Jean-Baptiste Biot, physicist, astronomer and mathematician, was born April 21, 1774 in Paris. His father, who descended from a peasant family of Lorraine, worked for the Royal Treasury. While studying at the prestigious College Louis-le-Grand in Paris, Jean-Baptiste drew the attention of the mathematician Antoine-René Mauduit (1731-1815) who gave him private lessons. Yet his father sent him to Le Havre into apprenticeship with a merchant. His work consisted mainly of copying letters. He ran away and, at age 18, he joined the Army of the Revolution as a volunteer cannoneer and was injured at the Battle of Hondschoote, which liberated Dunkirk from the armies of the First Coalition of European powers which were attacking the Revolution. He returned to his family with a permanently damaged knee, got involved in political protests, even marched against the Convention on 13 Vendémiaire, and was accused of being a deserteur and jailed. The mathematician Gaspard Monge, the inventor of descriptive geometry and an important Jacobine, got him out of trouble.

He started to study higher mathematics, entering the engineering school of the Ponts et Chaussées ("bridges and roads"), and became an engineer of public works. For four years, he taught mathematics at Beauvais. He became close friends with the mathematician and engineer Barnabé Brisson (1777-1828), who would become one of the foremost engineers and canal-builders in France, and whose sister he married in 1797 (Brisson himself married a niece of Gaspard Monge.) A protégé of the astronomer and mathematician Laplace, Biot became titulary of the chair of mathematical physics at the College de France in 1800, at age 26.

In 1803, Biot investigated the fall of the L'Aigle météorite, and demonstrated in his report the exoterrestrial origin of meteorites, which made him famous all over Europe.

The following year, 1804, he undertook a perilous ascension in a hydrogen balloon with the chemist Louis Joseph Gay-Lussac (1778-1750) in order to study the electric, magnetic and chemical properties of the atmosphere, and especially to determine the inclination of the Earth's magnetic field. Until 1826, he shared with Gay-Lussac the teaching of the course of physics at the Faculté des Sciences in Paris. In 1809, he became the titulary of the chair of astronomy there.

In 1812, Biot turned his attention to the study of optics, particularly the optical properties of mica, and studied the polarization of light. His work in chromatic polarization and rotary polarization greatly advanced the field of optics and has led to many breakthroughs, such as liquid crystal displays (LCDs), which are used on television and computer screens, and polarizing filters, used in photography.

Gay-Lussac and Jean-Baptiste Biot in hydrogen balloon 1804 studying earth magnetic field

Gay-Lussac and Biot aboard a hydrogen-balloon in 1804 (late XIXth century lithography)

Always a "hands-on" scientist, he undertook several expeditions for geodetic measurements in France, Spain, Scotland and Illyria, a.o. prolonging the measurements of the Paris Meridian (then the primary meridian) to the Shetland Islands and the Balearics. Armed with a Borda-pendulum, he studied gravimetry (measuring the strength of the gravitational field) at the 45th parallel in Bordeaux.

In 1820, together with Francesco Carlini, he determined for the first time the vertical deflection of the gravity field through measurements at the top of Mont Cenis, in the French Alps.

Also in 1820, together with the physicist Felix Savart, he formulated the law of Biot-Savart, an equation that describes the magnetic field generated by an electric current, relating it to the magnitude, direction, length and proximity of the electric current.

Biot considered that written expression was an indispensible companion to scientific reflexion and was a fecund writer. He was interested in the sciences of Antiquity, particularly Egyptian astronomy, and wrote, among others, a memoir about the Zodiac of Denderah.

Jean-Baptiste Biot

His son Edouard (1803-1850) translated books of Charles Babbage into French and made his mark both in railroad engineering (Manual of Railway Construction, 1834) and as a sinologist. He translated the 11th century B.C. Zhou Li, the "Rites of Zhou," of the Book of Rites. He died prematurely, at 46, possibly of grief after the death of his wife, and his father brought the work to completion and supervised its publication. It remains the translation of reference.

Few scientists were as much honored during their life time as Jean-Baptiste Biot. The name "biotite" was given to a certain kind of mica in honor of his work in optics. The Biot number, a dimensionless number (abbreviated Bi) is used in thermodynamics in heat transfer calculations. A now disused unit of measure of the electric current, the Biot, was also named after him (1 Biot = 10 Ampères).

Besides the French Legion of Honor, and the Prussian Order "Pour le Mérite," he also received the Rumford Medal. He was a member of the Royal Society of London (1815), of the Royal Academy of Sciences of Stockholm (1816), the Academy of Sciences of Saint-Petersburg (1818), the Royal Academy of Sciences of Berlin (1820), the American Academy of Arts and Sciences of Boston (1822), the Academy of Sciences of Catania (1825), the Royal Astronomical Society of London (1832), the Philosophical and Literary Academy of Saint Andrews, Scotland (1838), to name but a few...

The year of his death, in 1862, at the age of 88, he published a book of studies on Indian and Chinese astronomy.

Jean-Baptiste Biot