SOURCE: "Voltaire and the Enlightenment Image of Newton," in History & Imagination: Essays in Honor of H. R. Trevor-Roper, Hugh Lloyd-Jones, Valerie Pearl, Blair Worden, eds., Holmes and Meier Publishers, 1981, pp. 218-32.

[In the following essay, Rattansi analyzes Voltaire's interest in Newton and his scientific writings, tracing the impact Voltaire had on the public's acceptance of Newton's conception of the universe, as opposed to that of René Descartes.]

While the publication of the Principia Mathematica in 1687 secured almost universal admiration for the scientific and mathematical genius of Sir Isaac Newton, his contemporaries differed widely in their assessments of what he had achieved in his masterpiece. Edmond Halley placed Newton's genius nearest to the gods in the ode he prefixed to that work. One of Newton's greatest scientific contemporaries, Christian Huygens, was astonished, however, that Newton should have chosen to rear his magnificent structure or such a 'manifest absurdity' as the idea of an universal attraction.' Leibniz was to accuse Newton of having turned all the operations of nature into a perpetual miracle.² Brought up on Cartesian rationalism, Huygens and Leibniz saw in the acceptance of 'unintelligible' attraction a reversion to the 'occult' qualities of the despised scholastics and an abandonment of that luminous clarity the Cartesian revolution had brought into physical thought. It was the combination of 'rational' (a rigorous mathematical-mechanical method) and 'irrational' (the use of a notion of force not reducible to mechanical impact) that they found dismaying and disconcerting in Newton. The first review of the Principia in the Journal des Savants set the tone for the dominant continental response. The reviewer recognised that Newton had laid claim to the creation of a new 'system of the world'. What he had created, in fact, was a system of mechanics, more perfect than anyone could have dared to imagine, but based on assumptions that were arbitrary and unprovable. Newton wrote as a geometer, not as a physicist. Only when he substituted true motions in place of the ones he had imagined would he succeed in founding a new physics.³

Nearly half a century was to pass before Newton found worthy champions in the land of Descartes. Recalling that time, the physicist Maupertuis wrote of the timidity, fear and caution with which, in his earliest work of 1732, he had pleaded with his countrymen not to dismiss Newton's concept of 'attraction'-out of hand. According to Maupertuis, the notion remained almost wholly confined to its island home. If it ever chanced to cross the Channel, it was feared as a monstrous apparition. So charmed were those on the Continent with having given a semblance of the mechanical to their explanations of nature, 'that they rejected without hearing true mechanism when it offered itself.⁴ But Maupertuis was not alone. He was soon joined by a populariser of genius, Voltaire. Once he had been reassured by Maupertuis of the scientific worth of Newton's work, Voltaire used all his propagandist skills to familiarise an educated public with Newton's ideas and to persuade it to adopt them. He succeeded in achieving Newton's apotheosis as the founding father of a new age of reason.

Long familiarity has dulled the surprise we ought to feel at Voltaire's taking it upon himself to dethrone Descartes and install Newton as a pioneer of the Enlightenment. To have made the Cartesian mode of explaining nature appear no more than 'a semblance of mechanism', while conferring the status of la mechanisme veritable on a system based on attraction, was no mean achievement. Why did that cause enlist Voltaire's passionate interest and how did he help to carry it to victory? Those questions deserve a serious answer since it is Descartes who, at first glance, would seem to be a much more fitting symbol for an age of reason.

Descartes had supplied a philosophical basis for the ancient dream that the lucidity and rigour which seemed uniquely characteristic of mathematical reasoning could be extended to all human knowledge. Aristotle had traced the power of mathematical demonstration to the patterns of reasoning it employed. By formalising it in his logic, he believed he had laid the way open for the attainment of a comparable degree of certainty in other fields of knowledge. For Aristotle such an enterprise by no means demanded that the richness of the sensible world be reduced to the pale abstractions of mathematics, as Plato had attempted in his Timaeus. By the sixteenth century, the scholastic-Aristotelian edifice of knowledge aroused in some innovators the same revulsion as the Gothic cathedral. They reverted to the classical ideal of mathematical harmony as articulated by Pythagoreans and Platonists. That ideal inspired and provided the justification for Copernicus' overthrow of ancient cosmology and substitution of a more 'harmonious' system of the world. The appeal of his reform remained largely confined to those who, like Kepler and Galileo, accepted the mathematical ideal. It was Descartes who grasped that their piecemeal attempts to amend the old structure were futile.

In his Discourse (1637), Descartes had compared received knowledge to a ruined building, now beyond repair. It must be razed to the ground. A new one was to rise in its place, on new foundations and according to the design of a single architect, Descartes himself. It was to be a classical edifice, not the Gothic monstrosity with which his teachers had familiarised him at La Fleche. Mathematics was again to supply the supreme model for all human knowledge. By accepting that ideal, Descartes was rejecting Aristotle's view of the power and fascination of mathematics.

