André-Marie Ampère

By Emeka Obi

When news reached Paris that a Danish physicist had made a compass needle move with an electric current, André-Marie Ampère — who had never worked on electricity — rebuilt the entire phenomenon in seven days and founded a new science.

Ampère was born in Lyon in 1775, a prodigy raised on Rousseau's Émile who taught himself mathematics from encyclopedia articles and was reading Euler's works by thirteen. His life was shadowed by the Revolution: his father was guillotined in 1793, and Ampère spent a year in near-catatonic grief. He recovered, became a professor, and by 1820 was the leading mathematical physicist of France — when Ørsted's discovery arrived that September.

What followed was one of the most intense weeks in science. Ampère showed that parallel currents attract when flowing the same way and repel when opposed; that a current-carrying coil behaves exactly like a magnet; that the force between currents follows precise mathematical laws. Within months he presented the Mémoire that founded electrodynamics: he proposed that magnetism itself is nothing but electricity in motion — that every magnet contains tiny molecular currents. This was the decisive break from the idea of separate magnetic fluids. His force law, and later Ampère's circuital law relating magnetic fields to the currents that produce them, gave electricity and magnetism a common mathematical language.

He was famously distracted — the absent-minded professor is practically his invention — yet his work on partial differential equations and the calculus of variations placed him among the great analysts of the age. His personal life was marked by tragedy, including the death of his wife. He died in Marseille in 1836, still working. The ampere, the unit of electric current, is his name: fitting, since every current measured anywhere in the world is measured in the unit of the man who first showed currents and magnets were the same thing.

Impact on civilization

Ampère founded electrodynamics — the science that electricity and magnetism are one phenomenon. His laws let engineers calculate the forces in motors, generators, and every electromagnetic device; his molecular-current hypothesis became the modern theory of magnetism, and his name is stamped on every current measured anywhere. Maxwell's equations are built on Ampère's law. The electrical age — power grids, electronics, telecommunications — is erected on the mathematics Ampère produced in a single feverish autumn, and every electric motor spinning on earth still obeys the force law he wrote down in 1820.