Pierre-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:-

There is little record of intellectual distinction in the family beyond what was to be expected of the cultivated provincial bourgeoisie and the minor gentry.

*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.
Once he knew that mathematics was to be his subject, Laplace left
Caen without taking his degree, and went to Paris. He took with
him a letter of introduction to d'Alembert from Le Canu, his teacher
at Caen. Although Laplace was only 19 years old when he arrived
in Paris he quickly impressed d'Alembert. Not only did d'Alembert
begin to direct Laplace's mathematical studies, he also tried to
find him a position to earn enough money to support himself in Paris.
Finding a position for such a talented young man did not prove hard,
and Laplace was soon appointed as professor of mathematics at the
Ecole Militaire. Gillespie writes in [1]:-*

Imparting geometry, trigonometry, elementary analysis, and statics to adolescent cadets of good family, average attainment, and no commitment to the subjects afforded little stimulus, but the post did permit Laplace to stay in Paris.

*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.
Laplace's first paper which was to appear in print was one on the
integral calculus which he translated into Latin and published at
Leipzig in the Nova acta eruditorum in 1771. Six years later Laplace
republished an improved version, apologising for the 1771 paper
and blaming errors contained in it on the printer. Laplace also
translated the paper on maxima and minima into Latin and published
it in the Nova acta eruditorum in 1774. Also in 1771 Laplace sent
another paper Recherches sur le calcul intégral aux différences
infiniment petites, et aux différences finies to the Mélanges
de Turin. This paper contained equations which Laplace stated were
important in mechanics and physical astronomy. *

*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]:-*

... established his style, reputation, philosophical position, certain mathematical techniques, and a programme of research in two areas, probability and celestial mechanics, in which he worked mathematically for the rest of his life.

*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 does appear that Laplace was not modest about his abilities and
achievements, and he probably failed to recognise the effect of
his attitude on his colleagues. Lexell visited the Académie
des Sciences in Paris in 1780-81 and reported that Laplace let it
be known widely that he considered himself the best mathematician
in France. The effect on his colleagues would have been only mildly
eased by the fact that Laplace was right! Laplace had a wide knowledge
of all sciences and dominated all discussions in the Academy. As
Lexell wrote:- *

... in the Academy he wanted to pronounce on everything.

*It was while Lexell was in Paris that Laplace made an excursion
into a new area of science [2]:-*

Applying quantitative methods to a comparison of living and nonliving systems, Laplace and the chemist Antoine Lavoisier in 1780, with the aid of an ice calorimeter that they had invented, showed respiration to be a form of combustion.

*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.
In 1784 Laplace was appointed as examiner at the Royal Artillery
Corps, and in this role in 1785, he examined and passed the 16 year
old Napoleon Bonaparte. In fact this position gave Laplace much
work in writing reports on the cadets that he examined but the rewards
were that he became well known to the ministers of the government
and others in positions of power in France. *

*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:- *

... by their Republican virtues and hatred of kings.

*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 Ecole Normale was founded with the aim of training school
teachers and Laplace taught courses there including one on probability
which he gave in 1795. The Ecole Normale survived for only four
months for the 1200 pupils, who were training to become school teachers,
found the level of teaching well beyond them. This is entirely understandable.
Later Laplace wrote up the lectures of his course at the Ecole Normale
as Essai philosophique sur les probabilités published in
1814. A review of the Essai states:- *

... after a general introduction concerning the principles of probability theory, one finds a discussion of a host of applications, including those to games of chance, natural philosophy, the moral sciences, testimony, judicial decisions and mortality.

*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:- *

... never should one put a geometer at the head of an observatory; he will neglect all the observations except those needed for his formulas.

*Delambre also wrote concerning Laplace's leadership of the Bureau
des Longitudes:- *

One can reproach [Laplace] with the fact that in more than 20 years of existence the Bureau des Longitudes has not determined the position of a single star, or undertaken the preparation of the smallest catalogue.

* 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:-
*

If man were restricted to collecting facts the sciences were only a sterile nomenclature and he would never have known the great laws of nature. It is in comparing the phenomena with each other, in seeking to grasp their relationships, that he is led to discover these laws...

*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:- *

... the small probability of collision of the Earth and a comet can become very great in adding over a long sequence of centuries. It is easy to picture the effects of this impact on the Earth. The axis and the motion of rotation have changed, the seas abandoning their old position..., a large part of men and animals drowned in this universal deluge, or destroyed by the violent tremor imparted to the terrestrial globe.

*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.
The first volume of the Mécanique Céleste is divided
into two books, the first on general laws of equilibrium and motion
of solids and also fluids, while the second book is on the law of
universal gravitation and the motions of the centres of gravity
of the bodies in the solar system. The main mathematical approach
here is the setting up of differential equations and solving them
to describe the resulting motions. The second volume deals with
mechanics applied to a study of the planets. In it Laplace included
a study of the shape of the Earth which included a discussion of
data obtained from several different expeditions, and Laplace applied
his theory of errors to the results. Another topic studied here
by Laplace was the theory of the tides but Airy, giving his own
results nearly 50 years later, wrote:- *

It would be useless to offer this theory in the same shape in which Laplace has given it; for that part of the Mécanique Céleste which contains the theory of tides is perhaps on the whole more obscure than any other part...

*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.
Under Napoleon Laplace was a member, then chancellor, of the Senate,
and received the Legion of Honour in 1805. However Napoleon, in
his memoirs written on St Hélène, says he removed
Laplace from the office of Minister of the Interior, which he held
in 1799, after only six weeks:- *

... because he brought the spirit of the infinitely small into the government.

*Laplace became Count of the Empire in 1806 and he was named a marquis
in 1817 after the restoration of the Bourbons.
The first edition of Laplace's Théorie Analytique des Probabilités
was published in 1812. This first edition was dedicated to Napoleon-le-Grand
but, for obvious reason, the dedication was removed in later editions!
The work consisted of two books and a second edition two years later
saw an increase in the material by about an extra 30 per cent. *

*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:- *

... I have sought to establish that the phenomena of nature can be reduced in the last analysis to actions at a distance between molecule and molecule, and that the consideration of these actions must serve as the basis of the mathematical theory of these phenomena.

*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.
Laplace's desire to take a leading role in physics led him to become
a founder member of the Société d'Arcueil in around
1805. Together with the chemist Berthollet, he set up the Society
which operated out of their homes in Arcueil which was south of
Paris. Among the mathematicians who were members of this active
group of scientists were Biot and Poisson. The group strongly advocated
a mathematical approach to science with Laplace playing the leading
role. This marks the height of Laplace's influence, dominant also
in the Institute and having a powerful influence on the Ecole Polytechnique
and the courses that the students studied there. *

*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. *