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André-Marie Ampère, (b. Jan. 10, 1775, d. June 10, 1836), was a French physicist who laid the foundations for the science of electrodynamics through his demonstration that electric currents produce magnetic fields, and through his subsequent investigation into the relationship between these two phenomena.

The son of a well-to-do merchant, Ampère educated himself through diligent reading in the family library. He survived the French Revolution to become a science teacher, first in Lyons and then in Bourg. He later took a post at the Ecole Polytechnique, and in 1808 became inspector general of the university system in Paris.

Beginning in 1824, he also taught physics at the College de France and philosophy at the Faculte des Lettres, pursuing diverse scientific interests in the midst of personal tragedy. He was greatly affected by his father's execution by guillotine during the Revolution and, after his first wife's early death, had a catastrophic second marriage.

Ampère's most notable achievements were his independent determination (1814) of Avogadro's law and his work from 1820 to 1827 based on Hans Christian Ørsted's discovery, announced in 1820, that a magnetic needle moves in the vicinity of an electric current. Ampère succeeded in explaining the latter phenomenon by assuming that an electric current is capable of exciting a magnetic field.

He further demonstrated that the direction of the magnetic field is determined by the direction of the current. He developed a quantitative relationship for the strength of a magnetic field in relation to an electric current (Ampère's theorem) and propounded a theory as to how iron becomes magnetized. Ampere also devised a rule governing the mutual interaction of current-carrying wires (Ampère's law) and produced a definition of the unit of measurement of current flow, now known as the Ampère.

Source: The New Grolier Multimedia Encyclopedia

André Ampère was a child prodigy and it is claimed he had mastered all known mathematics by the age of twelve years. In 1801 he was appointed professor of physics and chemistry at Bourg. Appointed professor of mathematics at the École Polytechnique in 1809 he held post there until 1828. He also was appointed to a chair at Université de France in 1826 which he held until his death.

Ampère worked on electromagnetism and analysis. He also made contributions to line geometry extending ideas of Binet.

In the early 1820's, Ampère attempted to give a combined theory of electricity and magnetism after hearing about experimental results by the Danish physicist Hans Christian Ørsted. Ampère formulated a circuit force law and treated magnetism by postulating small closed circuits inside the magnetised substance.

It is worth commenting on how quickly Ampère produced this theory, the inspiration striking him immediately he heard of Orsted's experimental results and he had written a paper giving a theoretical explanation within one week. Ampère's theory became fundamental for 19th century developments in electricity and magnetism.

Before Ampère nobody had any way of measuring the flow of electricity. Ampère built an instrument to measure the flow using a free-moving needle. It was an early version of the instrument later called the galvanometer.

Ampère's most important publication is Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience (1827).

Sources:

Dictionary of Scientific Biography

Biography in Encyclopaedia Britannica

L de Launay, Le grand Ampère (Paris, 1925)

C Blondel, A-M. Ampère et la creation de l'electrodynamique (1820-1827) (Paris, 1982)

J R Hofmann, André-Marie Ampère (Oxford, 1995)

L P Williams, André-Marie Ampère, Scientific American 260 (1989), 72-79

C A Valson, La vie et les travaux d'André-Marie Ampère (Lyon, 1886)

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