For Aristotle the conviction carried by mathematical demonstration lay in the patterns of reasoning it embodied, not in its use of such specifically mathematical concepts as points, lines, surfaces and solids. Each science had its own appropriate basic concepts and entities, and in each it was possible to arrive at secure knowledge by valid reasoning. The immobile and insensible served the science of the immobile and insensible, that is, of mathematics. It would be quite inappropriate to build up a science of the changing and the sensible realm of physics by using Plato's geometrical atoms. Aristotle's four elements, themselves sensible and changeable, could explain changes in that realm far more adequately.⁵

Descartes insisted that the power of mathematics resided in its indubitable starting-points. Nothing short of the certainty available in arithmetic and geometry was to be aimed at in all human knowledge. That could be attained only by confining attention to questions of order and measure. Our ideas would then carry the hallmarks of truth: clarity and distinctness. Sense experience was delusive and confused, and sensed qualities were utterly dependent on the more basic mathematical features of matter as it impinged on the senses. The simplest basic concepts for physics were matter and motion.

Voltaire did not deny Descartes' importance as a destroyer of old ideas. He had given sight to the blind.⁶ But he had expelled ancient reveries only to introduce novel chimeras.⁷ 'A man who disdained experience, never cited Galileo, and ventured to construct without materials, could not but erect an imaginary edifice.'⁸ Descartes' system had turned for Voltaire into 'an enchanted castle'.⁹ Descartes had achieved results quite contrary to those he had intended because, although one of the greatest geometers of his age, he had soon abandoned geometry and the 'geometric spirit' for the esprit de systene. His philosophy was an ingenious romance, his physics a tissue of errors. Galileo was greater than Descartes, since he had not tried to create an imaginary universe, but was content to examine that which existed.¹⁰

Voltaire recognised in Descartes the pioneer of the conception that the esprit geometrique need not remain confined to mathematical sciences but could be extended to all knowledge. He had blazed the trail for the philosophes by addressing his reform not to the academies but to the educated layman. One of Descartes' early works affirmed that his interest did not lie in 'scholastic type' distinctions but in devising rules to serve the contingencies of decision in everyday life." He had not embellished his work with the names of past thinkers, and he emphasised the distinction between erudition and the search for truth. He thought those who were best acquainted with the thinkers of the past were likely to be most infected with their errors and least fitted to receive his novel ideas.¹²

According to Voltaire Newton was superior to Descartes because his discoveries had been made by experience and then confirmed by geometry. In his early 'Philosophical Letters' (1734), Voltaire attempted a lengthy Plutarchian comparison of the two thinkers. He portrayed a Newton who had quickly detected the falsity of the vortices which Descartes had imagined to explain the motion of the planets round the sun and gravitation on the earth. Newton had exploded the notion of such vortices, to his own satisfaction, by rigorous calculation—that guide which had ceased to keep in check the extravagancies of Descartes' lively imagination. Newton had then despaired of any other way of explaining those phenomena. The sight of a falling apple in the solitude of a garden during the Plague year of 1666 had plunged him into a profound meditation, carefully guided by mathematical reasoning. How scrupulous Newton was in not mistaking conjecture for truth was shown by the fact that he rejected the results of those meditations because they did not accord with the faulty measure of the earth then available. Only the revision of that measure prompted him to take up his former calculations again.

Newton's approach, so different from Descartes', was equally evident in his optics, where he had 'anatomised' a single ray of light with more dexterity than the most skilled dissector of a human body. By 'the bare assistance of a prism"³ he had demonstrated that light consisted of a mixture of coloured rays. Descartes had gained immortal fame by mathematically explaining the rainbow, but had then committed himself to a fundamentally erroneous conception of the nature of light.

Voltaire was aware that his comparison would shock his countrymen. They had recognised numerous defects in Descartes' philosophical and scientific ideas. They believed those defects could be remedied. Certainly, they were not generally disposed to replace them with Newton's doctrines. Voltaire dated the beginnings of the decline of the 'Chimerical philosophy' of Descartes in France to 1730.¹⁴ His own conversion to Newton's doctrines had begun during his self-imposed exile in England after his second confinement in the Bastille. The fruits of his sojourn were the Lettres philosophiques (1734), four of which were devoted to Newton. Voltaire depicted a land where the spirit of toleration, reason and good sense prevailed in every sphere of life. He believed that the same spirit of sanity and modesty was evident in the greatest of English thinkers: Bacon, Locke and Newton.

