The Frenchman Jean Le Rond d’Alembert (1717–1783) is one of the most brilliant thinkers of the Enlightenment. Mathematician, physicist and philosopher, he also made important contributions to astronomy: he was the first to explain the phenomenon of the precession of the equinoxes from Newton’s laws by means of precise calculations. One of the craters on the Moon is named after him.
His interest in music led him to discover the wave equation, the mathematical formula that describes vibrating bodies such as guitar strings. This discovery created a new area of mathematics, the theory of partial differential equations, one of the most important to date.
Another very important contribution is D’Alembert’s Theorem, also called the Fundamental Theorem of Algebra: every polynomial equation of degree N has exactly N solutions in the set of complex numbers. Students of calculus are also familiar with D’Alembert’s criterion for the convergence of infinite series.
In physics, apart from the development of wave theory, his main contribution was the publication of the Treatise on Dynamics, a fundamental step in the mathematical formalization of Newton’s ideas, a precursor to the works of Lagrange and Laplace. At the base is the so-called d’Alembert Balance Principle, also well known to graduate students.
Outside the scientific world, d’Alembert is best known for being, with Denis Diderot, co-editor of the “Encyclopedia”, an ambitious initiative to collect the knowledge of the time and make it accessible to all. D’Alembert brought this great work, a symbol of the Enlightenment, to life from the beginning until 1757, when he fell out with Diderot.
And yet, the beginning of his life could not have been less promising. Born of a temporary relationship between his mother, Claudine de Tencin, and an aristocrat, possibly the knight Louis-Camus Destouches, he was abandoned the day after his birth on the steps of the Saint-Jean-le-Rond chapel (after which he was named). .
Retrieved from father, given to Hospice for Found Children and, later, to an adoptive family. Destouches left him a small annual income in his will, which ensured his survival and allowed him to carry out his studies.
In 1772, D’Alembert became permanent secretary of the French Academy of Sciences. Today, it is a position with fixed mandates – the current holder is the mathematician Étienne Ghys, a great friend of Brazil – but then the name was taken seriously: D’Alembert stayed in the position until he died.
As the abbot of Saint-Germain l’Auxerrois refused to bury a sworn atheist in his church, his body was accompanied by a long procession to the Cemetery des Porcherons (later deactivated), where he was buried in a mass grave.
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