Jean-Baptiste le Rond d'Alembert (; ; 16 November 1717 – 29 October 1783) was a French mathematician,
mechanician,
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe.
Physicists generally are interested in the root or ultimate cau ...
, philosopher, and
music theorist
Music theory is the study of the practices and possibilities of music. ''The Oxford Companion to Music'' describes three interrelated uses of the term "music theory". The first is the " rudiments", that are needed to understand music notation ( ...
. Until 1759 he was, together with
Denis Diderot
Denis Diderot (; ; 5 October 171331 July 1784) was a French philosopher, art critic, and writer, best known for serving as co-founder, chief editor, and contributor to the '' Encyclopédie'' along with Jean le Rond d'Alembert. He was a promi ...
, a co-editor of the ''
Encyclopédie''.
D'Alembert's formula for obtaining solutions to the
wave equation
The (two-way) wave equation is a second-order linear partial differential equation for the description of waves or standing wave fields — as they occur in classical physics — such as mechanical waves (e.g. water waves, sound waves and ...
is named after him. The wave equation is sometimes referred to as
d'Alembert's equation, and the
fundamental theorem of algebra is named after d'Alembert in French.
Early years
Born in Paris, d'Alembert was the
natural son of the writer
Claudine Guérin de Tencin
Claudine Alexandrine Guérin de Tencin, Baroness of Saint-Martin-de-Ré (27 April 1682 – 4 December 1749) was a French salonist and author. She was the mother of Jean le Rond d'Alembert, who later became a prominent mathematician, ''philosophe' ...
and the chevalier
Louis-Camus Destouches, an
artillery
Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during si ...
officer. Destouches was abroad at the time of d'Alembert's birth. Days after birth his mother left him on the steps of the church. According to custom, he was named after the
patron saint
A patron saint, patroness saint, patron hallow or heavenly protector is a saint who in Catholicism, Anglicanism, or Eastern Orthodoxy is regarded as the heavenly advocate of a nation, place, craft, activity, class, clan, family, or perso ...
of the church. D'Alembert was placed in an
orphanage
An orphanage is a residential institution, total institution or group home, devoted to the care of orphans and children who, for various reasons, cannot be cared for by their biological families. The parents may be deceased, absent, or a ...
for
foundling children, but his father found him and placed him with the wife of a
glazier, Madame Rousseau, with whom he lived for nearly 50 years. She gave him little encouragement. When he told her of some discovery he had made or something he had written she generally replied,
Destouches secretly paid for the education of Jean le Rond, but did not want his
paternity officially recognised.
Studies and adult life
D'Alembert first attended a private school. The chevalier Destouches left d'Alembert an
annuity of 1200
livres
The (; ; abbreviation: ₶.) was one of numerous currencies used in medieval France, and a unit of account (i.e., a monetary unit used in accounting) used in Early Modern France.
The 1262 monetary reform established the as 20 , or 80.88 g ...
on his death in 1726. Under the influence of the Destouches family, at the age of 12 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 ''
baccalauréat en arts'' in 1735.
In his later life, d'Alembert scorned the
Cartesian principles he had been taught by the
Jansenists: "physical promotion, innate ideas and the vortices". The Jansenists steered d'Alembert toward an