Jean le Rond d'Alembert

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French mathematician, encyclopedist, and philosopher (1717–1783)

D'Alembert was the illegitimate son of a Parisian society hostess, Mme de Tenzin, and was abandoned on the steps of a Paris church, from which he was named. He was brought up by a glazier and his wife, and his father, the chevalier Destouches, made sufficient money available to ensure that d'Alembert received a good education although he never acknowledged that d'Alembert was his son. He graduated from Mazarin College in 1735 and was admitted to the Academy of Sciences in 1741.

D'Alembert's mathematical work was chiefly in various fields of applied mathematics, in particular dynamics. In 1743 he published his Traité de dynamique (Treatise on Dynamics), in which the famous d'Alembert principle is enunciated. This principle is a generalization of Newton's third law of motion, and it states that Newton's law holds not only for fixed bodies but also for those that are free to move. D'Alembert wrote numerous other mathematical works on such subjects as fluid dynamics, the theory of winds, and the properties of vibrating strings. His most significant purely mathematical innovation was his invention and development of the theory of partial differential equations. Between 1761 and 1780 he published eight volumes of mathematical studies.

Apart from his mathematical work he is perhaps more widely known for his work on Denis Diderot's Encyclopédie as editor of the mathematical and scientific articles, and his association with the philosophes. D'Alembert was a friend of Voltaire's and he had a lively interest in theater and music, which led him to conduct experiments on the properties of sound and to write a number of theoretical treatises on such matters as harmony. He was elected to the French Academy in 1754 and became its permanent secretary in 1772 but he refused the presidency of the Berlin Academy.

The chief contribution by the French mathematician and physicist Jean le Rond d'Alembert (1717-1783) is D'Alembert's principle, in mechanics. He was also a pioneer in the study of partial differential equations.

Jean le Rond d'Alembert was born on Nov. 16, 1717, and abandoned on the steps of the church of St-Jean-le-Rond in Paris. He was christened Jean Baptiste le Rond. The infant was given into the care of foster parents named Rousseau. Jean was the illegitimate son of Madame de Tencin, a famous salon hostess, and Chevalier Destouches, an artillery officer, who provided for his education. At the age of 12, Jean entered the Collège Mazarin and shortly afterward adopted the name D'Alembert. He became a barrister but was drawn irresistibly toward mathematics.

Two memoirs, one on the motion of solid bodies in a fluid and the other on integral calculus, secured D'Alembert's election in 1742 as a member of the Paris Academy of Sciences. A prize essay on the theory of winds in 1746 led to membership in the Berlin Academy of Sciences. D'Alembert wrote the introduction and a large number of the articles on mathematics and philosophy for Denis Diderot's Encyclopédie. He entered the Académie Française as secretary in 1755.

D'Alembert had a generous nature and performed many acts of charity. Two people especially claimed his affection; his foster mother, with whom he lived until he was 50, and the writer Julie de Lespinasse, whose friendship was terminated only by her death. D'Alembert died in Paris on Oct. 29, 1783.

Rigid Body and Fluid Motion

D'Alembert's principle appeared in his Traité de dynamique (1743). It concerns the problem of the motion of a rigid body. Treating the body as a system of particles, D'Alembert resolved the impressed forces into a set of effective forces, which would produce the actual motion if the particles were not connected, and a second set. The principle states that, owing to the connections, this second set is in equilibrium. An outstanding result achieved by D'Alembert with the aid of his principle was the solution of the problem of the precession of the equinoxes, which he presented to the Berlin Academy in 1749. Another form of D'Alembert's principle states that the effective forces and the impressed forces are equivalent. In this form the principle had been applied earlier to the problem of the compound pendulum, but these anticipations in no way approach the clarity and generality achieved by D'Alembert.