Voltaire said he had found nothing in English thought comparable to the corroding scepticism of Montaigne, La Rochefoucauld's biting satires on human nature, Pascal's tragic pessimism, Malebranche's 'sublime illusions', or the deeply flawed teaching of Descartes. Instead, the English had given the world Bacon's experimental philosophy, Locke's anatomy of the human mind and Newton's great system of the world. In the four letters on Newton, Voltaire described his optical discoveries, explained his ideas of gravitational attraction, assigned to Newton priority in the discovery of the infinitesimal calculus, and had praise even for his Biblical chronology.

The thorniest part of Voltaire's endeavour was the defence of Newtonian attraction. It was precisely in the name of reason that continental thinkers had denounced it. They complained that when Newton and his followers were asked to explain how parts of matter could act on other parts without any material intermediary, they resorted to obscure ideas which involved a continuous divine intervention. 'In the time of Mr. Boyle, nobody would have ventured to publish such chimerical notions,' Leibniz complained to Samuel Clarke in 1716. 'But it is men's misfortune to grow, at last, out of conceit with reason itself, and to be weary of light… What has happened in poetry, happens also in the philosophical world. People are grown weary of rational romances … and they are become fond again of tales of fairies."¹⁵

Voltaire defended Newton against the charge of reviving 'occult' qualities by using arguments that implied a revision of the notion of what constituted a rational explanation. The man who had first traced the ascent of water in a force pump to the pressure of the atmosphere, or of the movement of the arm to muscular contraction, had discovered something new and useful, even if the causes of the elasticity of the air or muscular contraction remained unknown. Newton had shown that the reason why heavy bodies fell towards earth and the planets were retained in their orbits around the sun was a gravitational attraction, and that no subtle matter nor any other force could possibly be involved. It was not necessary for him to have furnished 'the cause of this cause', one of the secrets of God. Voltaire hinted that those who were dissatisfied with Newton's explanations demanded that a rational explanation must be anchored not only in a systematic, but in a complete account of nature, and were falling prey, like Descartes, to the esprit de systéme.¹⁶

One unexpected feature of the Elemens is the extent to which Voltaire commended the Newtonian system of thought for its decisive theological superiority over those of two other leading thinkers, Descartes and Leibniz—unexpected since the 'rational' God of the continental thinkers may, at first sight, appear more congenial to a champion of Enlightenment rationalism. Voltaire did not doubt Descartes' piety, but pointed out how often Cartesians tended to succumb to atheism. 'Give me matter and motion and I shall build you a universe.' How easily could Descartes' proud boast turn into a denial of God's role in creation, as Spinoza's had done! Newton placed no such confidence in the power of puny human reason to reconstruct even a 'likely story' about the way in which God had put together the universe. He had regarded the universe as expressing not rational necessity or a principle of 'sufficient reason', but God's unfettered and sovereign voluntary choice. Fallen man had access only to the results of that choice, as revealed in the arrangement of the world, in the structure and organisation of living things, and in the motions and processes ruling natural phenomena.

Underlying the contrasting ways in which Descartes and Newton studied nature were, thus, to Voltaire's mind, two different ways of conceiving the relation between God and his creation, emphasising either the 'Hellenic' or 'Hebraic' elements in the Christian conception of God. If the stress was on divine reason, then, as Descartes had affirmed, human reason could be said to participate in it whenever it conceived clear and distinct ideas which could then serve as the first principles of an essentially deductive account of nature. Experience would need to be called upon only to decide between alternate ways in which a particular effect mechanically resulted.¹⁷ On the other hand, if the stress was on the divine will, we would be content to study phenomena through experience and experiment, and trace its causes in so far as we could mathematically prove them. It would lead us to renounce the hope of ever attaining the knowledge of ultimate causes or a complete system of knowledge like that envisaged by Descartes or Leibniz.

It was true that the voluntaristic conception of God had been declared unworthy and favourable to atheism. Was not a God who made planets orbit the sun from west to east, and decided upon a particular number of animal species, planets and stars in His universe, like a capricious artisan? Just before the Hanoverian succession, Leibniz had accused Newton of promoting the decay of religion in England by holding such a view of God. God, surely, always chose the best. When Samuel Clarke, who defended Newton's opinions, replied that there were indifferent states of affairs which offered no 'rational' basis for a choice, Leibniz insisted that nowhere in nature was it possible to find two exactly similar things. If God had made things between which differences were 'indiscernible', He would be deprived of 'sufficient reason' for placing one rather than another in a particular place. Clarke retorted that it was exact similarity which made it possible for two individual rays of light to produce the sensation of redness.¹⁸ For Leibniz 'indiscemibleness' detracted from the rationality of God, while for Clarke it served best to express the power and majesty of God.

