Arago goes all out for science

On September 25, 1820, French physicist Francois Arago announced his discovery of an occurrence of electromagnetism. This was just one of Arago’s many contributions as he spent a lifetime for the progress of science. A.S.Ganesh tells you more about the life of Arago…

It isn’t often that we come across a person who contributes significantly to a number of different fields. Such polymaths – individuals whose knowledge encompasses a wide range of subjects – have always been rare. Frenchman Dominique Francois Jean Arago was one such person in this world, as he donned the hat of a physicist, mathematician, astronomer, and politician in an eventful life.

Born in 1786 in Estagel, Roussillon, France, Arago was one of 11 children. Educated at the Municipal College of Perpignan, Arago was drawn towards mathematics from a young age. He was admitted to the Ecole Polytechnique in Paris, where he succeeded French mathematician Gaspard Monge as the chair of Analytic Geometry at the young age of 23.

He made his first major contributions to science in the decade that followed. Working with French engineer Augustin-Jean Fresnel, Arago was able to show that while two rays polarised in a plane can interfere with each other, two beams of light polarised perpendicular to each other cannot interfere with each other. This research led to the discovery of the laws of light polarisation.

In 1820, Arago briefly interrupted his optical work to significantly expand on electromagnetic theories. Having been invited to Geneva to witness the experiments of Danish physicist Hans Christian Oersted linking electricity to magnetism, Arago was instantly converted and developed a huge interest in the subject.

Apart from repeating the Geneva experiments at the Paris Academy, Arago also experimented on his own. He was able to demonstrate that by passing an electric current through a cylindrical spiral of wire, it could be made to behave like a magnet. The temporary magnetisation allowed it to attract iron filings, which then fell off when the current ceased. He announced this occurrence of electromagnetism on September 25, 1820.

Soon after, Arago discovered the principle of the production of magnetism by rotation of a nonmagnetic conductor. He was able to show that the rotation of a nonmagnetic metallic substance like copper created a magnetic effect as it produced rotation in a magnetic needle suspended over it. It was another decade before English scientist Michael Faraday explained these using his theory of electromagnetic induction in 1831.

Arago served as the director of the Paris Observatory from 1830. As an astronomer, he was among the first to explain the scintillation of stars using interference phenomena. He was also able to provide vital stimulus to young astronomers, including Frenchman Urbain Le Verrier.