In his Traité de l'équilibre et du mouvement des fluides (1744), D'Alembert applied his principle to the problems of fluid motion, some of which had already been solved by Daniel Bernoulli. D'Alembert recognized that the principles of fluid motion were not well established, for although he regarded mechanics as purely rational, he supposed that the theory of fluid motion required an experimental basis. A good example of a theoretical result which did not seem to correspond with reality was that known as D'Alembert's paradox. Applying his principle, D'Alembert deduced that a fluid flowing past a solid obstacle exerted no resultant force on it. The paradox disappears when it is remembered that the inviscid fluid envisaged by D'Alembert was a pure fiction.

Partial Differential Equations

Applying calculus to the problem of vibrating strings in a memoir presented to the Berlin Academy in 1747, he showed that the condition that the ends of the string were fixed reduced the solution to a single arbitrary function. D'Alembert also deserves credit for the derivation of what are now known as the Cauchy-Riemann equations, satisfied by any holomorphic function of a complex variable.

Research on vibrating strings reflected only one aspect of D'Alembert's interest in music. He wrote a few of the musical articles for the Encyclopédie.

He favored the views of the composer Jean Philippe Rameau and expounded them in his popular Élemens de musique théorique et pratique (1752).

Further Reading

D'Alembert's more important mathematical works are available in English, as are his many contributions to the Encyclopédie, the most significant of which is his Preliminary Discourse. His contributions are discussed in Thomas L. Hankins, Jean d'Alembert: Science and the Enlightenment (1970; reprinted, 1990). Excellent studies on D'Alembert as a philosophe are Ronald Grimsley, Jean D'Alembert (1963), and John Nicholas Pappas, Voltaire and D'Alembert (1962). The standard biography, in French, is Joseph Bertrand, D'Alembert (1889). A full account of D'Alembert's work in dynamics appears in René Dugas, A History of Mechanics (1950; trans. 1955).

Alembert, Jean le Rond d' (1717-83). French mathematician, scientist, and man of letters. The illegitimate son of Madame de Tencin, he was left at birth outside the church of Saint-Jean-le-Rond, Paris—whence his second name. He was brought up by a glazier's wife, Madame Rousseau, remaining close to her as long as she lived. He never married. Contemporary accounts and his letters show him as an entertaining, irreverent companion, but little of this can be seen in his published works.

His precocious genius for mathematics led to his early admission to the Académie des Sciences, and in 1743 he published the Traité de dynamique, which incorporates the principle for which his name is remembered in the history of mechanics. Further scientific works followed on a number of topics in physics, including the movement of fluids and the cause of winds. It was as an eminent scientist that he was invited to co-edit the Encyclopédie with Diderot. In 1758, when the work ran into difficulties, he withdrew, but his contribution was an important one. In addition to overseeing the scientific and mathematical section, he wrote entries on general topics, including an attack on current secondary schooling (‘Collège’) and an appeal for the creation of a theatre in Geneva (‘Genève’), which provoked Rousseau's Lettre à d'Alembert. Above all, he composed the ‘Discours préliminaire’, a central text of the French Enlightenment; it combines an analytic account of the acquisition of knowledge with a triumphalist picture of the development of enlightened thinking over the preceding two centuries.

In 1754 he became Secrétaire Perpétuel of the Académie Française. He used this position to promote the philosophe cause and sought to enhance the Academy's dignity with his Histoire des membres de l'Académie Française (1785-7), which contains numerous éloges of deceased Academicians, including Fontenelle and Montesquieu. In the 1750s and 1760s he also composed essays on many general topics, including style and language—see his Mélanges de philosophie, d'histoire et de littérature. His important Essai sur la société des gens de lettres avec les grands (1753) shows his desire to defend the autonomy of writers against the demands of polite society. Apparently a free-thinker, he was an ally of Voltaire in his anti-clerical campaigns, and was active in stirring up opinion against the anti-philosophe Jean-Jacques Rousseau.

