Jean-Baptiste Biot

Astronomer mathematician physicist scientist teacher

April 21, 1774 (age 87)

Paris, Ile-de-France, France

Biot was closely associated with many of the institutions for education and research that were a prominent feature of France after the Revolution. On graduation from the École Polytechnique in 1797, he was appointed a professor of mathematics at the École Centrale of the Oise department at Beauvais. From 1799 he was an entrance examiner for the École Polytechnique, a post he retained when, in 1800, he was appointed a professor of mathematical physics at the Collège de France. Under the patronage of Laplace, Biot was given the post of assistant astronomer at the Bureau des Longitudes in 1806. When the University of France was established by Napoleon in 1808, Biot was appointed a professor of astronomy at the Paris Faculté des Sciences. From 1816 to 1826, however, while retaining the official title of professor of astronomy, he agreed to teach physics related to his own research and gave courses on light, sound, and magnetism. Throughout his life Biot made contributions to literature beyond those expected of a man of science. His Essai sur l’histoire générale des sciences pendant la révolution française was published in 1803. When in 1812 the Académie Française proposed the subject of Montaigne for a prize, Biot’s essay received an honorable mention. He was commissioned to write a hundredpage biography of Newton for the Biographie universelle. Biot was well known as an ardent follower of Newton. In 1813, in the Journal de physique, he described Newton as a person “whose conceptions seem to have surpassed the limits of thought of mortal man” (p.131). Biot continued: “Words fail to convey the profound impression of astonishment and respect which one experiences in studying the work of this admirable observer of nature.” In the biography, Biot’s solution to the problem of the interrelation of Newton’s natural philosophy and his theology was to suggest that all the original scientific work had been completed early in Newton’s life and that he had become seriously interested in theology only after mental illness. Biot later took issue with Brewster’s interpretation of Newton. In the last years of his life, Biot wrote appreciations of Gay-Lussac and Cauchy. Biot was the author of several important textbooks. His Traité élémentaire d’astronomie physique was the source from which Sir George Airy, later British astronomer royal, learned his basic astronomy; and he claimed that he had acquired his interest in the subject through Biot’s work. Biot’s Traité de physique (1816) constitutes a comprehensive account of contemporary physics, including not only recent original research by himself (e.g., on polarization) but also the recent and often unpublished work of his associates, particularly Laplace, Gay-Lussac, and Dulong. Although Biot’s first publications were in mathematics, he soon came strongly under the influence of Laplace, whose advice he followed in the application of analysis to physical problems. In 1802 Biot demonstrated that the attraction of an ellipsoid at an external point might be deduced by simple differentiations from a particular expression, which is theoretically known when the attraction is known for all points situated in the plane of one of the principal sections. Biot’s memoir, however, constituted little more than a commentary on the earlier writings of Legendre and Laplace. His introduction to Laplace had come about through his offer to read the proofs of Laplace’s Mécanique céleste. Laplace encouraged Biot to undertake experimental investigation of a wide range of problems, many of which constituted a deliberate extension of the Newtonian framework of science. This can be seen particularly in Biot’s research on refraction, polarization of light, and sound. If we were to select any one branch of physics to which Biot made the most important contribution, the choice would be the polarization of light, but, since none of his contributions in this field occurred before 1812, it will be convenient to deal first with his varied contributions to other branches of physical science. An unusual piece of research at the beginning of Biot’s career was concerned with a meteorite said to have fallen from the sky at l’Aigle in the Orne department on 26 April 1803. Biot was ordered by Chaptal, minister of the interior, to confirm the report. Shortly before, M. A. Pictet had called attention to reports of meteorites - reports that many rationalists had dismissed as superstitious. Biot questioned people in the locality where the meteoric stones had fallen. Various specimens were examined and compared with the composition of the ground from which they had been taken, and some were subjected to chemical analysis. Biot’s report read to the First Class of the Institute on 18 July 1803, marks the beginning of a general recognition in France of the reality of meteorites. In the years 1804–1809 Biot undertook several scientific projects in collaboration with other men, notably fellow members of the Arcueil group or the Bureau des Longitudes. On 24 August 1804, Biot made a balloon ascent with Gay-Lussac. The ascent was notable in that it was undertaken entirely for purposes of scientific research and had the approval of the French government. The primary purpose was to find whether the magnetic intensity of the earth decreased at great altitudes, as had been suggested by Horace de Saussure’s experiments in the Alps. From their experiments, in which they timed the oscillations of a magnetized needle at various altitudes, Biot and Gay-Lussac concluded that up to 4,000 meters there was no change. Biot undertook further work on magnetism in collaboration with Humboldt, who furnished much of the data used in their joint memoir (1804). Biot attempted to derive general laws governing inclination, using as a basis the hypothesis of an infinitely small magnet situated at the center of the earth and placed perpendicular to the magnetic equator. The theoretical values for the inclination agreed well with Humboldt’s readings, particularly in the northern