André Marie Ampère

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 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.