Jean-Baptiste Biot

French physicist and mathematician

• Born: April 21, 1774; Paris, France
• Died: February 3, 1862; Paris, France

Jean-Baptiste Biot’s research helped define the fields of modern physics and mathematics. He contributed significantly to the current understanding of meteorites, optics, and the physics of light. Biot worked with numerous prominent physicists and other scientists in nineteenth-century France and contributed his scientific understanding to numerous pivotal discoveries.

Primary field: Physics

Specialties: Optics; astrophysics

Early Life

Jean-Baptiste Biot (ZHAN-ba-teest BEE-oh) was born into an agricultural family in the Lorraine region of France. Biot’s father, Joseph Biot, had opted for civil service and worked his way to a position in the treasury. He paid for a private tutor to teach his son mathematics, hoping his son would follow in his footsteps in commerce. Biot then attended the Louis-le-Grande school in Paris, graduating with a degree in classical studies in 1791.

Disenchanted with his studies and the career his father had planned for him, Biot enlisted in the recently established army of the First French Republic in 1793. At the time France was weakened by the Revolution that had raged on for six years. The nation faced threats from British and Hanoverian (German) forces intent on unseating the First Republic during what is now called the Campaign of Flanders. Biot served as a member of the artillery forces on the front lines during the Battle of Hondschoote in September of 1793, helping to repel enemy forces attempting a siege on Dunkirk. Biot fell ill following the battle and, after being jailed briefly as a deserter, managed to convince the army of his illness. He was allowed to return to his home, where he recovered and resumed his studies.

In 1794, Biot was accepted to the École des Ponts et Chaussées, transferring later that year to the newly established École Polytechnique. The school had been established to train French intellectuals for civil service but had quickly become the leading science and engineering school in France. France was rapidly changing with the institution of the National Convention in 1792 as the leading legislative body after the fall of the monarchy. In 1794, Biot took part in a student-led royalist insurrection against the convention and he was imprisoned. Under the newly adopted laws of France, Biot would have been sentenced to death, but his teachers intervened on his behalf and secured his release. Biot graduated in 1797 and became a professor of mathematics at the École Centrale de l’Oise Beauvais.

A few years later, Biot played a major role in helping his colleague Pierre-Simon Laplace publish his Traité de Mécanique Céleste (Treatise on celestial mechanics, 1799–1805), and Laplace became an ardent supporter of Biot’s career, helping his protégé to achieve a position as professor of mathematical physics at the Collège de France in 1800.

Life’s Work

Though he published several papers on mathematics as a student, Biot’s major contributions to science came after he took his professorship in 1800, when he began to transfer his skills in mathematics to applied research. In 1804, Biot and Joseph-Luis Gay-Lussac became the first scientists to launch a balloon for the purposes of studying atmospheric properties and the magnetic field of the Earth.

In 1803, a series of meteorites struck the Earth at L’Aigle in northwestern France. Biot was sent to investigate the mysterious “fireballs” and conducted detailed measurements and chemical analyses of the rock fragments he found at the site. German physicist Ernst Chladni published a paper in 1794, in which he theorized that the fireballs observed were the result of extraterrestrial objects falling from space into the Earth’s atmosphere. Chladni’s explanation was not widely believed in France until Biot published a series of papers, Traité élémentaire d’astronomie physique (Elementary treatise on physical astronomy), in 1805 providing further proof for the extraterrestrial origin of meteorites. That publication would become his best-known work.

Around 1806, Biot began to develop a great interest in optics and the physics of light. This was partially due to an 1804 paper by English physicist Thomas Young, which revived the theory that light was composed of waves, while the popular theory of the time held that light was composed of particles, called corpuscles. Biot and his colleague, physicist Dominique-François Arago, developed an intense rivalry over their opposing theories of light, as Biot favored the corpuscle theory and Arago favored the wave model. Biot and Arago still worked together, however, developing the Fortuna Apparatus, a tool for studying the properties of light by focusing beams of light through various gases.

After Etienne-Luis Malus’s discovery of the polarization of reflected light in 1808, Biot began a detailed study of the subject, ultimately hoping to gather support for the corpuscle theory. In 1815, Biot published the results of years of research indicating that polarized light (light particles falling on the same plane) will be rotated either clockwise or counterclockwise when they pass through the object creating the polarization. This discovery was later called Biot’s Law of Rotary Polarization.

Biot’s contribution to the understanding of polarization was a major advancement in the study of optics, ultimately allowing for the development of modern optical technology, such television and computer screens and photographic lenses. Biot developed his own tool for his experiments, called a polarimeter, which he used to further study refraction through liquid saccharine solutions. Biot would later receive honors from French and British scientific institutions for his work on polarization. Though Biot and Arago were rivals throughout the remainder of their careers, they still collaborated on certain projects, including the publication of Précis Élémentaire de Physique Experimentale (1817), an introductory text covering the study of physics.

Another major breakthrough attributed to Biot came from his study of electricity and magnetism with his friend and colleague, physicist Felix Savart, who went on to make major contributions to the field of acoustic physics. In 1820, Biot and Savart created the Biot-Savart Law, a mathematical formula that can be used to calculate both the direction and the magnitude of a magnetic field produced by an electric current. The understanding of this mathematical relationship was a critical step in the development of the modern theory regarding the relationship between electricity and magnetism.

Impact

Biot is primarily remembered for his contribution to the study of light and magnetism, but his reach extended into every scientific field of the era. Biot published work in general physics, astronomy, and applied mathematics, making a variety of major and minor contributions to various fields of inquiry. His work on light refraction and polarization is considered a major step in the development of engineering, eventually allowing for technological innovations that utilized polarization in optical design. In addition, Biot’s research contributed to the early work of French chemist Louis Pasteur in his application of optics to chemical processes, thus largely leading to the pasteurization process.

Biot was elected to the French Academy of Sciences in 1856, then the most prestigious society of scientists in France. He was also elected to the Royal Academy of Britain and was awarded the Rumford Medal from the British Royal Academy in 1840. During his life, Biot collaborated with many of the major innovators in French scientific discourse. The elite of French academia often communicated in semi-casual societies where members met and discussed major issues in science, politics, and society. Biot was a prominent member of these groups from the turn of the century until his death, and his scientific view most likely made an impact on a variety of issues that have not necessarily been linked to his direct influence. Biot was also a student of scientific history, publishing books on the history of science prior to the French Revolution and the first biographical account of Sir Isaac Newton’s life and scientific contributions (1829).

Since his death, in 1862, Biot’s contributions to science have been recognized on an international scale. The mineral biotite, a silicate mineral in the mica family, was named in his honor, as Biot was one of the first to study the optical properties of micas. His name has also been given to one of the craters of the moon and to several buildings, avenues, and institutions throughout France.

Bibliography

Frankel, Eugene. Jean-Baptiste Biot:The Career of a Physicist in Nineteenth Century France. Princeton: Princeton UP, 1972. Print. A detailed biography of Biot’s life prepared as historian Eugene Frankel’s thesis at Princeton University.

Levitt, Theresa. The Shadow of Enlightenment: Optical and Political Transparency in France (1749–1848). New York: Oxford UP, 2009. Print. A historical account of the lives of Biot and Arago and a coverage of their friendship and rivalry over issues surrounding light and optics.