hemisphere. Anomalies were attributed to purely local factors. In 1804 Biot carried out an experimental investigation of the conductivity of metal bars by maintaining one end at a known high temperature and taking readings of thermometers placed in holes along the bar. He was able to report the significant result that the steady-state temperature decreased exponentially along the length of the bar. He saw that this could be explained in terms of a balance of loss of heat at the surface and transfer of heat along the bar, which he analyzed in terms of adjacent pairs of cross-sectional areas. Unfortunately he was unable to present the differential equation corresponding to his physical model because of his inability to find plausible physical reasons for dividing a second difference of temperatures by the square of the infinitesimal element of length. Hence he could not convert his second difference into a second derivative. Biot collaborated with Arago in 1805–1806 in research which, in a typically Newtonian spirit, they presented with the title“Mémoire sur les affinités des corps pour la lumière, et, particulièrement sur les forces réfringentes des différents gaz” (1806). The accurate determination of the refractive indices of various gases and vapors at different pressures was a legitimate subject of study for two members of the Bureau des Longitudes who were concerned with astronomical observations. In another memoir, Biot reported on the refraction of light rays near the horizon. He made a full study of mirages, taking the subject beyond Wollaston’s work of 1803. In later years, in a succession of memoirs, Biot made further contributions to the subject of atmospheric refraction. As regards the joint work with Arago, however, not the least important part of Biot’s research was the accurate determination of the densities of gases weighed in glass globes. The values obtained were part of the data used by Gay-Lussac to establish his law of combining volumes of gases. When Gay-Lussac and the chemist Thenard carried out combustion analyses of organic compounds, they calculated their results with atomic weights for carbon and hydrogen deduced from the density measurements of Biot and Arago. Prout also used the data of Biot and Arago to support his hypothesis. In 1807 Biot collaborated with Thenard in a thorough comparative study of rhombic aragonite and hexagonal calcite. Apart from obvious chemical tests, they compared the refractivity not only of the crystals but also of their solutions in hydrochloric acid and of the carbon dioxide evolved from each. They concluded that aragonite and calcite were composed of the same chemical elements in the same proportions, but with a different arrangement of the molecules, which resulted in physically different substances. This was one of the earliest examples of what was later called dimorphism. In 1806 Biot and Arago were sent by the Bureau des Longitudes to determine the arc of the meridian in Spain and the Balearic Islands, a task begun by Mdchain but left incomplete at his death in 1804. The post-Revolution metric system was based on the idea of a “natural” unit, the meter, which was supposed to be exactly one ten-millionth of a meridian quadrant of the earth. Mechain and Delambre had made measurements over a meridian arc of 10° stretching from Dunkirk to Barcelona, and from their readings the length of the standard meter was obtained. It was proposed that this should be redetermined with greater accuracy by extending measurements farther south to the Balearic Islands. Special difficulties in triangulation were encountered because of the distance of the islands from the mainland, but these difficulties were eventually overcome. Biot presented a report on this expedition to the Institute in 1810. Meanwhile, in the company of Mathieu, Biot measured the length of the seconds pendulum at Bordeaux and at Dunkirk. In 1817, Biot took part in another expedition, this time to Scotland and the Shetland Islands in order to confirm the geodesic work that had recently been undertaken by the British under Colonel Mudge. In 1818, Biot was again in Dunkirk; in 1824 and 1825 he went to Italy and Sicily with his son, and then revisited Formentera and Barcelona to correct his earlier geodesic measurements. From a comparison of his determinations, Biot concluded that the weight of a given body is not the same on all points with the same latitude, nor is its variation uniform along a particular meridian. This work established the necessity of revising the generally accepted simple ellipsoid theory of the earth. During Biot’s visit to Spain in 1806 and 1807 for geodesic work, he carried out other experimental work which is not generally known. He made a special study of the composition of the air contained in the swim bladders of fish found off the islands of Ibiza and Formentera. He can claim credit for recording the extremely high proportion of oxygen in the swim bladders of certain fish which live at great depths. He found a maximum of 87 percent oxygen, a figure that agrees well with the modern value. He did his most important work in the study of the polarization of light. The polarization of light by reflection had been discovered by Malus in Paris in the fall of 1808. This was of fundamental importance in the history of optics since it showed that a phenomenon that had previously been observed in a few crystalline substances, such as Iceland spar, was a general property of light. Malus’s discovery opened up an entirely new field of research, and no one was stimulated more than his two associates in the Arcueil group, Arago and Biot. In August 1811, Arago announced that he had found that white light polarized by reflection could, on passing through certain crystals, be split into two differently colored beams. In 1832 Biot recorded the property of a solution of tartaric acid of rotating polarized light, and he remarked on the anomalous dispersion it gave, the rotation being greater for “less refrangible rays.” In 1836 he presented to the Academy a memoir devoted entirely to the study of the rotatory power of tartaric acid under different conditions.