Voltaire accepted and repeated Clarke's arguments. His preference for a will-theology was also evident in his defence of Newtonian ideas of space and time. Rationalist thinkers had traditionally rejected the conception of space as a featureless void. Descartes, stripping matter to its bare essence, had finally arrived at the clear and distinct idea of 'extension'. Since extension could hardly be the extension of nothing, he had then proceeded to identify space and matter making the universe a plenum. Leibniz said space was nothing but an order of co-existence among things, as time was an order of succession among events. Newton, by contrast, conceived space and time not merely as states of relations but as absolutes. According to Voltaire, Newton's conception served far better to establish the existence and true attributes of God. If the world was finite and contained a void or empty space, then the existence of matter was not a necessity but a result of divine choice. Once matter existed, it had to be extended. There was no such necessity in its possession of powers such as those of gravitational attraction. It had been endowed with them by God's free choice. Newton's world was radically contingent on the divine will. Descartes' world could easily be imagined as self-sufficient. It was 'indefinitely' extended and wholly material, and never ran down because the total quantity of motion in it always remained constant. Newton's conception was therefore far more favourable to establishing the necessity of a divine creator and the utterly dependent nature of matter, and offered the greatest protection against pantheism or materialism.

Why was the Newtonian idea of God as a dominus and the absolute disparity between the divine and human intellects more congenial to Voltaire than the rational supreme architect of Descartes and Leibniz? His bitter experience of persecution for his opinions in France and his reflections on the tolerant atmosphere he had breathed in England had led Voltaire to trace the roots of intolerance to the conviction of being in absolute possession of the truth. Descartes and Leibniz overturned the old dogmatism of the schools, only to fall prey to the esprit de systeme. A moderately sceptical view of the limits of human knowledge, such as the one precisely delineated by Locke, was the best guarantee of freedom of thought.

Voltaire was justified in his belief that Newton attached great value to the theological superiority of his own ideas of space and time over those of Descartes and Leibniz. During his years of exile in England, Voltaire had been close to Samuel Clarke. His testimony is an accurate reflection of the indivisibility of scientific and religious concerns in Newton's circle. 'When I wrote my treatise about our Systeme,' Newton had written to Richard Bentley in 1692, 'I had my eye on such Principles as might work with considering men for the beliefe of a Deity …'¹⁹ The religious ideas appended to the second edition of the Principia were not pious afterthoughts tacked on to a scientific treatise to deflect the criticisms of religious zealots. The union of science and religion is evident in Newton's earliest manuscript remains. It determined his initial response to the teachings of Descartes. In a manuscript dating from the 1670s, Newton rejected Cartesian ideas of matter, of motion and of mind or soul.²⁰

Newton believed that at the heart of Cartesian philosophy lay a radically defective notion of extension, which offered 'a path to atheism'. It was necessary to 'overthrow' it, for only then would it be possible to lay 'truer foundations of the mechanical sciences'.²¹ Descartes had identified extension with matter. But a clear idea of extension revealed it as infinite, uncreated and existing eternally. It was an absolute idea involving no reference to God, and no contradiction was involved when the idea of the existence of matter was combined with that of the non-existence of God. Such an idea of matter paved the way to atheism. The idea of motion which Descartes had adopted (in part to circumvent the Catholic ban on Copernicanism) was purely relative, and took no account of the fact that real forces were involved in true, as distinct from merely relative, motion. It was necessary to refer motion to 'some motionless thing such as extension alone or space in so far as it is seen to be truly distinct from bodies'. Moreover, by his absolute distinction between thinking and extended body, Descartes had rendered the union of mind and body 'unintelligible'.²²

All these grave disadvantages could be avoided by sharply distinguishing space from matter. Extension could be 'clearly conceived', as outside of the world and empty of body. The idea was not one of nothing, but rather an 'excessively clear' one.²³ 'Nothing' had no properties, while extension was uniform and unlimited in length, breadth and depth. It could not be imagined, but could certainly be understood. Once space and matter were distinguished, the idea of matter became indissolubly united with that of God. Space was an 'emanent effect of God' and in that sense necessary. 'If ever space had not existed God at that time would have been nowhere.' Matter existed only because God had so willed: God had 'created the world solely by an act of will'.²⁴

So intensely did Newton wish to downgrade matter that he suggested that it would be possible entirely to do away with the concept of matter or body. Imagine that God had made a portion of space tangible, impenetrable and mobile. It would then have all the properties of body as known to us. It would excite perceptions in created minds and be capable of being moved by them. Even our own power to move what we took to be our bodies could be conceived as a much weaker analogue of the divine power to make empty space impenetrable. Just as God was not space, but contained it 'eminently', so created mind could then also be said 'eminently' to contain body. Newton believed that such a conception of body or matter would explain and confirm 'the chief truths of metaphysics': that God existed, that He had created the world from nothing, and that bodies differ from minds but can combine with them.²⁵

Already in the 1670s Newton was elaborating the array of concepts that he would deploy in the Principia and in the 'General Scholium' added to its second edition: the ideas of absolute space and time, of forces as real entities, and of an analogy between God's creative and sustaining activity and the power of human beings to move their bodies by the exercise of the will.