[Peter France]

Bibliography

• R. Grimsley, Jean d'Alembert (1963)

D'Alembert, Jean le Rond (1717-83) French mathematician and philosopher. Although he achieved his distinction as a mathematician, in philosophy D'Alembert is remembered as one of the greatest figures of the French Enlightenment. Together with Diderot he was the moving force behind the Encyclopédie. His own philosophy placed total faith in natural science, although like Locke before him he tempered his empiricism with confidence in a rational structure to both the natural and the ethical domain. There is some evidence that D'Alembert progressed from a tentative theism, based upon the distinct nature of intelligence and the impossibility of it emerging in a purely material universe, to an atheistic and materialist view of the world. There are many testimonies to his virtuous and philosophical character, and Hume entirely entrusted to him the conduct of his dispute with Rousseau.

Alembert, Jean Le Rond D' (1717–1783), French mathematician, scientist, philosopher, and writer. Born 17 November 1717, Jean Le Rond d'Alembert was the illegitimate son of the famous Claudine Alexandrine Guérin, marquise de Tencin, and an artillery officer, Louis-Camus Destouches. Abandoned on the steps of Saint-Jean-Le-Rond in Paris, he was taken to the Foundling Home and named after the church where he was discovered. Through his father's efforts he was placed with a foster mother, Mme. Rousseau, to whom he remained devoted. His father also saw to it that his son received a good education; he attended first a private school, then the Collège des Quatre-Nations. After three years studying law and medicine, it became clear to d'Alembert that mathematics was his true vocation. In 1741 he was named an adjoint (adjunct) at the Academy of Sciences, and in 1743 he published his most important mathematical work, the Traité de dynamique (Treatise on dynamics). In addition to six other major scientific treatises, his 1752 Éléments de musique, théorique et pratique, suivant les principes de Rameau (Elements of practical and theoretical music following Rameau's principles) is noteworthy as a lucid exposition of Rameau's hugely influential harmonic theory.

Today d'Alembert is somewhat undervalued, remembered mostly as coeditor of the Encyclopédie, although even in that enterprise he was eclipsed by Denis Diderot (1713–1784). In his day d'Alembert was esteemed second only to Voltaire (1694–1778) in leading the philosophe movement, the very core of Enlightenment ideology. Through his role in the French Academy, to which he was elected in 1754, and of which he became permanent secretary in 1772, the discreet and cautious d'Alembert was able to confer legitimacy on many of the philosophes' deepest concerns while remaining immune to the imprisonments and exiles that punctuated the lives of so many of his colleagues.

Largely because of his scientific reputation, but also because he was a popular, brilliant participant in Parisian salons, d'Alembert was asked as early as 1745 to participate in the production of the Encyclopédie; in 1747 he was named coeditor with Diderot and was charged primarily with the mathematical and scientific articles. His nonscientific entry, the infamous "Genève," created a controversy with Jean-Jacques Rousseau (1712–1778) and then with Genevan Protestants, leading d'Alembert to resign from his editorial post in 1758.

The desire to avoid scandal at all costs, which led to his resignation, was consistent with the public comportment d'Alembert adopted for the rest of his career. Although he shared many of the goals of the other philosophes, his correspondence (in particular with Voltaire) consistently shows not only a refusal to jeopardize his career and freedom to remain in Paris but also an unflinching conviction that enlightenment must be a gradual and tactful process of persuasion rather than a series of attacks, whether open or anonymous. He thought he could best serve that end by promoting the philosophe party at large and especially in the Academy, by mediating disputes within the group and by functioning as a de facto public relations manager as a foil to the polemical outpourings from Voltaire at Ferney and from numerous other quarters (most notably the baron Paul Thiry, baron d'Holbach; 1723–1789). Indeed, it had long been Voltaire's wish that when he died, d'Alembert would succeed him as leader of the philosophes. Much of d'Alembert's immense stature in the eighteenth century, then, came not from his writings but from his ceaseless efforts to unite and promote his colleagues and advance their mutual cause.