Jean-Baptiste Biot Edit Profile

Astronomer mathematician physicist scientist teacher

Background

Jean-Baptiste Biot was born on April 21, 1774, in Paris, Île-de-France, the son of Joseph Biot, whose ancestors were farmers in Lorraine, had achieved an important role working in the Treasury.

Education

Biot was educated at the Lycée Louis-le-Grandin Paris, where he specialized in classics. He completed his studies at Louis-le-Grand in 1791 following which, since his father wanted him to make a career in commerce, he took private lessons in mathematics from Antoine-Rene Mauduit who was a professor of mathematics at the Collège de France. Joseph Biot then sent his son to Le Havre to become a clerical assistant to a merchant. His job there consisted of copying vast numbers of letters, which bored Biot so much that he volunteered for the army.

He joined the French army in September 1792 and served in the artillery at the Battle of Hondschoote in September 1793. In this battle, the French defeated the British and Hanoverian soldiers besieging Dunkirk.

After the battle Biot, suffering from an illness, decided to leave the army and return to his parents. As he was walking towards Paris, he was befriended by an important person who passed in his carriage. He took Biot in his carriage to Paris where he (Biot) was arrested as a deserter (he was still in uniform) and brought before a revolutionary committee. This would have had serious consequences for Biot had not the stranger intervened and he was set free. Despite Biot's efforts, he was not able to identify the important stranger and thank him.

It took Biot some months to recover from the illness during which time he continued with his studies of mathematics. He took the entrance examinations for the École des Ponts et Chaussées (now École des ponts ParisTech) and was accepted in January 1794. The École Polytechnique was founded later in 1794 (actually named École centrale des travaux publics for its first year) and Biot transferred there in November of that year. Gaspard Monge, one of the founders of l'École Polytechnique who taught the first intake of students, quickly realized Biot's potential. Biot, however, quickly became involved in student politics and was made a section leader. There was an attempted insurrection by the royalists against the Convention and Biot took part. He was captured by government forces and taken prisoner. Had it not been for Monge, who could not see someone with such talents remain in jail, or even die, pleading successfully for his release his promising career might have ended. It is not surprising that for a second time he had come close to a death sentence, giving the dangerous times in Revolutionary France through which he lived. He returned to his studies at the École Polytechnique and graduated in 1797.

