Newtonianism in the French Enlightenment

Rob Iliffe is Professor of Intellectual History and the History of Science in the Department of History at the University of Sussex. He has written the Very Short Introduction to Newton and directs the online Newton Project. On 28 February 2015 he gave a fascinating talk at the ‘Voltaire and the Newtonian Revolution’ conference that explored the fate and legacy of Newton’s scientific views in eighteenth-century France of which this is a brief summary.

Newton_frontispiece

Soon after Newton had published his initial work on the heterogeneity of white light (in 1672), he became embroiled in a series of disputes about the truth of his theory, and about the facts on which it was based. Edme Mariotte’s failure to reproduce aspects of Newton’s ‘crucial experiment’ in 1681 influenced the negative opinion of Newton’s work by many French physicists, although there was increased interest in his work at the Académie des Sciences following the publication of his Optice in 1706. There was also opposition to the physical theories and epistemological claims expressed in his Principia Mathematica, and many commentators continued to prefer the Cartesian doctrine of tourbillons to the notion of ‘attraction’ that underlay Newton’s theory of universal gravitation.

Pierre Louis Moreau de Maupertuis (1698-1759). Source gallica.bnf.fr / Bibliothèque nationale de France

Pierre Louis Moreau de Maupertuis (1698-1759). Source gallica.bnf.fr / Bibliothèque nationale de France

A delegation of French natural philosophers visited England in 1715 and were treated to a number of experiments that confirmed Newton’s theories. However, it was Newton’s death in the spring of 1727, and Bernard de Fontenelle’s influential Eloge that followed, that triggered a serious spurt of interest in his work. Two men, Voltaire and Pierre Moreau de Maupertuis wrote popular works in the early 1730s that brought the nature and revolutionary scope of Newton’s ideas to a much larger audience. Yet it was not until the results of a French scientific expedition to Lapland were announced in 1737 that the public really began to switch allegiance to the Newtonian worldview. This excursion, led by Maupertuis, left France in 1736 to measure the length of a degree, one year after another voyage had set out to perform similar cartographic measurements in Peru (now Ecuador). The results from the Finnish expedition, and indications from the ill-fated trip to Peru, showed that the earth was flattened at the poles (as Newton had argued), and was not a prolate spheroid as many Cartesians had claimed.

Newtonianism was duly adopted and made the central plank of their paean to Enlightenment by men such as Voltaire and Jean Le Rond D’Alembert. Newton’s attacks on arbitrary and fictitous ‘hypotheses’ and ‘systems’ were reconfigured to serve in the general assault on the ‘infamy’ of persecution and superstition. There were some problems with the approach, firstly because Newtonianism could be used (as the British largely did) to defend the idea of an intelligent Creator God, and secondly because Newton himself was clearly both devout and a serious student of theology. While the latter could be explained away as the result of senility or dilettantism, there was always the danger that Newton himself could be deified as the founder of Reason. This possibility was explored in the majestic designs for a Cenotaph to Newton created by Etienne-Louis Boullée in the mid-1780s, and in the early plans for a ‘Church of Newton’ described by Henri de Saint-Simon at the start of the following century.

– Rob Iliffe, Director of the Newton Project

Cross-section of a ‘Newton cenotaph’ by Etienne-Louis Boullée. Source: gallica.bnf.fr / Bibliothèque nationale de France

Cross-section of a ‘Newton cenotaph’ by Etienne-Louis Boullée. Source: gallica.bnf.fr / Bibliothèque nationale de France

Strange skies: Voltaire’s physics

Letter XIV of Voltaire’s Lettres philosophiques provides an insight into the early days of modern science, contrasting the theories of Descartes and Newton at a time in which Newtonian physics was new and controversial. The vitality of the debate as approached in this volume struck me, as a humanities student, more intensely than GCSE science lessons ever managed to; it made me realise that even the laws of gravity were a new discovery once.

VA39_Tourbillons

‘Figure des tourbillons de Descartes’, in Voltaire, La Henriade, divers autres poèmes etc. [Geneva, Cramer and Bardin], 1775, 37 vol., vol.26, facing p.355.

However, it was the way in which Descartes’ world was depicted that left a greater mark on me, through its apparent strangeness (although, had I heard about it in a physics classroom, no doubt it would seem as banal as gravity). In Voltaire’s portrayal, the emphasis is on movement, ‘tourbillons de matière subtile’,[1]  next to which our modern conception of gravity seems, if more accurate, somehow less dynamic. This theoretical universe is a crowded one, where light ‘existe dans l’air’ and the dominant forces are pushing ones; Newton’s is an elegant void, where movement is due to attraction.

After studying the letter, I wrote the poem below, inspired both by the painterly quality of Voltaire’s images, and the way in which reading it had offered me a new perspective on the way human knowledge changes. Letter XIV typifies a time very different from our era of specialization, where science and the humanities are carefully cordoned off from one another. Voltaire was spreading something that was, at that time, revolutionary, and it seems unlikely nowadays that a literary figure could be so fully involved with the cutting edge of science. I wanted to capture this sense of change, and the related fact that, while these competing explanations for the universe once ranked side by side, one has now been relegated to the status of image, while the other has become (relatively) unquestioned scientific fact.

Descartes thought the sky was made of spirals,
spangled whirlwind scrawls, a tide of starlight,
oily brushstrokes crowding in the midnight,
currents sweeping past the moon. His rival,
a Mr Newton, won; the Lumières jeered,
and though the sciences were an art those days,
the pictures Descartes saw were just a phase,
an early Van Gogh in the wrong career.

StarryNight_VanGogh

The Starry Night, by Vincent Van Gogh, 1889.

– Rowan Lyster

(Poem first published in the ISIS magazine, Oxford)

[1] All quotes are from Letter XIV, Lettres philosophiques.