unit of electric current

After the French physicist André-Marie Ampère (Poleymieux-au-Mont-d'Or 1775 Marseille 1836).

What would electricity be without magnetism? Motors and transformers, the entire power current, but also the telephone and the radio are examples of how electric currents generate magnetic fields and vice versa. The Danish physicist Hans Christian Oersted (1777-1851) noticed in the year 1820 during a lecture about his experiments that a compass needle – a thin magnet – deflected near a wire through which current ran. That same year, scientists in Paris set to work on the basis of that fact. The experiments were repeated systematically and laid the foundations of the laws governing the technical use of electricity. The central figure was André-Marie Ampère.

Ampère's father was a merchant of silk products and a municipal councilor in Lyon. Young André-Marie was privately educated and turned out to be something of a child prodigy.

Very young he processed a multi-volume encyclopaedia, at the age of twelve he mastered the complete higher mathematics of the time, a purely academic matter, and at the age of thirteen, the annals state, he wrote a treatise on conic sections.

In 1789, the French Revolution broke out. In 1792, his beloved sister Antoinette died, aged twenty. In 1793 a counter-revolutionary uprising arose in Lyon, to which father Ampère joined. Like so many Frenchmen, he had first supported the revolution and, when it degenerated, he rebelled.

The revolutionaries captured Lyon and Father Ampère was guillotined on November 23.

Ampere was eighteen at the time. According to some sources it took him a year to regain his speech, according to others he sank into a deep depression for many years, from which he was only freed by reading Rousseau.

His studies covered botany, metaphysics and psychology before finally moving on to mathematics and physics. He married Julie Carton in 1799, who bore him a son but died of cancer in 1803, another tragedy from which he would never truly recover.

He fled into science and would remain for the rest of his life a withdrawn man, the type of absent-minded professor with little interest in the world around him.

An unhappy second marriage in 1806 led to a divorce two years later.
Napoleon appointed him in 1809 to the famous Ecole Polytechnique in Paris for the chair of mechanics. From 1824 he taught physics at the Collège de France and even philosophy at the faculty of arts. In 1814, the Academy of Sciences elected him a member of the mathematics department.

Barely a few weeks after Oersted's discovery, he demonstrated for this academy from September 1820 a number of connections between electricity and magnetism, two natural phenomena that had until then been studied separately. He immediately showed how parallel wires carrying current in the same direction attract each other and how they repel each other when the current flows in the opposite direction. He proved that two closed circuits interact with each other, thereby cranking up the whole of electrodynamics, as it were. Two years later, Faraday would develop induction on the basis of this pioneering work, the generation of electricity using magnetic fields. In 1821, Ampère explained magnetism with his theory of electric particle currents, a theory that did not gain acceptance until a hundred years later.
Ampère was shy and timid and so distracted that one day he simply forgot about Napoleon's invitation to dinner. For once, the Emperor was willing to forgive him. He died on 10 June 1836 in Marseilles while on duty as a school inspector.

His death hardly attracted attention.

A biographer: 'From the age of seventeen Ampere had known so much misery that his death was a release from this vale of tears.

That he did so much scientific groundbreaking work in those circumstances is simply astonishing.' Earlier he had said that he would have liked to see the text 'Tandem felix' (happy at last) on his grave.

In the year 1881, an international congress in Paris decided to name the unit of current after him. The ampere became that strength of current which in a solution of silver nitrate separates 1.118 milligrams of silver in one second.

Ampère's son Jean-Jacques-Antoine (1800-1864), a well-known man of letters and historian, was more of a man of the world than his father. He was a friend and admirer of Madame Récamier, the Parisian salon lady after whom the Récamier is named.

Father and son Ampère are buried together in the cemetery of Montmartre.

> (see also farad and récamier)