$Education period of Jean-Baptiste Biot in Lyc\u00E9e Louis-le-Grand$

Education period of Jean-Baptiste Biot in Ecole des Ponts ParisTech

Education period of Jean-Baptiste Biot in Ecole polytechnique

Career

Biot was closely associated with many of the institutions for education and research that were a prominent feature of France after the Revolution. On graduation from the École Polytechnique in 1797, he was appointed a professor of mathematics at the École Centrale of the Oise department at Beauvais. From 1799 he was an entrance examiner for the École Polytechnique, a post he retained when, in 1800, he was appointed a professor of mathematical physics at the Collège de France. Under the patronage of Laplace, Biot was given the post of assistant astronomer at the Bureau des Longitudes in 1806. When the University of France was established by Napoleon in 1808, Biot was appointed a professor of astronomy at the Paris Faculté des Sciences. From 1816 to 1826, however, while retaining the official title of professor of astronomy, he agreed to teach physics related to his own research and gave courses on light, sound, and magnetism.

Throughout his life Biot made contributions to literature beyond those expected of a man of science. His Essai sur l’histoire générale des sciences pendant la révolution française was published in 1803. When in 1812 the Académie Française proposed the subject of Montaigne for a prize, Biot’s essay received an honorable mention. He was commissioned to write a hundredpage biography of Newton for the Biographie universelle. Biot was well known as an ardent follower of Newton. In 1813, in the Journal de physique, he described Newton as a person “whose conceptions seem to have surpassed the limits of thought of mortal man” (p.131). Biot continued: “Words fail to convey the profound impression of astonishment and respect which one experiences in studying the work of this admirable observer of nature.” In the biography, Biot’s solution to the problem of the interrelation of Newton’s natural philosophy and his theology was to suggest that all the original scientific work had been completed early in Newton’s life and that he had become seriously interested in theology only after mental illness. Biot later took issue with Brewster’s interpretation of Newton. In the last years of his life, Biot wrote appreciations of Gay-Lussac and Cauchy.

Biot was the author of several important textbooks. His Traité élémentaire d’astronomie physique was the source from which Sir George Airy, later British astronomer royal, learned his basic astronomy; and he claimed that he had acquired his interest in the subject through Biot’s work. Biot’s Traité de physique (1816) constitutes a comprehensive account of contemporary physics, including not only recent original research by himself (e.g., on polarization) but also the recent and often unpublished work of his associates, particularly Laplace, Gay-Lussac, and Dulong.

Although Biot’s first publications were in mathematics, he soon came strongly under the influence of Laplace, whose advice he followed in the application of analysis to physical problems. In 1802 Biot demonstrated that the attraction of an ellipsoid at an external point might be deduced by simple differentiations from a particular expression, which is theoretically known when the attraction is known for all points situated in the plane of one of the principal sections. Biot’s memoir, however, constituted little more than a commentary on the earlier writings of Legendre and Laplace. His introduction to Laplace had come about through his offer to read the proofs of Laplace’s Mécanique céleste. Laplace encouraged Biot to undertake experimental investigation of a wide range of problems, many of which constituted a deliberate extension of the Newtonian framework of science. This can be seen particularly in Biot’s research on refraction, polarization of light, and sound. If we were to select any one branch of physics to which Biot made the most important contribution, the choice would be the polarization of light, but, since none of his contributions in this field occurred before 1812, it will be convenient to deal first with his varied contributions to other branches of physical science.

An unusual piece of research at the beginning of Biot’s career was concerned with a meteorite said to have fallen from the sky at l’Aigle in the Orne department on 26 April 1803. Biot was ordered by Chaptal, minister of the interior, to confirm the report. Shortly before, M. A. Pictet had called attention to reports of meteorites - reports that many rationalists had dismissed as superstitious. Biot questioned people in the locality where the meteoric stones had fallen. Various specimens were examined and compared with the composition of the ground from which they had been taken, and some were subjected to chemical analysis. Biot’s report read to the First Class of the Institute on 18 July 1803, marks the beginning of a general recognition in France of the reality of meteorites.

