Jean Le Rond d'Alembert

Jean Le Rond d'Alembert was a French mathematician, mechanician, physicist, philosopher, and music theorist who lived from 1717 to 1783. He made important contributions to many areas of science and mathematics. One of his famous achievements was working on the Encyclopédie with Denis Diderot until 1759. This was a big book that tried to collect all the knowledge of the time.

D'Alembert is also well-known for creating a special way to find answers to problems involving waves, called D'Alembert's formula. This formula helps solve the wave equation, which describes how waves move. Sometimes, this equation is called d'Alembert's equation. In France, the fundamental theorem of algebra is also named after him, showing his wide impact on math and science.

Early years

Jean Le Rond d'Alembert was born in Paris to the writer Claudine Guérin de Tencin and an artillery officer named Louis-Camus Destouches. Because his father was away, his mother left him at the Saint-Jean-le-Rond de Paris church shortly after he was born. He was then placed in an orphanage for foundling children. Later, his father arranged for him to live with a woman named Madame Rousseau, who cared for him for nearly 50 years. Although she didn’t encourage his interests, his father secretly helped pay for his education without admitting he was his parent.

Studies and adult life

Jean Le Rond d'Alembert first went to a private school. When he was 12, he joined the Jansenist Collège des Quatre-Nations, where he studied philosophy, law, and the arts. He later decided that the ideas he learned there, called "Cartesian" principles, didn’t quite fit with what he believed.

Though some tried to guide him toward a career in the church, d'Alembert was more interested in subjects like mathematics. He studied law for a short time and was named an avocat in 1738. Later, a king named Frederick the Great of Prussia wanted to name a moon after him, but d'Alembert said no.

Career

Jean Le Rond d'Alembert made many important contributions to science and mathematics. In 1739, he pointed out mistakes in a famous math book and shared his ideas with the Académie des Sciences. He later explained how light bends through clear materials, a process called refraction.

D'Alembert was elected to several important science groups, including the Berlin Academy and the Fellow of the Royal Society. He wrote a well-known book about how things move and worked with Denis Diderot to help create the Encyclopédie, writing many articles about science and math. Later, he joined the Académie Française and became its Permanent Secretary in 1772.

Music theories

D'Alembert first became interested in music theory in 1749 when he reviewed a paper by Jean-Philippe Rameau. He praised Rameau's work and saw it as supporting his own scientific ideas. In 1752, d'Alembert wrote a book about Rameau's music theories, helping to make Rameau's ideas more well-known. However, because d'Alembert was not a musician, he sometimes misunderstood Rameau's ideas.

D'Alembert also wrote about music in the Encyclopédie, saying that music had not been able to copy reality as well as other arts. He believed that modern music had reached its peak in his time because there were no ancient Greek models to follow. He praised Rameau for advancing French music after Jean-Baptiste Lully.

Personal life

D'Alembert spent time in several Parisian salons, especially those led by Marie Thérèse Rodet Geoffrin, the marquise du Deffand, and Julie de Lespinasse. He developed strong feelings for Julie de Lespinasse and eventually lived with her.

Death

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

Legacy

Jean Le Rond d'Alembert made many important contributions to mathematics and physics. In France, a key math rule is sometimes called the d'Alembert/Gauss theorem. He also developed a useful method called the ratio test to study number sequences. Additionally, a special math tool he created, called the d'Alembert operator, is important in modern physics.

Though he was a great thinker, d'Alembert once made a mistake in a book called Croix ou Pile. He wrongly claimed that the chance of a coin landing heads gets bigger each time it lands tails. Because of this, a betting strategy is named after him, called the d'Alembert system. Long ago, an island in South Australia, near Spencer Gulf, was named Ile d'Alembert by a French explorer, but today it is usually called Lipson Island. The island is a protected area for birds.

Fictional portrayal

Diderot included d'Alembert in a story called Le rêve de D'Alembert (D'Alembert's Dream), written after he and d'Alembert had a falling out. In this story, d'Alembert is shown lying in bed and having a dream debate about important ideas.

Another book named D'Alembert's Principle by Andrew Crumey came out in 1996. The book uses the name from a physics idea by d'Alembert, and it tells parts of d'Alembert's life, including his strong feelings for Julie de Lespinasse.

List of works

Jean Le Rond d'Alembert wrote many important books and papers. Some of his well-known works include:

• Traité de dynamique
• Recherches sur differens points importans du systeme du monde
• Preliminary Discourse to the Encyclopedia of Diderot
• _Traité de l'équilibre et du mouvement des fluides
• _Réflexions sur la cause générale des vents
• Éléments de musique, théorique et pratique
• _Encyclopédie ou dictionnaire raisonné des sciences, des arts et des métiers