Jean Le Rond d’Alembert
French mathematician and philosopher
born , Nov. 17, 1717, Paris, France
died Oct. 29, 1783, Paris
Main
French mathematician, philosopher, and writer, who achieved
fame as a mathematician and scientist before acquiring a
considerable reputation as a contributor to and editor of
the famous Encyclopédie.
Early life
The illegitimate son of a famous hostess, Mme de Tencin, and
one of her lovers, the chevalier Destouches-Canon,
d’Alembert was abandoned on the steps of the Parisian church
of Saint-Jean-le-Rond, from which he derived his Christian
name. Although Mme de Tencin never recognized her son,
Destouches eventually sought out the child and entrusted him
to a glazier’s wife, whom d’Alembert always treated as his
mother. Through his father’s influence, he was admitted to a
prestigious Jansenist school, enrolling first as Jean-Baptiste
Daremberg and subsequently changing his name, perhaps for
reasons of euphony, to d’Alembert. Although Destouches never
disclosed his identity as father of the child, he left his
son an annuity of 1,200 livres. D’Alembert’s teachers at
first hoped to train him for theology, being perhaps
encouraged by a commentary he wrote on St. Paul’s Letter to
the Romans, but they inspired in him only a lifelong
aversion to the subject. He spent two years studying law and
became an advocate in 1738, although he never practiced.
After taking up medicine for a year, he finally devoted
himself to mathematics—“the only occupation,” he said later,
“which really interested me.” Apart from some private
lessons, d’Alembert was almost entirely self-taught.
Mathematics
In 1739 he read his first paper to the Academy of Sciences,
of which he became a member in 1741. In 1743, at the age of
26, he published his important Traité de dynamique, a
fundamental treatise on dynamics containing the famous
“d’Alembert’s principle,” which states that Newton’s third
law of motion (for every action there is an equal and
opposite reaction) is true for bodies that are free to move
as well as for bodies rigidly fixed. Other mathematical
works followed very rapidly; in 1744 he applied his
principle to the theory of equilibrium and motion of fluids,
in his Traité de l’équilibre et du mouvement des fluides.
This discovery was followed by the development of partial
differential equations, a branch of the theory of calculus,
the first papers on which were published in his Réflexions
sur la cause générale des vents (1747). It won him a prize
at the Berlin Academy, to which he was elected the same
year. In 1747 he applied his new calculus to the problem of
vibrating strings, in his Recherches sur les cordes
vibrantes; in 1749 he furnished a method of applying his
principles to the motion of any body of a given shape; and
in 1749 he found an explanation of the precession of the
equinoxes (a gradual change in the position of the Earth’s
orbit), determined its characteristics, and explained the
phenomenon of the nutation (nodding) of the Earth’s axis, in
Recherches sur la précession des équinoxes et sur la
nutation de l’axe de la terre. In 1752 he published Essai
d’une nouvelle théorie de la résistance des fluides, an
essay containing various original ideas and new
observations. In it he considered air as an incompressible
elastic fluid composed of small particles and, carrying over
from the principles of solid body mechanics the view that
resistance is related to loss of momentum on impact of
moving bodies, he produced the surprising result that the
resistance of the particles was zero. D’Alembert was himself
dissatisfied with the result; the conclusion is known as
“d’Alembert’s paradox” and is not accepted by modern
physicists. In the Memoirs of the Berlin Academy he
published findings of his research on integral
calculus—which devises relationships of variables by means
of rates of change of their numerical value—a branch of
mathematical science that is greatly indebted to him. In his
Recherches sur différents points importants du système du
monde (1754–56) he perfected the solution of the problem of
the perturbations (variations of orbit) of the planets that
he had presented to the academy some years before. From 1761
to 1780 he published eight volumes of his Opuscules
mathématiques.
The Encyclopédie
Meanwhile, d’Alembert began an active social life and
frequented well-known salons, where he acquired a
considerable reputation as a witty conversationalist and
mimic. Like his fellow Philosophes—those thinkers, writers,
and scientists who believed in the sovereignty of reason and
nature (as opposed to authority and revelation) and rebelled
against old dogmas and institutions—he turned to the
improvement of society. A rationalist thinker in the
free-thinking tradition, he opposed religion and stood for
tolerance and free discussion; in politics the Philosophes
sought a liberal monarchy with an “enlightened” king who
would supplant the old aristocracy with a new, intellectual
aristocracy. Believing in man’s need to rely on his own
powers, they promulgated a new social morality to replace
Christian ethics. Science, the only real source of
knowledge, had to be popularized for the benefit of the
people, and it was in this tradition that he became
associated with the Encyclopédie about 1746. When the
original idea of a translation into French of Ephraim
Chambers’ English Cyclopædia was replaced by that of a new
work under the general editorship of the Philosophe Denis
Diderot, d’Alembert was made editor of the mathematical and
scientific articles. In fact, he not only helped with the
general editorship and contributed articles on other
subjects but also tried to secure support for the enterprise
in influential circles. He wrote the Discours préliminaire
that introduced the first volume of the work in 1751. This
was a remarkable attempt to present a unified view of
contemporary knowledge, tracing the development and
interrelationship of its various branches and showing how
they formed coherent parts of a single structure; the second
section of the Discours was devoted to the intellectual
history of Europe from the time of the Renaissance. In 1752
d’Alembert wrote a preface to Volume III, which was a
vigorous rejoinder to the Encyclopédie’s critics, while an
Éloge de Montesquieu, which served as the preface to Volume
V (1755), skillfully but somewhat disingenuously presented
Montesquieu as one of the Encyclopédie’s supporters.