In the years 1804–1809 Biot undertook several scientific projects in collaboration with other men, notably fellow members of the Arcueil group or the Bureau des Longitudes. On 24 August 1804, Biot made a balloon ascent with Gay-Lussac. The ascent was notable in that it was undertaken entirely for purposes of scientific research and had the approval of the French government. The primary purpose was to find whether the magnetic intensity of the earth decreased at great altitudes, as had been suggested by Horace de Saussure’s experiments in the Alps. From their experiments, in which they timed the oscillations of a magnetized needle at various altitudes, Biot and Gay-Lussac concluded that up to 4,000 meters there was no change.

Biot undertook further work on magnetism in collaboration with Humboldt, who furnished much of the data used in their joint memoir (1804). Biot attempted to derive general laws governing inclination, using as a basis the hypothesis of an infinitely small magnet situated at the center of the earth and placed perpendicular to the magnetic equator. The theoretical values for the inclination agreed well with Humboldt’s readings, particularly in the northern hemisphere. Anomalies were attributed to purely local factors.

In 1804 Biot carried out an experimental investigation of the conductivity of metal bars by maintaining one end at a known high temperature and taking readings of thermometers placed in holes along the bar. He was able to report the significant result that the steady-state temperature decreased exponentially along the length of the bar. He saw that this could be explained in terms of a balance of loss of heat at the surface and transfer of heat along the bar, which he analyzed in terms of adjacent pairs of cross-sectional areas. Unfortunately he was unable to present the differential equation corresponding to his physical model because of his inability to find plausible physical reasons for dividing a second difference of temperatures by the square of the infinitesimal element of length. Hence he could not convert his second difference into a second derivative.

Biot collaborated with Arago in 1805–1806 in research which, in a typically Newtonian spirit, they presented with the title“Mémoire sur les affinités des corps pour la lumière, et, particulièrement sur les forces réfringentes des différents gaz” (1806).

The accurate determination of the refractive indices of various gases and vapors at different pressures was a legitimate subject of study for two members of the Bureau des Longitudes who were concerned with astronomical observations. In another memoir, Biot reported on the refraction of light rays near the horizon. He made a full study of mirages, taking the subject beyond Wollaston’s work of 1803. In later years, in a succession of memoirs, Biot made further contributions to the subject of atmospheric refraction. As regards the joint work with Arago, however, not the least important part of Biot’s research was the accurate determination of the densities of gases weighed in glass globes. The values obtained were part of the data used by Gay-Lussac to establish his law of combining volumes of gases. When Gay-Lussac and the chemist Thenard carried out combustion analyses of organic compounds, they calculated their results with atomic weights for carbon and hydrogen deduced from the density measurements of Biot and Arago. Prout also used the data of Biot and Arago to support his hypothesis.

In 1807 Biot collaborated with Thenard in a thorough comparative study of rhombic aragonite and hexagonal calcite. Apart from obvious chemical tests, they compared the refractivity not only of the crystals but also of their solutions in hydrochloric acid and of the carbon dioxide evolved from each. They concluded that aragonite and calcite were composed of the same chemical elements in the same proportions, but with a different arrangement of the molecules, which resulted in physically different substances. This was one of the earliest examples of what was later called dimorphism.

In 1806 Biot and Arago were sent by the Bureau des Longitudes to determine the arc of the meridian in Spain and the Balearic Islands, a task begun by Mdchain but left incomplete at his death in 1804. The post-Revolution metric system was based on the idea of a “natural” unit, the meter, which was supposed to be exactly one ten-millionth of a meridian quadrant of the earth. Mechain and Delambre had made measurements over a meridian arc of 10° stretching from Dunkirk to Barcelona, and from their readings the length of the standard meter was obtained. It was proposed that this should be redetermined with greater accuracy by extending measurements farther south to the Balearic Islands. Special difficulties in triangulation were encountered because of the distance of the islands from the mainland, but these difficulties were eventually overcome. Biot presented a report on this expedition to the Institute in 1810. Meanwhile, in the company of Mathieu, Biot measured the length of the seconds pendulum at Bordeaux and at Dunkirk. In 1817, Biot took part in another expedition, this time to Scotland and the Shetland Islands in order to confirm the geodesic work that had recently been undertaken by the British under Colonel Mudge. In 1818, Biot was again in Dunkirk; in 1824 and 1825 he went to Italy and Sicily with his son, and then revisited Formentera and Barcelona to correct his earlier geodesic measurements. From a comparison of his determinations, Biot concluded that the weight of a given body is not the same on all points with the same latitude, nor is its variation uniform along a particular meridian. This work established the necessity of revising the generally accepted simple ellipsoid theory of the earth.