Voltaire believed that a will-theology served to cut down human pretensions to absolute knowledge. By providing the basis for the empirical and experimental approach of Newton and Locke, it had contributed to the spirit of toleration characteristic of English life. The virtues of a distinct English 'experimental philosophy', free from the opposing dogmatisms attributed to scholasticism and Cartesianism, had already been emphasised by the founders and publicists of the Royal Society soon after the Restoration in 1660. They praised it as the best preservative against the 'enthusiasm' or fanaticism which they condemned as the root cause of civil war and regicide in England. By undermining excessive confidence in opinions, the 'experimental philosophy' would make men more obedient to authority. Bishop Sprat, the Royal Society's first historian, remarked that '… the doubtful, the scrupulous, the diligent Observer of Nature, is nearer to make a modest, a severe, a meek, an humble Christian …'. The Fellows of the Society met every week to witness experiments. They did not speculate prematurely on the causes involved in them beforehand, since they knew how easy it was to fit experiments to preconceptions. When their interpretations of the experiments diverged, no quarrels arose, since they recognised that 'there may be several Methods of Nature, in producing the same Thing, and all equally good'.²⁶ Robert Hooke, who as first Curator of the Society was entrusted with presenting a weekly experiment before the Fellows, agreed that scientific knowledge was likely to grow very slowly. Besides the obscurity of things, there was the added difficulty that 'even the forces of our own minds conspire to betray us'. The only safeguard was in 'the real, the mechanical, the experimental Philosophy…'.²⁷

The myth of an 'experimental philosophy', free from all speculative commitments and presuppositions, deriving theories solely from experiments, was already taking shape in the mid-seventeenth century. It was expressed in a popular and influential form by Sprat. He berated the founders of 'new dogmatisms' who had rejected the ancient varieties of that same distemper, but had then imposed their own theories on men's reason. It reinforced for him the lesson of the English civil war: 'For we also have beheld the Pretenders to publick Liberty, turn the greatest Tyrants themselves.' Sprat obviously included the Cartesians among the new 'dogmatists'. He sharply contrasted the approach of the Royal Society with that of Descartes, who had rejected all he could learn from the senses 'and wholly gave himself over to a reflexion on the naked Ideas of his own mind'. The result was narrow and obscure apprehensions and a wilful ignorance. Very different was the method of the members of the Society, meeting to view experiments, and only then taking it upon themselves to 'judge and resolve upon the matters of fact'. They venerated 'the inartificial process of the Experiment, and not the Acuteness of any Commentary upon it …'. If disputes arose, they were never such as to divide them into factions, since they would be based 'not on matters of speculation or opinion, but onely of sence …'²⁸

Sprat wished to present the 'experimental philosophy' purely as a method. Like any method claiming to lead to truth, it was really anchored in a metaphysic—a set of assumptions about what the world is like and what constitutes a satisfactory and adequate explanation of change. The myth of the 'experiment' as a quasi-religious act, which permitted the true nature of things to be reflected in the cleansed and polished 'mirror of the human mind', occasionally broke down in Sprat's treatise. That is evident in Sprat's discussion of the merits of Sir Christopher Wren, whom he chose as exemplifying the Society's ideal. Sprat gave Wren's reformulation of the Cartesian laws of motion precedence above all his other achievements. Descartes had based them only on 'gross Trials' of tennis and billiard balls, while Wren had devised a special instrument for the purpose and had confirmed his conclusions by hundreds of experiments. Why was so much importance to be attached to the laws of motion and why were they to be regarded as the 'Principles of all Demonstrations in Natural Philosophy'? Sprat's answer is revealing: because '… Generation, Corruption, Alteration, and all the Vicissitudes of Nature, are nothing else but the effects arising from the meeting of little Bodies, of differing Figures, Magnitudes, and Velocities'.²⁹