In 1759 he laid out his philosophical principles and methodology in his Essai sur les éléments de philosophie: ou sur les principes des connaissances humaines (Essay on the elements of philosophy, or on the principles of human knowledge). In this work he provides a synthesis of his prior thought in epistemology, metaphysics, language theory, science, and aesthetics. The Éclaircissements (Explanations), added in 1767, round out the Essay, forming a composite that represents the ambitious scope of d'Alembert's empiricist philosophy.

However, his most important work is without doubt the 1751 Preliminary Discourse to the Encyclopedia. In this concise and occasionally flawed but often brilliant document, d'Alembert seeks to justify the encyclopedic enterprise in a Lockean vein, by showing the unity of all thought from its sensorial origins (in "direct" and "reflected" ideas deriving from corporeal impressions). However, he also attempts to provide a rational, scientific method for the mapping of human knowledge as well as a historical account of the evolution of human thought. The result is not merely an apology for the ends as well as the means of the Encyclopédie, it is also a superb summation of Enlightenment empirical and sensualist thought, a forceful rejection of Cartesian metaphysics (if not Cartesian method, which d'Alembert admired), and a valorization of the scientific method of Francis Bacon (1561–1626) and (particularly) Isaac Newton (1642–1727). In the Discourse, d'Alembert succeeds in showing the intimate connection between the spirit of the Encyclopédie and the concerns of the Enlightenment generally, in a way that is not always obvious to the reader of the encyclopedia's articles themselves.

D'Alembert's last important work, the fifth volume of Mélanges de littérature, d'histoire, et de philosophie, was published in 1767. From that point on, his health became increasingly fragile. In his last years he wrote little, instead concentrating on his duties as permanent secretary of the French Academy. As the result of his refusal of an operation (without which his doctors informed him he would not survive) for a painful bladder ailment he had had for years, d'Alembert died on 29 October 1783.

Bibliography

Primary Sources

Alembert, Jean Le Rond d'. Œuvres de d'Alembert. 5 vols, reprint of 1821–1822 Paris edition. Geneva, 1967.

——. Œuvres et correspondances inédites de d'Alembert. Edited by Charles Henry. Reprint. Geneva, 1967.

——. Preliminary Discourse to the Encyclopedia of Diderot. Edited by Walter E. Rex and Richard N. Schwab. Chicago, 1995.

——. Traité de dynamique. Sceaux, 1990.

Secondary Sources

Essar, Dennis F. The Language Theory, Epistemology, and Aesthetics of Jean Lerond d'Alembert. Oxford, 1976.

Grimsley, Ronald. Jean d'Alembert (1717–1783). Oxford, 1963.

Hankins, Thomas L. Jean d'Alembert: Science and the Enlightenment. Oxford, 1970.

Pappas, John N. Voltaire and D'Alembert. Bloomington, Ind., 1962.

—PATRICK RILEY, JR.

"d'Alembert" redirects here. For the lunar crater, see d'Alembert (crater).

Jean le Rond d'Alembert
Jean le Rond d'Alembert, pastel by Maurice Quentin de La Tour.
Born	16 November 1717 Paris
Died	29 October 1783
Nationality	French
Fields	Mathematics Mechanics Physics Philosophy
Known for	Fluid mechanics Encyclopédie

Jean le Rond d'Alembert (16 November 1717 – 29 October 1783) was a French mathematician, mechanician, physicist and philosopher. He was also co-editor with Denis Diderot of the Encyclopédie. D'Alembert's method for the wave equation is named after him.

Contents 1 Childhood 2 Studies and adult life 3 Career 4 Personal life 5 Death 6 Legacy 7 Fictional portrayal 8 Bibliography 9 See also 10 Notes 11 External links

Childhood

Born in Paris, d'Alembert was the illegitimate child of the writer Claudine Guérin de Tencin and the chevalier Louis-Camus Destouches, an artillery officer. Destouches was abroad at the time of d'Alembert's birth, and a couple of days after birth his mother left him on the steps of the Saint-Jean-le-Rond de Paris church. According to custom, he was named after the patron saint of the church. D'Alembert was placed in an orphanage for found children, but was soon adopted by the wife of a glazier. Destouches secretly paid for the education of Jean le Rond, but did not want his parentage officially recognised.