During Biot’s visit to Spain in 1806 and 1807 for geodesic work, he carried out other experimental work which is not generally known. He made a special study of the composition of the air contained in the swim bladders of fish found off the islands of Ibiza and Formentera. He can claim credit for recording the extremely high proportion of oxygen in the swim bladders of certain fish which live at great depths. He found a maximum of 87 percent oxygen, a figure that agrees well with the modern value.

He did his most important work in the study of the polarization of light. The polarization of light by reflection had been discovered by Malus in Paris in the fall of 1808. This was of fundamental importance in the history of optics since it showed that a phenomenon that had previously been observed in a few crystalline substances, such as Iceland spar, was a general property of light. Malus’s discovery opened up an entirely new field of research, and no one was stimulated more than his two associates in the Arcueil group, Arago and Biot. In August 1811, Arago announced that he had found that white light polarized by reflection could, on passing through certain crystals, be split into two differently colored beams.

In 1832 Biot recorded the property of a solution of tartaric acid of rotating polarized light, and he remarked on the anomalous dispersion it gave, the rotation being greater for “less refrangible rays.” In 1836 he presented to the Academy a memoir devoted entirely to the study of the rotatory power of tartaric acid under different conditions.

Achievements

Jean-Baptiste Biot is remembered as a scientist who laid the basis for saccharimetry, a useful technique of analyzing sugar solutions. He also contributed to the study of polarized light and meteorites. The mineral biotite and Cape Biot in Greenland were named after Jean-Baptiste Biot.

Works

$Trait\u00E9 \u00C9l\u00E9mentaire d\'Astronomie Physique Trait\u00E9 \u00C9l\u00E9mentaire d\'Astronomie Physique$ $Trait\u00E9 de physique exp\u00E9rimentale et math\u00E9matique Trait\u00E9 de physique exp\u00E9rimentale et math\u00E9matique$ $M\u00E9langes scientifiques et litt\u00E9raires M\u00E9langes scientifiques et litt\u00E9raires$ $Pr\u00E9cis de l\'histoire de l\'astronomie chinoise Pr\u00E9cis de l\'histoire de l\'astronomie chinoise$

book

Religion

Under the influence of the ideas of the Revolution, and later of Laplace, Biot became skeptical of all belief in a personal God. Yet in 1825, in Rome, he sought and obtained a personal audience with Pope Leo XII and he became increasingly attracted to the religion of his childhood. In 1846 he made a formal return to the Roman Catholic Church.

Politics

Biot, who in his youth had detested the Jacobins, also had little sympathy for Napoleon. Unlike many of his contemporaries in France, Biot took no part in politics, living a long and active life devoted almost entirely to scientific research.

Views

Biot contributed greatly to the study of the polarization of light. He repeated Arago’s experiments and established the relationship between the thicknesses of the crystal plates and the colors produced. He observed that for perpendicular incidence, the colors seen correspond to those seen by reflection and transmission in thin films of air; and he concluded that the thicknesses at which the colors appeared were proportional to the thickness of the air gap that gave the same color on Newton’s scale. These thicknesses depended on the nature of the crystal but were always much greater than the thicknesses of thin films of air that gave the same tint. Biot found that the colors disappeared if the plate was extremely thin, and there was also an upper limit - for example, no colors would be seen if the thickness of a plate of gypsum was greater than 0.45 mm. In this research, the exact measurement of the plate was of the utmost importance, and Biot was fortunate in being able to use the spherometer, newly invented by Cauchoix. He began his research by taking eleven plates of gypsum, varying in thickness from 0.087 mm. to 0.345 mm. He determined the color produced by each and compared it with the color on Newton’s scale. For oblique incidence, Biot found that the color depended on the thickness of the crystal traversed by the refracted ray and varied as the square of the sine of the angle that the direction of the ray formed with the optical axis.

