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Pierre-Simon LaplaceArticle by: J J O'Connor and E F RobertsonFrom: http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Laplace.htmlPierre-Simon Laplace's father, Pierre Laplace, was comfortably well off in the cider trade. Laplace's mother, Marie-Anne Sochon, came from a fairly prosperous farming family who owned land at Tourgéville. Many accounts of Laplace say his family were 'poor farming people' or 'peasant farmers' but these seem to be rather inaccurate although there is little evidence of academic achievement except for an uncle who is thought to have been a secondary school teacher of mathematics. This is stated in [1] in these terms:-
Laplace attended a Benedictine priory school in Beaumont-en-Auge,
as a day pupil, between the ages of 7 and 16. His father expected
him to make a career in the Church and indeed either the Church
or the army were the usual destinations of pupils at the priory
school. At the age of 16 Laplace entered Caen University. As he
was still intending to enter the Church, he enrolled to study theology.
However, during his two years at the University of Caen, Laplace
discovered his mathematical talents and his love of the subject.
Credit for this must go largely to two teachers of mathematics at
Caen, C Gadbled and P Le Canu of whom little is known except that
they realised Laplace's great mathematical potential.
He began producing a steady stream of remarkable mathematical papers,
the first presented to the Académie des Sciences in Paris
on 28 March 1770. This first paper, read to the Society but not
published, was on maxima and minima of curves where he improved
on methods given by Lagrange. His next paper for the Academy followed
soon afterwards, and on 18 July 1770 he read a paper on difference
equations. The year 1771 marks Laplace's first attempt to gain election to the Académie des Sciences but Vandermonde was preferred. Laplace tried to gain admission again in 1772 but this time Cousin was elected. Despite being only 23 (and Cousin 33) Laplace felt very angry at being passed over in favour of a mathematician who was so clearly markedly inferior to him. D'Alembert also must have been disappointed for, on 1 January 1773, he wrote to Lagrange, the Director of Mathematics at the Berlin Academy of Science, asking him whether it might be possible to have Laplace elected to the Berlin Academy and for a position to be found for Laplace in Berlin. Before Lagrange could act on d'Alembert's request, another chance for Laplace to gain admission to the Paris Academy arose. On 31 March 1773 he was elected an adjoint in the Académie des Sciences. By the time of his election he had read 13 papers to the Academy in less than three years. Condorcet, who was permanent secretary to the Academy, remarked on this great number of quality papers on a wide range of topics. We have already mentioned some of Laplace's early work. Not only had he made major contributions to difference equations and differential equations but he had examined applications to mathematical astronomy and to the theory of probability, two major topics which he would work on throughout his life. His work on mathematical astronomy before his election to the Academy included work on the inclination of planetary orbits, a study of how planets were perturbed by their moons, and in a paper read to the Academy on 27 November 1771 he made a study of the motions of the planets which would be the first step towards his later masterpiece on the stability of the solar system. Laplace's reputation steadily increased during the 1770s. It was the period in which he [1]:-
The 1780s were the period in which Laplace produced the depth of
results which have made him one of the most important and influential
scientists that the world has seen. It was not achieved, however,
with good relationships with his colleagues. Although d'Alembert
had been proud to have considered Laplace as his protégé,
he certainly began to feel that Laplace was rapidly making much
of his own life's work obsolete and this did nothing to improve
relations. Laplace tried to ease the pain for d'Alembert by stressing
the importance of d'Alembert's work since he undoubtedly felt well
disposed towards d'Alembert for the help and support he had given.
