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André-Marie Ampère
1775–1836 · Physicist and Mathematician
A French mathematician and physicist who, inspired by a chance discovery, founded the science of electrodynamics in a single astonishing week of work.
Why is this scientist famous?
Foundational work on the relationship between electricity and magnetism. The SI unit of electric current, the ampere or amp (A), is named after him.
André-Marie's story
A Childhood Marked by Revolution
André-Marie Ampère was born in Lyon, France, during the reign of Louis XVI. His father was a prosperous merchant and local official who educated André-Marie at home using the Encyclopédie and the works of classical authors. The boy was a prodigy who began exploring advanced mathematical texts around age 13 and also received some help learning calculus from a teacher. But his life was shattered by the French Revolution. His father was arrested and executed on the guillotine in 1793 when André-Marie was 18. The trauma devastated him, and he experienced more than a year of severe distress and withdrawal before gradually returning to his studies. He emerged from this period with a deep philosophical and religious sensibility that would stay with him for life.
Rise Through Mathematics
Ampère gradually rebuilt his life through science and mathematics. He became a schoolteacher in Bourg and then Lyon, and in 1804 he was appointed an analysis tutor (répétiteur) at the École Polytechnique in Paris. In 1807, he was appointed substitute professor of mechanics and analysis there. He contributed to mathematics, chemistry and philosophy, and continued his scientific work despite personal difficulties, including the early death of his first wife.
The Week That Changed Physics
On 4 and 11 September 1820, François Arago reported to the French Academy of Sciences the Danish physicist Hans Christian Ørsted's finding that an electric current could deflect a compass needle. Ampère responded with experiments of his own. He presented initial results to the Academy on 18 September and reported the interaction between two electric currents on 25 September. He continued developing the experiments and their mathematical explanation during the months and years that followed, helping establish the field of electrodynamics. In particular, parallel current-carrying wires can attract or repel one another depending on the direction of the currents.
Electrodynamics
Ampère continued to develop his new science over the following years. He published his magnum opus, 'Memoir on the Mathematical Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience', in 1827. In it he presented the mathematical framework that describes the force between current-carrying wires — now known as Ampère's Law. He argued that magnetism itself was caused by circulating electric currents, a remarkably modern insight that anticipated the discovery of electrons by nearly a century. His work unified electricity and magnetism into a single framework and laid the groundwork that James Clerk Maxwell would later build upon to create the full theory of electromagnetism.
A Life of Contradictions
Despite his towering scientific achievements, Ampère's personal life was marked by tragedy and difficulty. His first wife died young. His daughter married a man Ampère despised, causing a painful family rupture. His son, Jean-Jacques, became a famous historian and writer but their relationship was strained. Ampère was deeply religious and philosophical, spending as much time on metaphysics and theology as on physics. He was known for his absent-mindedness — he once wrote a letter completely in blank because he had forgotten to dip his pen in ink. Yet behind the distracted exterior was one of the most powerful minds in European science.
Legacy
Ampère died in Marseille in 1836 at the age of 61. The ampere (A), now the SI base unit of electric current, is named in his honour. His research into interactions between electrical currents helped establish the foundations of electrodynamics. Electromagnetism now underpins technologies including electric motors, generators and telecommunications.
What did they discover?
Ampère's Law
Derived the mathematical law describing the force between two parallel current-carrying wires. This was the first quantitative law of electromagnetism and laid the foundation for James Clerk Maxwell's later unified theory. The law is still used today in the design of electric motors, generators, and transformers.
Electrodynamics
Founded the entirely new science of electrodynamics in October 1820, showing that electric currents produce magnetic forces and that magnetism itself is caused by circulating electric currents — an insight that anticipated the discovery of the electron by nearly a century.
The Solenoid Concept
Ampère proposed that a helical coil of wire carrying a current would behave like a magnet, a device he helped conceptualise. This principle underlies the electromagnet, which is used in countless devices from doorbells to MRI machines.
The Ampere (SI Unit)
The ampere (A), the SI unit of electric current, was named in his honour in 1881. One ampere is the current that, flowing through two parallel wires one metre apart, produces a force of 2 × 10⁻⁷ newtons per metre of length — a definition directly based on Ampère's own experiments.
Amazing facts
After Arago introduced Ørsted's results in September 1820, Ampère rapidly devised new experiments and reported the interaction between electric currents to the Academy on 25 September.
His father was executed by guillotine during the French Revolution when André-Marie was 18, leaving him traumatised and silent for a year.
He was so absent-minded that he once wrote an entire letter in blank — he had forgotten to dip his pen in ink.
The ampere, the SI unit of electric current used to rate every electrical appliance on Earth, was named in his honour in 1881.
Ampère argued that magnetism was caused by circulating electric currents — a theory that anticipated the discovery of electrons by nearly a century.
He was a polymath who made contributions to mathematics, chemistry, philosophy, and theology, not just physics.
He coined the term 'electrodynamics' himself to describe the new science he had created.
Timeline
Born in Lyon, France
His father was executed during the French Revolution
Appointed analysis tutor (répétiteur) at the École Polytechnique in Paris
Heard reports of Ørsted's findings and presented early experiments on electrical currents in September
Announced the mutual action of two electric currents to the Academy on 25 September
Appointed professor of physics at the Collège de France
Published his magnum opus on the mathematical theory of electrodynamics
Died in Marseille, aged 61
Awards & honours
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