Such a conception of what nature is like and how all changes in it are to be explained could scarcely have been derived from experiment. Rather, it provided the framework for the interpretation of experiments and, at least in the 'exact sciences' of that time, governed the choice and design of the experiments themselves. The 'mechanical-mathematical' conception of nature which Sprat described had only recently been clearly articulated and no one had contributed more to it than Descartes. It was misleading, therefore, to set up a contrast between a Descartes who began with presuppositions about nature and proceeded to build up a deductive account of natural phenomena, and the English experimental philosophers who were said to have begun with the results of observation and experiment which they then generalised by induction. When discussing the errors of Descartes, Voltaire singled out his laws of motion, his vortices of subtle matter, and his ideas about the nature of light and colour, magnetism and the motion of the heart. It would be difficult to attribute these to a tendency to devise a priori explanations in preference to induction from phenomena. Historians today attribute them, rather, to failures of conceptualisation, or mathematisation, or experimental testing of hypotheses.³⁰ Descartes himself was conscious of many of these deficiencies, but had aimed above all at persuading others that it was possible, in principle, to construct mechanical explanations for all natural phenomena.³¹

The contrast between the English 'experimental philosophy' and the Cartesian philosophy, as propagated by the Royal Society, was accepted fully by Newton in his earliest published work. His paper on light and colours, read before the Society in 1672, seemed like a classic vindication of the 'experimental philosophy'. Wishing to investigate colours, Newton had darkened his chamber and made experiments with a prism. Conclusions 'rigidly' drawn from experimental results were subjected to further experimental tests which culminated in a single 'crucial experiment'. From these experiments, which appeared to have been carried out in a single session, emerged a new theory of colours, overturning all previous ones. Newton had found that each beam of coloured light, as it emerged from the prism on to a screen, had a characteristic index of refraction. He had not been able to change the colour or the degree of refraction by reflection, refraction or other optical means. That was proof, to Newton, that visible 'white' light was a mixture of rays of different colours. A prism separated out the colours, but did not create them by mixing light and shade, as ancient and even contemporary theories held.

Newton's attempt to tailor his account to fit the methodological prescriptions of the dominant 'experimental philosophy' was not entirely successful. Hooke conceded that Newton's discovery of an invariant relation between colour and refrangibility was an important experimental discovery. However, Newton's conclusion that white light was a mixture of colours depended on the hypothesis that light consisted of material particles. Hooke suggested that the experimental results were equally compatible with his own pressure-wave theory. In his reply Newton insisted that he did not need 'to explicate my Doctrine by an Hypothesis' at all, and that what he had asserted was 'most rigid consequence', drawn from 'experiments concluding positively and directly'.³²

Recent historical studies have established that a far longer period of preparation, reflection and trials lay behind the idealised 'historical narration' Newton presented in the paper read before the Society. Only an experimenter with great mathematical competence would have been puzzled, as he said he was, by the fact that an oblong spectrum emerged from the prism instead of the round image of the sun. His experiments were by no means as independent of theories about the nature of light and colours as he maintained.³³ Indeed, theory, experiment and interpretation were so inter-twined in his work—as in that of his other great scientific contemporaries—that they could not adequately be restated in terms of either of the two major conceptions of legitimate scientific method which then prevailed.

By Voltaire's time, Newton's redefinition had given a much greater mathematical tone to the 'experimental philosophy'. Newton's disciple, Colin Maclaurin, wrote that experiments and observations alone could not have enabled Newton to explain causes from effects and then effects from those causes: 'a sublime geometry was his guide in this nice and difficult enquiry.'³⁴ Newton believed that our knowledge is confined to gathering the properties of things from the phenomena, but that we must always seek quantitative laws linking the variations in those properties, because scientific knowledge must assume the form of the most secure knowledge that, besides revelation, we are acquainted with, that of mathematics. The mathematical link between colour and refrangibility of a light ray was an example of such a relationship. 'Hypotheses', to explain why that was so, had an inferior degree of certainty. Similarly, mathematical laws subjecting the motions of gross bodies of the whole machina mundi to precise calculation could be formulated on the assumption that bodies behave as if they attract each other, with a force varying in accordance with a universal law, although the nature of the 'attraction' remained a matter for conjecture. Newton had also relaxed the requirement, prominent in the 'experimental philosophy' of the early Royal Society, that any forces involved in natural phenomena must ultimately be reducible to contact of one body with another, since that was the only kind of action that was intelligible. That criterion led the continental savants to condemn Newtonian attraction. Newton assigned the assertion that 'all the Phaenomena of Nature are purely mechanical' to the class of 'Hypotheses that can never be established by experiments'.³⁵

Newton's modification of the 'experimental philosophy' was grounded in a voluntaristic theology. In the 'General Scholium' added to the Principia he rejected the view that the diversity of things in the world was to be attributed to 'Blind metaphysical necessity'; thus he pointedly dissented from Leibniz's views. That diversity depended, rather, on the 'ideas and will of a Being necessarily existing', a 'living, intelligent, and powerful Being'.³⁶ It is unnecessary to assume that Newton came to favour a voluntaristic conception of God only as the chorus of continental criticisms grew louder. The conception was an important component not only of the 'context of justification' of his gravitational theory, but equally of the 'context of discovery' in which it was formulated. It helped to loosen the tyranny of picturable or 'intelligible' mechanisms upon his conceptual imagination.

