Let us indicate, in its essential features, the change of mind produced by the prodigious success and by the diffusion of Newton’s celestial mechanics: at the beginning of the 18th century, a sort of Cartesian orthodoxy reigned almost everywhere in the world; Rohault’s physics was widespread everywhere. In the space of thirty years, she had disappeared everywhere; England abandoned it first; in Scotland, it lasted until 1715: “I believe,” wrote Reid (August 24, 1787), speaking of James Gregory, professor at the University of Saint Andrews, “that he was the first professor of philosophy to teach the doctrine of Newton at a university in Scotland; for the Cartesian system was the orthodox system at that time and continued to be so until 1715.” And Voltaire, who, with Maupertuis, did so much to spread the Newtonian spirit in France, considers the year 1730 as the date of its definitive success: “It is hardly,” he writes, thinking of the philosophy of Descartes, “that since the year 1730 we began to return in France from this chimerical philosophy, when geometry and physics experiments have been more cultivated.” It was on this date that, despite Fontenelle’s loyalty to the Cartesian discipline, the Newtonians were introduced to the Academy of Sciences. Later, in 1773, Holland was able to write of the philosophy of Descartes: “One would hardly find any followers of it today.”
Newton’s celestial mechanics is characterized by two features which are precisely the opposite of those we have recognized in Cartesian physics: an extreme precision in the application of mathematics to natural phenomena, which makes it possible to rigorously calculate major cosmic phenomena (movement of planets, gravity, tides) when their initial conditions are given; a very vast margin left for the inexplicable, since these initial conditions cannot be mathematically deduced, but only given by experience. In Descartes, on the contrary, a mechanical explanation, which wanted to be integral, was juxtaposed, in particular cases, with qualitative descriptions of mechanisms, which did not lead to any prediction.-Now, these two features, in Newton, are united: the first of them depends on the invention of the calculation of fluxions; this calculation, the only adequate language of the new mechanics, expresses not only, like analytical geometry, what is the state of a quantity at a given instant, but also how it varies at that instant in intensity and in direction. But, and this is the second feature, the conditions which make possible the application of this calculation to physical reality are not contained in this calculation itself: we can easily imagine such conditions which, if they had been carried out, would have made the use of this calculation and the discovery of the law of attraction completely impossible; in current circumstances, in fact, the position of a planet in relation to the sun is such that the attraction of the other bodies of the universe on it is negligible compared to the attraction of the sun, so that the calculation has to consider the reciprocal attraction of two masses; but suppose that the disturbing causes were of the same order of magnitude as the solar attraction, in this chaos of reciprocal actions (that of Leibniz’s world, where everything depends on everything), the calculation would have been without application.
Among the initial conditions, however, there are some which could have been different without the mechanical problem ceasing to be soluble; it is indifferent, for example, whether the tangential component of the movement of the planets has one direction or the opposite direction.
These two features are inseparable: the solution to the problems of celestial mechanics requires mechanically inexplicable data: in other words, there is no cosmogony in Newton, that is to say a scientific explanation of the origin of the current relationships of position and speed of the celestial bodies: as the astronomer Faye says, “Newton is stopped dead in the face of the constitution of the gyratory origin of the solar system” (1) But how can we interpret this sort of empty space left by the explanation? Recourse to chance is impossible; if we suppose planets thrown randomly into the gravitational field of the sun, there is an infinitely small probability that they take their current position and movement: we must come to the power of an intelligent being who gave the impetus to the planets, and who, to create isolated solar systems, “placed the fixed stars at an immense distance from each other, lest these globes fall on each other by force of their gravity” (2).
- Quoted by BUSCO, Les Cosmogonies Modernes, p. 52, Paris, 1924.
- Léon Bloch, La Philosophie de Newton, p. 502 sq., Paris, 1908.
Source: Émile Bréhier(1951). Histoire de la philosophie, Presses Universitaires de France. Translation and adaptation by © 2024 Nicolae Sfetcu
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