Jean Le Rond d'Alembert

Early Life

Jean Le Rond d'Alembert was born in Paris in 1717. He was left on the steps of a church as a baby. A family took him in and cared for him.

Contributions to Science and Mathematics

D'Alembert became a famous mathematician, mechanician, physicist, philosopher, and music theorist. He helped Denis Diderot work on the Encyclopédie. This big book tried to collect all the knowledge of the time.

One of d'Alembert's big achievements was creating D'Alembert's formula. This formula helps solve problems about how waves move. It deals with the wave equation, which explains wave motion. Sometimes this equation is called d'Alembert's equation.

In France, an important math rule is named after him. It is called the fundamental theorem of algebra. This shows how much he helped math and science.

Early years

Jean Le Rond d'Alembert was born in Paris. His mother was a writer named Claudine Guérin de Tencin. His father was an artillery officer named Louis-Camus Destouches. Because his father was away often, his mother left him at the Saint-Jean-le-Rond de Paris church when he was very young. He was taken to an orphanage for foundling children. Later, his father made arrangements for him to live with a woman named Madame Rousseau. She cared for him for almost 50 years. His father helped pay for his education, but he never told Madame Rousseau that Jean was his son.

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. There he studied philosophy, law, and the arts. He later decided that the ideas he learned there, called "Cartesian" principles, didn’t match his own beliefs.

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 became 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 found mistakes in a famous math book and shared his ideas with the Académie des Sciences. He explained how light bends when it passes through clear materials, a process called refraction.

D'Alembert was elected to 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 became interested in music theory in 1749 when he reviewed a paper by Jean-Philippe Rameau. He liked Rameau's work and thought it matched his own scientific ideas. In 1752, d'Alembert wrote a book about Rameau's music theories, which helped many people learn about Rameau's ideas. But because d'Alembert was not a musician, he sometimes misunderstood Rameau's ideas.

D'Alembert also wrote about music in the Encyclopédie. He said that music could not copy reality as well as other arts. He thought that modern music had reached its highest point in his time because there were no ancient Greek models to follow. He praised Rameau for improving French music after Jean-Baptiste Lully.

Personal life

D'Alembert spent time in many Parisian salons. He often visited the salons led by Marie Thérèse Rodet Geoffrin, the marquise du Deffand, and Julie de Lespinasse. He cared deeply for Julie de Lespinasse and later lived with her.

Death

He had poor health for many years and died from an illness of the urinary bladder. Because he was known as an 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 thought 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 wrote a story called Le rêve de D'Alembert (D'Alembert's Dream). In this story, d'Alembert dreams about big ideas.

Another book, D'Alembert's Principle by Andrew Crumey, was published in 1996. The book uses a physics idea by d'Alembert and tells parts of his life.

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