What has been said so far may seem to vindicate the historical accuracy of the image of Newton that Voltaire presented in his Elemens. There was, nevertheless, a difference of nuance in Voltaire's enthusiastic adoption and advocacy of Newton's 'experimental philosophy' and its associated theological stance. Newton's attitude had been fashioned in the religious and political atmosphere of mid-seventeenth-century England. Like the Cambridge Platonist thinkers whose arguments found many echoes in his early manuscript writing, 'De gravitatione', Newton regarded it as urgently necessary to revise Cartesian conceptions of matter and motion because they unwittingly lent strong support to the menacing forces of materialism and atheism. His God was the God of Abraham and Isaac, not the cold rationalist principle of Deism.³⁷ In exalting the conception of God as 'pantokrator' in the 'General Scholium' in 1713, he set his face against the temper of a time when the Church of England was relaxing the requirements of belief it demanded from its flock.

Voltaire, on the other hand, was not really aiming to overwhelm the individual consciousness with an image of God of will and power continually and most intimately involved in the universe He had created. Voltaire chose to emphasise human insignificance in the vastness of the universe rather than divine immensity.³⁸ His fervent promotion of the Newtonian God of will and power was not aimed primarily at countering materialism and atheism. Voltaire regarded the greatest threat to freedom of thought as originating in grandiose systems of thought, made binding by authority on pain of persecution. Cartesianism was the latest example of that menace. A repressive church had first unsuccessfully tried to stifle its influence in France, but later came to embrace it as the basis for a new theology. Malebranche had reconciled Descartes with orthodox faith. Amauld and Bossuet came to see Cartesianism as a new version of the philosophia perennis of Plato and St. Augustine. It was the same Bossuet, tutor to the Dauphin, who had condemned scepticism and toleration as twin monsters bred by the Reformation.³⁹ Traditionally, a will-theology had served to demolish the pretensions of a rational theology. In Voltaire's hands, it was turned against all grand systems of thought. The esprit de systeme, most recently expressed by Descartes and Leibniz, must itself be extirpated. The 'experimental philosophy' would make it impossible to set up any new dogma and would fatally weaken the power of authority to suppress free thought and to bar the way to human progress and happiness. Voltaire would enthusiastically have approved Maclaurin's verdict on the Cartesian philosophy: '… the foundation is so faulty, and the whole superstructure so erroneous, that it were much better to abandon the fabrick, and suffer the ruins to remain a memorial, in all time to come, of the folly of philosophical presumption and pride.'⁴⁰

Voltaire had fully recognised the intimate link binding Newton's view of God and his conception of 'experimental philosophy', but he would have found uncongenial some other implications which. flowed from Newton's will-theology. Newton believed that God's hidden will was revealed to fallen man not only in the structure and workings of nature, but in the unfolding course of history. By comparing historical events with Biblical prophecy, it was possible to demonstrate that the future had been foretold in minute detail. Newton devoted a great deal of his energy to such an enterprise, with the aims of confuting those who scoffed at religion and of securing the Protestant reliance on the Bible against the Catholic Counter-Reformation onslaught.⁴¹ Knowledge about history was hidden in the Bible but could be seen to be there only retrospectively. So, too, truths about nature were concealed in ancient bodies of wisdom, but their full meaning would become clear only when they had been 'inductively' rediscovered. The Pythagorean 'harmony of the spheres' was really an enigmatic representation of Newton's law of universal gravitation; the literature of alchemy contained hints of the active principles which operated in nature.⁴²

With the growing influence of Voltaire's image of Newton as the founder of a new kind of rationalism, which had supposedly broken free of theology and metaphysics and required nothing but the immediate testimony of the senses to build up its picture of the world, the integration of the religious and the scientific in Newton's thought became increasingly incomprehensible to succeeding generations. To Biot and Laplace, Newton's monumental labours in Biblical prophecy appeared so eccentric that they were tempted to regard them as proof that Newton's famous mental collapse of 1693 had left his intellect gravely impaired. Those charges were refuted by Sir David Brewster, who published the first comprehensive life of Newton in 1855 when the Darwinian storm lay in the future, and the alliance between science and religion in England through natural theology remained intact. But work on Newton's manuscripts shocked Brewster by revealing an aspect of Newton's thought that he, too, found irrational: the study of alchemy to which he had found Newton had devoted a great portion of his most creative years.⁴³

The 'Newton industry' of the last few decades has given us much deeper knowledge of many diverse facets of Newton's life and work on the basis of his great manuscript remains, but without fully reconciling what seems 'rational' and 'irrational' to us in Newton's thought.⁴⁴ It is only by going beyond Voltaire's image to that seventeenth-century milieu in which Newton's intellectual formation took place that we can hope to bring together all that recent scholarship has discovered in a truer likeness of Isaac Newton.