Studies and adult life

Classical mechanics

Newton's Second Law

History of ... Fundamental concepts Space · Time · Mass · Force Energy · Momentum Formulations Newtonian mechanics Lagrangian mechanics Hamiltonian mechanics Branches Statics Dynamics Kinematics Applied mechanics Celestial mechanics Continuum mechanics Statistical mechanics Scientists Isaac Newton · Jeremiah Horrocks · Leonhard Euler · Jean le Rond d'Alembert · Alexis Clairaut Joseph Louis Lagrange · Pierre-Simon Laplace · William Rowan Hamilton · Siméon-Denis Poisson

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D'Alembert first attended a private school. The chevalier Destouches left d'Alembert an annuity of 1200 livres on his death in 1726. Under the influence of the Destouches family, at the age of twelve D'Alembert entered the Jansenist Collège des Quatre-Nations (the institution was also known under the name "Collège Mazarin"). Here he studied philosophy, law, and the arts, graduating as bachelier in 1735. In his later life, D'Alembert scorned the Cartesian principles he had been taught by the Jansenists: "physical premotion, innate ideas and the vortices".

The Jansenists steered D'Alembert toward an ecclesiastical career, attempting to deter him from pursuits such as poetry and mathematics. Theology was, however, "rather unsubstantial fodder" for d'Alembert. He entered law school for two years, and was nominated avocat in 1738.

He was also interested in medicine and mathematics. Jean was first registered under the name Daremberg, but later changed it to d'Alembert. The name "d'Alembert" was proposed by Johann Heinrich Lambert for a suspected (but non-existent) moon of Venus.

Career

In July 1739 he made his first contribution to the field of mathematics, pointing out the errors he had detected in L'analyse démontrée (published 1708 by Charles René Reynaud) in a communication addressed to the Académie des Sciences. At the time L'analyse démontrée was a standard work, which d'Alembert himself had used to study the foundations of mathematics. D'Alembert was also a Latin scholar of some note and worked in the latter part of his life on a superb translation of Tacitus, from which he received wide praise including that of Denis Diderot.

In 1740, he submitted his second scientific work from the field of fluid mechanics Mémoire sur la réfraction des corps solides, which was recognized by Clairaut. In this work d'Alembert theoretically explained refraction.

In 1741, after several failed attempts, d'Alembert was elected into the Académie des Sciences. He was later elected to the Berlin Academy in 1746 ^[1]

When the Encyclopédie was organized in the late 1740s, d'Alembert was engaged as co-editor (for mathematics and science) with Diderot, and served until a series of crises temporarily interrupted the publication in 1757. He authored over a thousand articles for it, including the famous Preliminary Discourse. D'Alembert "abandoned the foundation of Materialism"^[2] when he "doubted whether there exists outside us anything corresponding to what we suppose we see."^[3] In this way, D'Alembert agreed with the Idealist Berkeley and anticipated the Transcendental idealism of Kant.

In 1752, he wrote about what is now called D'Alembert's paradox: that the drag on a body immersed in an inviscid, incompressible fluid is zero.

In 1754, d'Alembert was elected a member of the Académie française, of which he became Permanent Secretary on 9 April 1772.

Personal life

D'Alembert was a participant in several Parisian salons, particularly those of Marie Thérèse Rodet Geoffrin, of the marquise du Deffand and of Julie de Lespinasse. He met Denis Diderot at the salon of Julie de Lespinasse. d'Alembert became infatuated with Mlle de Lespinasse, and eventually took up residence with her.