It was while Lexell was in Paris that Laplace made an excursion into a new area of science [2]:-
Although Laplace soon returned to his study of mathematical astronomy,
this work with Lavoisier marked the beginning of a third important
area of research for Laplace, namely his work in physics particularly
on the theory of heat which he worked on towards the end of his
career. Laplace served on many of the committees of the Académie des Sciences, for example Lagrange wrote to him in 1782 saying that work on his Traité de mécanique analytique was almost complete and a committee of the Académie des Sciences comprising of Laplace, Cousin, Legendre and Condorcet was set up to decide on publication. Laplace served on a committee set up to investigate the largest hospital in Paris and he used his expertise in probability to compare mortality rates at the hospital with those of other hospitals in France and elsewhere. Laplace was promoted to a senior position in the Académie des Sciences in 1785. Two years later Lagrange left Berlin to join Laplace as a member of the Académie des Sciences in Paris. Thus the two great mathematical geniuses came together in Paris and, despite a rivalry between them, each was to benefit greatly from the ideas flowing from the other. Laplace married on 15 May 1788. His wife, Marie-Charlotte de Courty de Romanges, was 20 years younger than the 39 year old Laplace. They had two children, their son Charles-Emile who was born in 1789 went on to a military career. Laplace was made a member of the committee of the Académie des Sciences to standardise weights and measures in May 1790. This committee worked on the metric system and advocated a decimal base. In 1793 the Reign of Terror commenced and the Académie des Sciences, along with the other learned societies, was suppressed on 8 August. The weights and measures commission was the only one allowed to continue but soon Laplace, together with Lavoisier, Borda, Coulomb, Brisson and Delambre were thrown off the commission since all those on the committee had to be worthy:-
Before the 1793 Reign of Terror Laplace together with his wife
and two children left Paris and lived 50 km southeast of Paris.
He did not return to Paris until after July 1794. Although Laplace
managed to avoid the fate of some of his colleagues during the Revolution,
such as Lavoisier who was guillotined in May 1794 while Laplace
was out of Paris, he did have some difficult times. He was consulted,
together with Lagrange and Laland, over the new calendar for the
Revolution. Laplace knew well that the proposed scheme did not really
work because the length of the proposed year did not fit with the
astronomical data. However he was wise enough not to try to overrule
political dogma with scientific facts. He also conformed, perhaps
more happily, to the decisions regarding the metric division of
angles into 100 subdivisions.
In 1795 the Académie des Sciences was reopened as the Institut National des Sciences et des Arts. Also in 1795 the Bureau des Longitudes was founded with Lagrange and Laplace as the mathematicians among its founding members and Laplace went on to lead the Bureau and the Paris Observatory. However although some considered he did a fine job in these posts others criticised him for being too theoretical. Delambre wrote some years later:-
Delambre also wrote concerning Laplace's leadership of the Bureau des Longitudes:-
Laplace presented his famous nebular hypothesis in 1796 in Exposition du systeme du monde, which viewed the solar system as originating from the contracting and cooling of a large, flattened, and slowly rotating cloud of incandescent gas. The Exposition consisted of five books: the first was on the apparent motions of the celestial bodies, the motion of the sea, and also atmospheric refraction; the second was on the actual motion of the celestial bodies; the third was on force and momentum; the fourth was on the theory of universal gravitation and included an account of the motion of the sea and the shape of the Earth; the final book gave an historical account of astronomy and included his famous nebular hypothesis. Laplace states his philosophy of science in the Exposition as follows:-
In view of modern theories of impacts of comets on the Earth it is particularly interesting to see Laplace's remarkably modern view of this:-
Exposition du systeme du monde was written as a non-mathematical
introduction to Laplace's most important work Traité du Mécanique
Céleste whose first volume appeared three years later. Laplace
had already discovered the invariability of planetary mean motions.
In 1786 he had proved that the eccentricities and inclinations of
planetary orbits to each other always remain small, constant, and
self-correcting. These and many other of his earlier results formed
the basis for his great work the Traité du Mécanique
Céleste published in 5 volumes, the first two in 1799.
In the Mécanique Céleste Laplace's equation appears
but although we now name this equation after Laplace, it was in
fact known before the time of Laplace. The Legendre functions also
appear here and were known for many years as the Laplace coefficients.
The Mécanique Céleste does not attribute many of the
ideas to the work of others but Laplace was heavily influenced by
Lagrange and by Legendre and used methods which they had developed
with few references to the originators of the ideas.