Notes

¹ Huygens, Oeuvres Completes (The Hague 1888-1950), IX, 538.

² H. G. Alexander (ed.), The Leibniz-Clarke Correspondence (Manchester 1956), 11-12.

³Journal (1688), cited in P. Mouy, La Developpement de la Physique Cartésienne (Paris 1934), 256.

⁴ Cited by P. Burnet, L'Introduction des Théories de Newton en France au XVII' siècle (Paris 1931), 9.

⁵ A. Mansion, Introduction a la Physique Aristotelienne (Louvain-Paris 1945), 134-8.

⁶ 'Lettres philosophiques', in Oeuvres Completes (Paris 1879), XXII, 132.

⁷ Letter to Comte des Alleurs, 1736, in ibid., XXXV, 51.

⁸ 'Siècle de Louis XIV', in ibid., XIV, 534.

⁹ Ibid., XXXV, 51.

¹⁰ Ibid., XXXV, 52.

¹¹ Descartes, Philosophical Works; tr. Haldane & Ross (Cambridge 1931), 'Regulae', 1, 2.

¹² 'Principia philosophiae', in ibid., I, 209.

¹³ Letter XVI, in Oeuvres Completes, XXII, 141.

¹⁴ Ecrivains francais du siècle de Louis XIV', in ibid., XIV, 63.

¹⁵ Alexander, Leibniz-Clarke Correspondence, 92.

¹⁶Oeuvres Complètes, XXII, 131.

¹⁷ G. Buchdahl, Metaphysics and the Philosophy of Science (Oxford 1969), 79-180.

¹⁸ Alexander, op. cit., esp. 97-101.

¹⁹ Newton, Correspondence (Cambridge 1959), III, 233.

²⁰ 'De gravitatione', in A. R. and M. B. Hall (eds & trs), Unpublished Scientific Papers of Isaac Newton (Cambridge 1962), 89-156.

²¹ Ibid., 131.

²² Ibid., 143.

²³ Ibid., 132.

²⁴ Ibid., 141.

²⁵ Ibid., 142.

²⁶ Sprat, The History of the Royal Society of London (London 1702 edn), 92.

²⁷ Hooke, Micrographia (London 1665), Preface.

²⁸ Sprat, op. cit., 95-7, 91-2.

²⁹ Ibid., 312.

³⁰ P. Mouy, op. cit., 1-71; R. S. Westfall, Force in Newton's Physics (London-New York, 1971), 56-98; Buchdahl, op. cit., 79-180.

³¹ Mouy, La Developpement de la Physique Cartésienne, 142.

³² I. Bernard Cohen (ed.), Isaac Newton's Papers and Letters on Natural Philosophy, second ed. (Cambridge, Mass.-London 1978), 123.

³³ Recent studies are listed in ibid., 499-501.

³⁴ C. Maclaurin, An Account of Sir Isaac Newton's Philosophical Discoveries, seconded. (London 1750), 8.

³⁵ A. Koyré and I. B. Cohen, 'Newton and the Leibniz-Clarke correspondence', Arch. inter. d'Hist. des Sc., XV (1962), 114.

³⁶ A. Motte and F. Cajori (eds & trs), Mathematical Principles of Natural Philosophy (New York 1969), II, 546.

³⁷ Frank E. Manuel, The Religion of Isaac Newton (Oxford 1974).

³⁸ p. Pomeau, La Religion de Voltaire (Paris 1969), 215; J. Erhard, L'Idee de Nature en France dans la Premiere Moitie du XVII' Siècle (Paris 1963), 133ff.

³⁹ Bossuet, 'Defense de l'Histoire', in Oeuvres Choisies (Nimes 1785), III, 425.

⁴⁰ Maclaurin, op. cit., 82.

⁴¹ Frank E. Manuel, Isaac Newton, Historian (Cambridge 1963).

⁴² J. E. McGuire and P. M. Rattansi, 'Newton and the "Pipes of Pan" ', Notes & Records Roy. Soc. Lond., XXI (1966), 108-43; B. J. T. Dobbs, The Foundations of Newton's Alchemy (Cambridge 1975).

⁴³ Brewster, Memoirs of the Life, Writings and Discoveries of Sir Isaac Newton (Edinburgh 1855), II, 374-5.

⁴⁴ R. S. Westfall, 'The changing world of the Newtonian industry', Journ. Hist. Ideas, XXXVII (1976), 175-86; Cohen, Papers, 498-504.