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| Jean Baptiste Biot |
Born: 21 April 1774 in Paris, France
Died: 3 Feb 1862 in Paris, France
Jean-Baptiste Biot's father was Joseph Biot, whose ancestors were
farmers in Lorraine, had achieved an important role working in the
Treasury. Jean-Baptiste was educated at the college of Louis-le-Grand in
Paris, where he specialised 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 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 (we have to be thankful for photocopiers!) 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 Chausées 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 realised 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, befriending a fellow
student, Siméon-Denis Poisson, and graduated in 1797. He had found a
patron in Sylvestre-François Lacroix who was highly influential in
helping Biot develop his career.
He became Professor of Mathematics at the École Centrale de l'Oise at
Beauvais in 1797. It might seems remarkable that even someone as able as
Biot could move from being an undergraduate straight into a
professorship. However, things had worked in his favour [7]:-
The Convention, in a law of 25 February 1795 had called for a system of écoles centrales, one in each large town, to replace the collèges of the ancien régime as seats of secondary education. The curricula of the new schools was practical and modern and included two years devoted to mathematics, experimental physics and chemistry. These subjects had never been taught before on a high school level, so, inevitably, there was a shortage of qualified teachers.
Biot got to know of the vacant mathematics professorship through his
friendship with Barnabé Brisson, the son of Antoine François Brisson de
Beauvais, while studying at l'École Polytechnique. Through Barnabé
Brisson, Biot had got to know his sister Gabrielle. Although Gabrielle
was only sixteen years old, they married in 1797 soon after Biot took up
his position at Beauvais. Biot taught Gabrielle mathematics and physics
so that she might translate into French a German text by Ernst
Gottfried Fischer. It was Claude Louis Berthollet who had asked Biot to
make the translation which was published as Physique mécanique in
1806. Biot's wife was well educated and fluent in German, so her
translation was excellent. However, in line with the practice of the
time, the book records Biot himself as the translator rather than his
wife. Biot and his wife had a son Edouard Constant Biot who was born in
1803.
It was largely through Lacroix that Biot had been appointed at Beauvais
and Lacroix advised him frequently through the first years that he
worked there. However, he also managed to get support in his career from
Laplace. In fact in late 1799 Biot approached Laplace, who had taught
him at l'École Polytechnique, and offered to proof-read the Mécanique céleste
which at that time was with the publisher. He didn't give up when
Laplace said "No thanks" but persisted in a polite way and eventually
Laplace agreed. Biot was, by this time, an entrance examiner at the
École Polytechnique so was frequently in Paris. He wrote [7]:-
From that time on, each time I went to Paris I brought my proof-reading work and personally presented it to M Laplace. He always received it with kindness, examined it and discussed it, and that gave me the opportunity to submit to him the difficulties that had stopped me. His willingness to explain them was boundless. But even he could not always do it without stopping to think for a long while. This usually occurred in places where he had used the expedient phrase 'it can easily be seen'.
Certainly the effort required by Biot was enormous. He wrote near the end of 1799 [7]:-
I spent all of my days at this work [proof-reading the 'Mécanique céleste'] which I felt to be important in several respects, and I hope I have succeeded. I worked like a devil to finish it on time, and 1 remained at the task eighteen hours in a row the last day, without eating or drinking. Finally, thank heaven, it is finished, and I can flatter myself that I understand the 'Mecanique celeste'. If this were to be the only benefit I would get from it, it would still be a lot.
Laplace was also interested in the research on mathematics which Biot
was undertaking and gave him advice both on the material and on getting
it published. In 1800 he was appointed Professor of Mathematical Physics
at the Collège de France, an appointment which was due mainly to the
influence of Laplace. In 1800 Biot was elected an associate to the First
Class of the Institute, replacing Jean Montucla who died in December
1799. Again Laplace's support was important to Biot in this election. In
January 1803 the Institut was reorganised and Delambre became perpetual
secretary, creating a vacancy in the Mathematics Section. Although Biot
had produced excellent mathematics memoirs in the years up to 1800, he
had concentrated on experimental physics from that time on. However,
presumably to improve his chances of gaining a place in the Mathematics
Section, he submitted a memoir on the axes of tautochronous curves just
before the election was to take place. It was sufficient to keep his
mathematical reputation high and he was elected on 11 April 1803.
The first balloon ascent made for scientific purposes was by Biot and
Joseph-Louis Gay-Lussac from the garden of the Conservatoire des Arts on
24 August 1804. They achieved a height of 4000 metres and measured
magnetic, electrical, and chemical properties of the atmosphere at
various heights. In 1806, again with the support of Laplace, Biot was
appointed as an assistant astronomer at the Bureau de Longitudes in
addition to his other roles. On 3 September of that year he set out with
François Arago to Formentera, in the Balearic Islands, to complete
earlier work begun there on calculating the measure of the arc of the
meridian. They were still undertaking measurements when, in May 1808,
Napoleon declared his brother Joseph Bonaparte as Spanish ruler and the
War of Independence began. Biot and Arago must have looked extremely
suspicious; two Frenchmen with sophisticated measuring instruments
working on Spanish territory. Biot fled back to France immediately.
Later in 1808, together with Claude-Louis Mathieu, he embarked on a
series of measurements of the length of the seconds pendulum at
different points on the meridian, in particular at Bordeaux and at
Dunkirk. Both Mathieu and Biot received a prize from the Académie des
Sciences in 1809 for this highly accurate work, and in 1812 they
received a second prize from the Academy for their achievements. In 1809
Biot was appointed Professor of Physical Astronomy at the Faculty of
Sciences. He held this position for over fifty years.