Biot’s interpretation of his results was in terms of a repulsive force that caused polarization by acting on the particles of light. This conception was first worked out in detail in a memoir presented to the First Class on 30 November 1812. The discovery of polarization had greatly encouraged Laplace, Biot, and others who supported a corpuscular theory of light. Malus had been successful in deriving the fundamental cosine law of polarization on such a model. To explain the complementary polarization in crystalline plates, Biot developed a theory of “mobile polarization.” The particles of a polarized ray were supposed to preserve their original polarization until they reached a certain depth in the crystal, when they began to oscillate around their center of gravity so that the axes of polarization were carried alternately to each side of the axes of the crystal. The period was considered to vary with the color (as in Newton’s theory of fits). When the ray emerged from the crystal, oscillation stopped, and the ray assumed “fixed polarization,” in which the axes of the particles were arranged in two perpendicular directions. The theory was plausible up to a point, but Biot had considerable difficulty in accounting for the difference in the effect of thin and thick plates on polarized light. In 1841 Biot considered that he had found a new phenomenon of polarization, which was dependent on the existence of different layers in the crystal and which he called lamellar polarization.

In 1812 Biot observed that the rotation of polarized light produced by a plate of quartz decreased progressively with change of color from violet to red. In a paper read to the Academy on 22 September 1818, Biot was able to announce what has become known as Biot’s law of rotatory dispersion.

In 1816 Biot suggested that the equal effect of polarized light on respective solutions of cane sugar and beet sugar constituted an additional proof of their identity. After 1820 he put his optical research aside, and for the next twelve years, his work was mainly in astronomy and electricity. From 1832 he resumed his optical research with renewed vigor, going back to his earlier work and carrying out comparative tests on sugars. In 1833, working with Persoz, Biot found that when cane sugar was heated with dilute sulfuric acid, a chemical change took place; this was revealed by the solution’s rotating the plane of polarized light to the left instead of to the right. He described the effect as “inversion,” a term which is still used. In further collaboration with Persoz, Biot studied the conversion of starch by dilute acids into sugar and a gum which, from its effect on polarized light, they named dextrine. Biot introduced the polarimetric method of quantitative estimation of sugar remaining in molasses.

Biot stressed that tartaric acid constituted an outstanding exception to his law of inverse squares (of wavelength). Biot accordingly divided optically active substances into two classes, those that obeyed his law and those that did not. He observed the crystalline forms of some salts of tartaric acid, but it was left to Pasteur to show the relationship between the crystalline form and the effect on polarized light. Biot was, significantly, an ardent champion of Pasteur at the beginning of his career. Pasteur, for his part, felt that Biot’s work on the rotation of polarized light by liquids constituted a valuable scientific tool that had been hitherto unjustly neglected by chemists.

Quotations: "Divided minds, getting lost on different paths, are losing the huge advantage that would result from their combined forces."

"The first step to be taken is to study carefully the fundamental phenomenon above described, and to examine all the various circumstances under which it presents itself."

Membership

Biot joined the Société Philomathique in Paris in 1801. His association with Laplace and Berthollet at about this time qualifies him for consideration as one of the original members of the Société d’Arcueil. In 1856 he received the honor, unusual for a man of science, of election to the Académie Française.

Société Philomathique

1801
Société d’Arcueil

1800
Académie Française

1856

Connections

In 1797, Jean-Baptiste Biot married Françoise-Gabrielle Brisson, the daughter of Antoine François Brisson of Beauvais, inspecteur général du commerce et des manufactures, whose son was Biot’s friend at the École Polytechnique. The couple had a son, Édouard Constant Biot.

Father:: Joseph Biot
Wife:: Françoise-Gabrielle Biot (Brisson)
Son:: Édouard Constant Biot
Friend:: Barnabé Brisson
colleague:: Joseph Louis Gay-Lussac
colleague:: François Arago
colleague:: Félix Savart
colleague:: Pierre-Simon Laplace

References

Dictionary of scientific biography

Main Photo