Death

He suffered bad health for many years and his death was as the result of a bladder illness. As a known unbeliever, D'Alembert was buried in a common unmarked grave.

Legacy

In France, the fundamental theorem of algebra is known as the d'Alembert/Gauss theorem.

He also created his ratio test, a test to see if a series converges.

The D'Alembertian operator, which first arose in D'Alembert's analysis of vibrating strings, plays an important role in modern theoretical physics.

While he made great strides in mathematics and physics, d'Alembert is also famously known for incorrectly arguing in Croix ou Pile that the probability of a coin landing heads increased for every time that it came up tails. In gambling, the strategy of decreasing one's bet the more one wins and increasing one's bet the more one loses is therefore called the D'Alembert system, a type of martingale.

Fictional portrayal

Diderot portrayed D'Alembert in "Le reve de D'Alembert" ("D'Alembert's Dream"), written after the two men became estranged. It depicts D'Alembert ill in bed, conducting a debate on materialist philosophy in his sleep.

The Andrew Crumey novel "D'Alembert's Principle" (1996) takes its title from D'Alembert's principle in physics. Its first part describes D'Alembert's life and his infatuation with Julie de Lespinasse.

Bibliography

• Briggs, J. Morton (1970). "Jean le Rond d'Alembert". Dictionary of Scientific Biography. 1. New York: Charles Scribner's Sons. pp. 110-17. ISBN 0684101149. 
• Crépel, Pierre, 2005, "Traité de dynamique" in Grattan-Guinness, I., ed., Landmark Writings in Western Mathematics. Elsevier: 159-67.
• Grimsley, Ronald (1963) Jean d'Alembert. Oxford Univ. Press.

See also

• Liberalism
• Contributions to liberal theory
• Gambler's fallacy
• Wave equation
• Preliminary Discourse to the Encyclopedia of Diderot
• D'Alembert's principle
• d'Alembert's formula
• D'Alembert's paradox

Notes

1. ^ Hankins, T.L. (1990), Jean d'Alembert: Science and the Enlightenment, p. 26, http://books.google.co.uk/books?hl=en&lr=&id=gwjc3vGW9-MC&oi=fnd&pg=PP13&dq=Jean+D%27Alembert:+Science+and+the+Enlightenment&ots=baaB_HFr2g&sig=LBVdh1RukZzP8aI8UuF-CPuHM9M, retrieved 2009-10-27 
2. ^ Friedrich Albert Lange, History of Materialism and Critique of its Present Importance, "Kant and Materialism"
3. ^ Ibid.

External links

Wikimedia Commons has media related to: Jean le Rond d'Alembert

French Wikisource has original text related to this article: Jean le Rond d'Alembert

Wikisource has the text of the 1911 Encyclopædia Britannica article Alembert, Jean le Rond d'.

• D'Alembert's accusation of Euler's plagiarism at Convergence
• English translation of part of the Encyclopédie of Diderot and d'Alembert
• O'Connor, John J.; Robertson, Edmund F., "Jean le Rond d'Alembert", MacTutor History of Mathematics archive, http://www-history.mcs.st-andrews.ac.uk/Biographies/D'Alembert.html .
• An Account of the Destruction of the Jesuits in France by Jean Le Rond d' Alembert (1766)
• Select Eulogies of the Members of the French AcademyWith Notes by Jean Le Rond d' Alembert (1799)
• Correspondence with Frederick the Great
• The ARTFL Encyclopédie, provided by the ARTFL Project of the University of Chicago (articles in French, scans of 18th century print copies provided)
• The Encyclopedia of Diderot & d'Alembert Collaborative Translation Project, product of the Scholarly Publishing Office of the University of Michigan Library (an effort to translate the Encyclopédie into English)

Preceded by Jean-Baptiste Surian

Seat 25 Académie française 1754–1783

Succeeded by Marie-Gabriel-Florent-Auguste de Choiseul-Gouffier

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