André-Marie Ampère (20 January 1775 – 10 June 1836), was a French physicist and mathematician who is generally credited as one of the main discoverers of electromagnetism. The SI unit of measurement of electric current, the ampere, is named after him.
In later life he used to claim that he knew as much about mathematics and science when he was eighteen as ever he knew; but, a polymath, his reading embraced nearly the whole round of knowledge—history, travels, poetry, philosophy and the natural sciences.
During the revolution his father stayed at Lyons expecting to be safer in the city. Nevertheless, after the revolutionaries had taken the city he fell a victim and was executed. This death was a great shock to Ampère.
In 1796 he met Julie Carron, the daughter of a blacksmith living near Lyon, and in 1799 they were married. From about 1796 Ampère gave private lessons at Lyon in mathematics, chemistry and languages; and in 1801 he removed to Bourg, as professor of physics and chemistry, leaving his ailing wife and infant son (Jean-Jacques Ampère) at Lyon. Her death, in July 1803, troubled Ampère for the rest of his life. Also in 1804, Ampère was appointed professor of mathematics at the lycée of Lyon.
Ampère used to say that "at eighteen years he found three culminating points in his life, his First Communion, the reading of Thomas's "Eulogy of Descartes", and the Taking of the Bastille... On the day of his wife's death he wrote two verses from the Psalms, and the prayer, 'O Lord, God of Mercy, unite me in Heaven with those whom you have permitted me to love on earth.' Serious doubts harassed him at times, and made him very unhappy. Then he would take refuge in the reading of the Bible and the Fathers of the Church.
Ampère's fame mainly rests on the fact that he rendered to science in establishing the relations between electricity and magnetism, and in developing the science of electromagnetism, or, as he called it, electrodynamics. On 11 September 1820 he heard of H. C. Ørsted's discovery that a magnetic needle is acted on by a voltaic current. Only a week later, on 18 September, he presented a paper to the Academy containing a far more complete exposition of that and kindred phenomena. On the same day Ampère also demonstrated before the Academy that parallel wires carrying currents attract or repel each other (depending on whether currents are in the same or in opposite directions). This laid the foundation of the science of electrodynamics.
The field of electromagnetism thus opened up, he explored with characteristic industry and care, and developed a mathematical theory which not only explained the electromagnetic phenomena already observed, but also predicted many new ones.
Ampère's final work, published posthumously, was Essai sur la philosophie des sciences, ou exposition analytique d'une classification naturelle de toutes les connaissances humaines ("Essay on the philosophy of science or analytical exposition on the natural classification of human knowledge").
Ampère died at Marseille and is buried in the Cimetière de Montmartre, Paris. The great amiability and childlike simplicity of his character are well brought out in his Journal et correspondence (Paris, 1872).