Laplace became Count of the Empire in 1806 and he was named a marquis
in 1817 after the restoration of the Bourbons. The first book studies generating functions and also approximations to various expressions occurring in probability theory. The second book contains Laplace's definition of probability, Bayes's rule (so named by Poincaré many years later), and remarks on moral and mathematical expectation. The book continues with methods of finding probabilities of compound events when the probabilities of their simple components are known, then a discussion of the method of least squares, Buffon's needle problem, and inverse probability. Applications to mortality, life expectancy and the length of marriages are given and finally Laplace looks at moral expectation and probability in legal matters. Later editions of the Théorie Analytique des Probabilités also contains supplements which consider applications of probability to: errors in observations; the determination of the masses of Jupiter, Saturn and Uranus; triangulation methods in surveying; and problems of geodesy in particular the determination of the meridian of France. Much of this work was done by Laplace between 1817 and 1819 and appears in the 1820 edition of the Théorie Analytique. A rather less impressive fourth supplement, which returns to the first topic of generating functions, appeared with the 1825 edition. This final supplement was presented to the Institute by Laplace, who was 76 years old by this time, and by his son. We mentioned briefly above Laplace's first work on physics in 1780 which was outside the area of mechanics in which he contributed so much. Around 1804 Laplace seems to have developed an approach to physics which would be highly influential for some years. This is best explained by Laplace himself:-
This approach to physics, attempting to explain everything from
the forces acting locally between molecules, already was used by
him in the fourth volume of the Mécanique Céleste
which appeared in 1805. This volume contains a study of pressure
and density, astronomical refraction, barometric pressure and the
transmission of gravity based on this new philosophy of physics.
It is worth remarking that it was a new approach, not because theories
of molecules were new, but rather because it was applied to a much
wider range of problems than any previous theory and, typically
of Laplace, it was much more mathematical than any previous theories.
After the publication of the fourth volume of the Mécanique Céleste, Laplace continued to apply his ideas of physics to other problems such as capillary action (1806-07), double refraction (1809), the velocity of sound (1816), the theory of heat, in particular the shape and rotation of the cooling Earth (1817-1820), and elastic fluids (1821). However during this period his dominant position in French science came to an end and others with different physical theories began to grow in importance. The Société d'Arcueil, after a few years of high activity, began to become less active with the meetings becoming less regular around 1812. The meetings ended completely the following year. Arago, who had been a staunch member of the Society, began to favour the wave theory of light as proposed by Fresnel around 1815 which was directly opposed to the corpuscular theory which Laplace supported and developed. Many of Laplace's other physical theories were attacked, for instance his caloric theory of heat was at odds with the work of Petit and of Fourier. However, Laplace did not concede that his physical theories were wrong and kept his belief in fluids of heat and light, writing papers on these topics when over 70 years of age. At the time that his influence was decreasing, personal tragedy struck Laplace. His only daughter, Sophie-Suzanne, had married the Marquis de Portes and she died in childbirth in 1813. The child, however, survived and it is through her that there are descendants of Laplace. Laplace's son, Charles-Emile, lived to the age of 85 but had no children. Laplace had always changed his views with the changing political events of the time, modifying his opinions to fit in with the frequent political changes which were typical of this period. This way of behaving added to his success in the 1790s and 1800s but certainly did nothing for his personal relations with his colleagues who saw his changes of views as merely attempts to win favour. In 1814 Laplace supported the restoration of the Bourbon monarchy and caste his vote in the Senate against Napoleon. The Hundred Days were an embarrassment to him the following year and he conveniently left Paris for the critical period. After this he remained a supporter of the Bourbon monarchy and became unpopular in political circles. When he refused to sign the document of the French Academy supporting freedom of the press in 1826, he lost the remaining friends he had in politics. On the morning of Monday 5 March 1827 Laplace died. Few events would cause the Academy to cancel a meeting but they did on that day as a mark of respect for one of the greatest scientists of all time. Surprisingly there was no quick decision to fill the place left vacant on his death and the decision of the Academy in October 1827 not to fill the vacant place for another 6 months did not result in an appointment at that stage, some further months elapsing before Puissant was elected as Laplace's successor. |