Biot studied a wide range of mathematical topics, mostly on the applied
mathematics side. He made advances in astronomy, elasticity, electricity
and magnetism, heat and optics on the applied side while, in pure
mathematics, he also did important work in geometry. He collaborated
with Arago on refractive properties of gases. Biot, together with Felix
Savart, discovered that the intensity of the magnetic field set up by a
current flowing through a wire varies inversely with the distance from
the wire. This is now known as Biot-Savart's Law and is fundamental to
modern electromagnetic theory. Morris Kline, reviewing [8], writes:-
Biot depended entirely upon experiments to determine the interaction of a magnet and a straight line of electrical current and then inferred a mathematical law concerning the force between current and magnet.
Light was the topic on which Biot devoted most time, making the major
discovery of the laws of rotary polarization by crystalline bodies.
Having discovered these laws he used them in analysis of saccharine
solutions using an instrument called a polarimeter which he invented.
For this work on the polarisation of light passing through chemical
solutions he was awarded the Rumford Medal of the Royal Society of
London in 1840. He had been elected as a foreign member of the Royal
Society in 1815.
One of his important works was Mémoire sur la figure de la terre (1827) which describes the shape of the Earth. Among his other major works we mention: Analyse de la mécanique céleste de M Laplace (1801); Traité analytique des courbes et des surfaces du second degré (1802); Recherches sur l'intégration des équations différentielles partielles et sur les vibrations des surfaces (1803); Essai de géométrie analytique appliqué aux courbes et aux surfaces de second ordre (1806); Recherches expérimentales et mathématiques sur les mouvements des molécules de la lumière autour de leur centre de gravité (1814); Traité de physique experimentale et mathématique (1816); Precis de physique (1817); (with Arago) Recueil d'observations géodésiques, astronomiques et physiques exécutées en Espagne et Écosse (1821); Mémoire sur la vraie constitution de l'atmosphère terrestre (1841); Traité élémentaire d'astronomie physique (1805); Recherches sur plusieurs points de l'astronomie égyptienne (1823); Recherches sur l'ancienne astronomie chinoise (1840); Études sur l'astronomie indienne et sur l'astronomie chinoise (1862); Essai sur l'histoire générale des sciences pendant la Révolution (1803); Discours sur Montaigne (1812); Lettres sur l'approvisionnement de Paris et sur le commerce des grains (1835); Traite d'astronomie physique (1850); and Mélanges scientifiques et littéraires (1858).
He tried twice for the post of Secretary to the Académie des Sciences
and to improve his chances for election to this post he wrote Essai sur l'Histoire Générale des Sciences pendant la Révolution.
However he lost out in 1822 to Fourier for this post, then again when
Fourier died in May 1830 he applied again for the post of Secretary,
only to lose to Arago on this occasion. The rivalry between Arago and
Biot was again evident in 1839 when different photographic processes
were competing [10]:-
Arago and Biot, France's leading authorities in the field of optics, had spent the past thirty years disagreeing about the ability of optical instruments to represent the world. Photography became one more opportunity for them to disagree, and they did not shrink from the task. The debate extended beyond questions of assigning priority and apportioning credit. At its heart was the question of what the photographic surfaces showed, what relation the visible inscription bore to the real world.
Arago supported the Daguerre photographic process with silver plates
while Biot championed an approach with paper soaked in a silver solution
as developed by Henry Fox Talbot. This was not because he thought this
process produced clearer photographs, rather it was because he believed
that the images captured 'chemical radiation' invisible to the eye. We
should note that the idea of 'chemical radiation' was widely believed at
this time. Biot also believed that the photographic process should be
one reserved for scientific use and not made available for public use.
There was a period of collaboration between Biot and Talbot, the two
exchanging letters frequently. Basically the photographic process became
another tool for Biot to use in his investigations of light which had
always been a major interest to him.
As well as interests in almost every branch of science, Biot was
interested in the history of the subject. He published works on this
topic such as: Essai sur l'histoire générale des sciences pendant la Révolution française (1803); Notice historique sur la vie et les ouvrages de Newton (1822); Recherches sur plusieurs points de l'astronomie égyptienne appliquées aux monuments astronomiques trouvés en Égypte (1823); Sur la manière de calculer les positions des étoiles relativement à l'équateur et à l'écliptique pour les époques anciennes (1823); Opuscule sur l'Astronomie ancienne des Chinois, des Indous et des Arabes (1840); Mémoire sur le Zodiaque de Denderah (1844); Précis de l'histoire de l'Astronomie planétaire (1847); and Études sur l'astronomie indienne et l'astronomie chinoise (1862).
In [4] St Beuve says that Biot was endowed to the highest degree with
all the qualities of curiosity, finesse, penetration, precision,
ingenious analysis, method, clarity, in short with all the essential and
secondary qualities, bar one, genius, in the sense of originality and
invention.
A contrasting comment by Olinthus Gregory in 1821 is:-
With regard to M Biot, I had an opportunity of pretty fully appreciating his character when we were together in the Zetland [= Shetland] Isles; and I do not hesitate to say that I never met so strange a compound of vanity, impetuosity, fickleness, and natural partiality, as is exhibited in his character.
In addition to the honours we mentioned above, Biot was also honoured by
being made chevalier of the Legion of Honour in 1814 and commander in
1849. He was elected to the to the Academy of Inscriptions and
Belles-Lettre in 1841 and to the French Academy in 1856.
Article by: J J O'Connor and E F Robertson
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