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Voltaire: Experimental Philosopher

Voltaire, détail du visage (château de Ferney)

Voltaire, détail du visage (château de Ferney)

Peter Anstey writes …

The French Philosophe Voltaire played an important role in the transmission of experimental natural philosophy to France in the 1730s. That Voltaire regarded the emergence of experimental philosophy as a pivotal moment in history is seen in his history of The Age of Louis XIV (1751). In the Introduction to this work he speaks of the Italians of the Renaissance being ‘in possession of everything that was beautiful, excepting music, which was then in but a rude state, and experimental philosophy, which was everywhere unknown’.

The decisive moment came in the early seventeenth century in the writings of Francis Bacon. For, in his Letters Concerning the English Nation (Oxford, 1994) that appeared in English and French in 1734, Voltaire credits Bacon with being the first experimental philosopher:

He is the Father of experimental philosophy … no one, before the Lord Bacon, was acquainted with experimental Philosophy, nor with the several physical Experiments which have been made since his Time. (pp. 51–2)

But did Voltaire himself take up experimental philosophy or was he merely a herald and conduit for this movement to the French reading public?

Two works suggest that Voltaire fully embraced the new experimental philosophy that he had encountered in England in the 1720s. The first is his Treatise on Metaphysics that he wrote in 1734, the year in which his Letters appeared but which was published posthumously. This work bears the marks of someone who had imbibed the methodological position of the new experimental philosophy both in its rejection of speculative philosophy and hypotheses and the priority it gives to observation and experiment. For example, he says:

It is clear that one should not make hypotheses. We ought not to say ‘Let us begin by inventing some principles with which we will try to explain everything’, but we ought to say, ‘Make an exact analysis of things and then we will try with great diffidence whether they are related to certain principles’.

He goes on to claim ‘when we can help ourselves with neither the compass of mathematics, nor the torch of experiment and natural philosophy, it is certain that we are not able to do anything’ (ibid., p. 301).

The second work is his ‘Essay on the nature of fire and its propagation’, an essay he submitted for the Académie des sciences prize in 1738. As things turned out Leonhard Euler’s essay won the prize, but Voltaire’s submission and that of Madame du Châtelet were published alongside Euler’s winning essay in the Recueil des pieces qui ont remporté le prix de l’Académie royale des sciences in 1739. This is Voltaire’s only serious foray into experimental natural philosophy.

In the Part One of the essay, the part that addresses the nature of heat, he uses the experiments of others to argue for an Aristotelian theory of heat as an element. In doing so he cites the experimental work of Boyle, Newton and Boerhaave. However, in the second article of Part Two of the essay, on the subject of how fire acts on other bodies, Voltaire relates a whole series of experiments that he had performed himself. This is with a view to establishing certain laws by which fire acts, the second of which purported laws is an inverse square law analogous to Newton’s law of gravitational attraction! (p. 201) At one point he tells us:

the comparative degrees of heat of fluids of minerals and of vegetables can, I believe, be known with the aid of a single thermometer constructed on the principles of Mr de Réaumur.

There is only one precaution to take, and this is that the spirit of wine should not boil in the thermometer. To achieve this I plunged only up to half of the ball of the thermometer in the boiling liquors. (p. 207)

Much more could be said about this fascinating essay, but the key point of interest here is that it is a demonstration of Voltaire’s commitment to and practice of experimental natural philosophy.

He may never have experimented again, yet he continued to refer to experimental philosophy, alluding to his essay on heat in his Metaphysics of Newton (La métaphysique de Neuton, Amsterdam, 1740, p. 49) and, most famously, referring to experimental philosophy in his literary works, including Candide (1759) and Micromégas (1752).


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