André-Marie Ampère (20 January 1775 – 10 June 1836) was a French physicist and mathematician who is generally regarded as one of the main founders of the science of classical electromagnetism, which he referred to as “electrodynamics”. The SI unit of measurement of electric current, the ampere, is named after him.
He was born Jean-Jacques Ampère, a prosperous businessman, and Jeanne Antoinette Desutières-Sarcey Ampère during the height of the French Enlightenment. He spent his childhood and adolescence at the family property at Poleymieux-au-Mont-d’Or near Lyon. Jean-Jacques Ampère, a successful merchant, was an admirer of the philosophy of Jean-Jacques Rousseau, whose theories of education (as outlined in his treatise Émile) were the basis of Ampère’s education. Rousseau believed that young boys should avoid formal schooling and pursue instead an “education direct from nature.”
Ampère’s father actualized this ideal by allowing his son to educate himself within the walls of his well-stocked library. French Enlightenment masterpieces such as Georges-Louis Leclerc, comte de Buffon’s Histoire naturelle, générale et particulière (begun in 1749) andDenis Diderot and Jean le Rond d’Alembert’s Encyclopédie (volumes added between 1751 and 1772) thus became Ampère’s schoolmasters. The young Ampère, however, soon resumed his Latin lessons, which enabled him to master the works of Leonhard Euler and Daniel Bernoulli.
In addition, Ampère used his access to the latest mathematical books to begin teaching himself advanced mathematics at age 12. In later life Ampère claimed that he knew as much about mathematics and science when he was eighteen as ever he knew; but, as a polymath, his reading embraced history, travels, poetry, philosophy, and the natural sciences.
In 1796 Ampère met Julie Carron, and in 1799 they were married. André-Marie Ampère took his first regular job in 1799 as a mathematics teacher, which gave him the financial security to marry Carron and father his first child, Jean-Jacques (named after his father), the next year. (Jean-Jacques Ampère eventually achieved his own fame as a scholar of languages).
In 1802 Ampère was appointed a professor of physics and chemistry at the École Centrale in Bourg-en-Bresse, leaving his ailing wife and infant son in Lyon. He used his time in Bourg to research mathematics, producing Considérations sur la théorie mathématique de jeu (1802; “Considerations on the Mathematical Theory of Games”), a treatise on mathematical probability that he sent to the Paris Academy of Sciences in 1803.
Despite his lack of formal qualifications, Ampère was appointed a professor of mathematics at the school in 1809. As well as holding positions at this school until 1828, in 1819 and 1820 Ampère offered courses in philosophy and astronomy, respectively, at the University of Paris, and in 1824 he was elected to the prestigious chair in experimental physics at the Collège de France.
In September 1820, Ampère’s friend and eventual eulogist François Arago showed the members of the French Academy of Sciences the surprising discovery of Danish physicistHans Christian Ørsted that a magnetic needle is deflected by an adjacent electric current. Ampère began developing a mathematical and physical theory to understand the relationship between electricity and magnetism.
Furthering Ørsted’s experimental work, Ampère showed that two parallel wires carrying electric currents attract or repel each other, depending on whether the currents flow in the same or opposite directions, respectively – this laid the foundation of electrodynamics. He also applied mathematics in generalizing physical laws from these experimental results. The most important of these was the principle that came to be called Ampère’s law, which states that the mutual action of two lengths of current-carrying wire is proportional to their lengths and to the intensities of their currents.
Ampère also provided a physical understanding of the electromagnetic relationship, theorizing the existence of an “electrodynamic molecule” (the forerunner of the idea of theelectron) that served as the component element of both electricity and magnetism. Using this physical explanation of electromagnetic motion, Ampère developed a physical account of electromagnetic phenomena that was both empirically demonstrable and mathematically predictive.
In 1827 Ampère published his magnum opus, Mémoire sur la théorie mathématique des phénomènes électrodynamiques uniquement déduite de l’experience (Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience), the work that coined the name of his new science, electrodynamics, and became known ever after as its founding treatise.
In recognition of his contribution to the creation of modern electrical science, an international convention signed in 1881 established the ampere as a standard unit of electrical measurement, along with thecoulomb, volt, ohm, and watt, which are named, respectively, after Ampère’s contemporaries Charles-Augustin de Coulomb of France, Alessandro Volta of Italy, Georg Ohm ofGermany, and James Watt of Scotland. His name is one of the 72 names inscribed on the Eiffel Tower.