-à-vis Newton’s views in the Principia. However, at the same time it undermines the concept of incommensurability on one point: scientic theories are ontologically permeable and inter-penetrable. Indeed, Continental revolutionaries were so successful in changing Newton’s ontological and philosophical framework in the light of the competing mechanistic theory that the habit arose of reading the Principia as a purely mechanistic accomplishment comparable to that of Descartes or Boyle. In the last two centuries, historians have maintained that Newton had puried the concept of attraction as far as possible of its occult signication and that he had always followed Boyle’s mechanistic style (Hall 1958, pp. 243… 4). During the period of eclipse, it is clear that Newton was not understood in this way. For Leibniz (1965, p. 417), the Principia constituted the breaking point with the key tenets of such mechanical philosophers as Boyle. The possibility of interpreting Newton in a mechanistic way was a major accomplishment, forged by Continental revolutionaries, and this interpretation was not possible until after the transformation wrought by Maupertuis and, later, by d’Alembert and Euler. Maupertuis’ point was that, though the concept of attraction could rightly be described as non-mechanistic in certain cases, Newton had constructed it in a highly mechanistic way in the Principia. Thus, far from being an opponent of mechanism as it was constructed on the Continent, Newton brought mechanistic science to completion. In this way, Maupertuis seems to have established the basis for a modern reading of the Principia. Later on Voltaire and Madame du Châtelet joined him in the ght against what more and more appeared to be French ideological resistance to Newton. The eclipse was over and Newton’s theory could be developed with great exibility in a kind of mechanistic framework. An intensive period of technical revision started on the Continent, mainly with Euler, d’Alembert and Clairaut. Maupertuis (1974 vol. 2, p. 286), later, referred to the works of these three people as showing how Newton’s theory was nally successful on the Continent. Conc lusion I have been arguing that when the Principia was published in 1687 Newton’s theory of general gravitation underwent an eclipse in key Conti(D’Alembert 1967, p. 73) was fully aware of the ideological motivations of the debate. At about the time of publication of Maupertuis’ Discours, the writings of such Cartesians as Dortous de Mairan (1733) and Joseph Privat de Molières (1734… 9) became more favorable to Newton. Perspectives on Science 163 nental scientic institutions. It took Varignon’s analytic redirection and Maupertuis’ mechanistic reinterpretation of the theory to help resuscitate it. Through various strategies, Continental scientists reformulated the theory, dissociating themselves ontologically, methodologically, and philosophically from Newton. I maintain that the result of this revisionary enterprise is better understood in a theoretical framework that reconciles Kuhn’s notion of invisible revolution and Whewell’s ascription of the completion of dynamical studies to the post Newtonian period. At the institutional level, despite the undeniable contribution of the British school, the major agents in this reworking of Newton’s theory towards what can be characterized as a synthetic theory of attraction were the Basel and Paris’ mathematical schools. These two institutions were shaped in the main by a combination of German (Leibiniz), Dutch (Huygens), French (Descartes), and, of course, English (Newton) inuences. 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