Montesquieu had, in fact, refused an invitation to write the
articles “Democracy” and “Despotism,” and the promised
article on “Taste” remained unfinished at his death in 1755.
In 1756 d’Alembert went to stay with Voltaire at Geneva,
where he also collected information for an Encyclopédie
article, “Genève,” which praised the doctrines and practices
of the Genevan pastors. When it appeared in 1757, it aroused
angry protests in Geneva because it affirmed that many of
the ministers no longer believed in Christ’s divinity and
also advocated (probably at Voltaire’s instigation) the
establishment of a theatre. This article prompted Rousseau,
who had contributed the articles on music to the
Encyclopédie, to argue in his Lettre à d’Alembert sur les
spectacles (1758) that the theatre is invariably a
corrupting influence. D’Alembert himself replied with an
incisive but not unfriendly Lettre à J.-J. Rousseau, citoyen
de Genève. Gradually discouraged by the growing difficulties
of the enterprise, d’Alembert gave up his share of the
editorship at the beginning of 1758, thereafter limiting his
commitment to the production of mathematical and scientific
articles.
Later literary, scientific, and philosophical work
His earlier literary and philosophical activity, however,
led to the publication of his Mélanges de littérature,
d’histoire et de philosophie (1753). This work contained the
impressive Essai sur les gens de lettres, which exhorted
writers to pursue “liberty, truth and poverty” and also
urged aristocratic patrons to respect the talents and
independence of such writers.
Largely as a result of the persistent campaigning of Mme
du Deffand, a prominent hostess to writers and scientists,
d’Alembert was elected to the French Academy in 1754; he
proved himself to be a zealous member, working hard to
enhance the dignity of the institution in the eyes of the
public and striving steadfastly for the election of members
sympathetic to the cause of the Philosophes. His personal
position became even more influential in 1772 when he was
made permanent secretary. One of his functions was the
continuation of the Histoire des membres de l’Académie; this
involved writing the biographies of all the members who had
died between 1700 and 1772. He paid tribute to his
predecessors by means of Éloges that were delivered at
public sessions of the academy. Though of limited literary
value, they throw interesting light on his attitude toward
many contemporary problems and also reveal his desire to
establish a link between the Academy and the public.
From 1752 onward, Frederick II of Prussia repeatedly
tried to persuade d’Alembert to become president of the
Berlin Academy, but the philosopher contented himself with a
brief visit to the King at the Rhine village of Wesel in
1755 and a longer stay at Potsdam in 1763. For many years he
gave the King advice on the running of the academy and the
appointment of new members. In 1762 another monarch, the
empress Catherine II of Russia, invited d’Alembert to become
tutor to her son, the grand duke Paul; this offer also was
refused. Apart from fearing the harmful effects of foreign
residence upon his health and personal position, d’Alembert
did not wish to be separated from the intellectual life of
Paris.
Although as a skeptic, d’Alembert willingly supported the
Philosophes’ hostility to Christianity, he was too cautious
to become openly aggressive. The expulsion of the Jesuits
from France, however, prompted him to publish “by a
disinterested author,” at first anonymously, and then in his
own name, Sur la destruction des Jésuites en France (1765;
An Account of the Destruction of the Jesuits in France,
1766). He there tried to show that the Jesuits, in spite of
their qualities as scholars and educators, had destroyed
themselves through their inordinate love of power.
During these years d’Alembert’s interests included
musical theory. His Éléments de musique of 1752 was an
attempt to expound the principles of the composer
Jean-Philippe Rameau (1683–1764), who had consolidated
contemporary musical development into a harmonic system that
dominated Western music until about 1900. In 1754 d’Alembert
published an essay expressing his thoughts on music in
general—and French music in particular—entitled Réflexions
sur la musique en général et sur la musique française en
particulier. He also published in his mathematical opuscules
treatises on acoustics, the physics of sound, and he
contributed several articles on music to the Encyclopédie.
In 1765 a serious illness compelled him to leave his
foster-mother’s house, and he eventually went to live in the
house of Julie de Lespinasse, with whom he fell in love. He
was the leading intellectual figure in her salon, which
became an important recruiting centre for the French
Academy. Although they may have been intimate for a short
time, d’Alembert soon had to be satisfied with the role of
steadfast friend. He discovered the extent of her passionate
involvement with other men only after Julie’s death in 1776.
He transferred his home to an apartment at the Louvre—to
which he was entitled as secretary to the Academy—where he
died.
Assessment
Posterity has not confirmed the judgment of those
contemporaries who placed d’Alembert’s reputation next to
Voltaire’s. In spite of his original contributions to the
mathematical sciences, intellectual timidity prevented his
literary and philosophical work from attaining true
greatness. Nevertheless, his scientific background enabled
him to elaborate a philosophy of science that, inspired by
the rationalist ideal of the ultimate unity of all
knowledge, established “principles” making possible the
interconnection of the various branches of science.
Moreover, d’Alembert was a typical 18th-century Philosophe,
for in both his life and his work he tried to invest the
name with dignity and serious meaning. In his personal life
he was simple and frugal, never seeking wealth and
dispensing charity whenever possible, always watchful of his
integrity and independence, and constantly using his
influence, both at home and abroad, to encourage the advance
of “enlightenment.”
Ronald Grimsley
