Laplace
Laplace, Pierre-Simon, Marquis de
ACHIEVEMENTS:
Probability theory
NICKNAME/ALIAS:
None
DATE AND PLACE OF BIRTH:
23 March 1749, Beaumont-en-Auge, Normandy, France
DATE AND PLACE OF DEATH AND AGE AT DEATH:
5 March 1827, Paris, France. Aged 78
DISCIPLINE:
Mathematician
FIELD:
Mathematics, astronomy
LANGUAGE:
French
PARENTS:
Father: Pierre Laplace
Mother: Marie-Anne Sochon
SIBLINGS:
1 sister: Marie-Anne
SPOUSE:
Marie Courty de Romange
CHILDREN:
1 son: Charles-Emile
1 daughter: Sophie-Suzanne
EDUCATION:
Military Academy, Beaumont-en-Auge
University of Caen
MAJOR WORK:
"Celestial Mechanics" (1799-1825)
"Analytic Theory of Probability" (1812)
LIFE AND TIMES:
When Laplace left Caen University for Paris his tutor gave him a letter of recommendation to the mathematician d'Alembert*. Within a few days he was appointed professor of mathematics at the Military Academy in Paris.
He immediately began his work on celestial mechanics with the aim of demonstrating the stability of the solar system in agreement with the Newtonian laws of motion. The planets of the solar system all exert gravitational pull on each other and on the sun, and Newton had said that occasional divine intervention was necessary to keep the entire
solar system stable.
Laplace focussed on the apparent irregularities in the motion of Jupiter and Saturn. (Jupiter's orbit appeared to be shrinking continuously while that of Saturn expanded continually). In 1773 Laplace proved that the mean distances of the planets from the Sun are invariable, with only slight periodic variations.
His discovery amounted to the most significant contribution to physical astronomy since Newton, and at the early age of twenty-four Laplace was appointed a member of the Academy of Sciences. In 1776 Laplace became involved in an argument with the Croatian astronomer and mathematician Boscovich* who was in Paris at the time.
Laplace was briefly diverted into working with the chemist Lavoisier* on a comparison of the application of quantitative methods to living and non-living systems. During the course of their investigations, they invented an ice calorimeter and in 1780 showed that respiration is a form of combustion.
Laplace then returned to applying mathematical theory to astronomy. In 1784-5 he was looking at the gravitational pull between spheroids, and proved that his theorem on
revolving spheroids applied to any spheroids with a common focus, and his investigations into the gravitational pull of masses on particles provided a mathematical basis for later investigations into heat and electromagnetism.
In 1786 he demonstrated that the differences between Jupiter and Saturn were periodic, not cumulative, and said that the gravitational movements of planetary orbits will always be small and periodic. There was no need for divine intervention because the planetary motions were also self-correcting.
The following year he provided an explanation for the apparent acceleration of the mean motion of the moon: it depended on the eccentricity of Earth's orbit, caused by the movements of other planets in the solar system. When Earth's orbit is more circular, the moon's mean motion is accelerated. Again, he showed that the effect is not cumulative, but periodic.
Laplace had removed the final objection to the stability of the solar system according to the Newtonian laws of gravitation He also made contributions to a theory of tidal movements. His method of tracing the orbits of comets was later replaced by that of Gauss*, the German mathematician.
In 1783 Laplace was appointed examiner of artillery cadets and two years' later examined Napoleon*. In 1793, he retired with his family to Melun, where he wrote a popular account of his celestial theory: "The System of the World" (1796). In the book, Laplace included a nebular hypothesis of the origin of the solar system, a concept earlier been touched on by the philosopher Kant* and which is sometimes referred to as the Kant-Laplacian theory.
In 1794 Laplace briefly taught mathematics in the newly established Ecole Normale, whose first students included Fourier*. In 1799 Laplace held office as Minister of the Interior for a short period.
Publication of his major five-volume work, "Celestial Mechanics", began in the same year. It became one of the most influential books on astronomy and mathematics, affecting the work of all leading astronomers who followed on from Laplace, including JWF Herschel* and Airy*.
Laplace was one of the leaders of the Arcueil circle of scientists, including Poisson* and Gay-Lussac*.
During his work on the planets, Laplace had applied a theory of probability to his calculations about the planets and their movements over a period of time. The wider application of probability theory had been urged by Condorcet*. In the seventeenth century, Jakob Bernoulli* in Switzerland and the French mathematician de Moivre* had made advances to probability Theory, while in the eighteenth century the English mathematician Bayes* had investigated inductive probability. In 1812 Laplace published his "Analytical Theory of Probability" in which he showed the application of the theory to a number of subjects outside physics and astronomy.
In 1814 he published a popular version of his theory in: "A Philosphical Essay on Probability".
After the fall of Napoleon, Laplace transferred his allegiance to Louis XVIII, and was made a marquis. In 1817 Laplace became president of the French Academy. He was a prominent member of the scientific community and treated as a celebrity.
His support of Fourier's analytic theory of heat helped to overcome the objections of Poisson and Biot*. In 1822 Laplace received Quetelet*, the Belgian mathematician astronomer, who was profoundly influenced by Laplace's "Celestial Mechanics".
ASSESSMENT: Remembered for his mathematical work in astronomy.
EXTRA CONNECTIONS: Met Brewster* and Somerville*
Ferrel* questioned his tide theories.
He knew Venturi*
He acknowledge the quality of the earth-density calcuations of Charles Hutton*
He helped develop the metric system*
ONELINER: Pierre-Simon Laplace, great French mathematician
BIBLIOGRAPHY:
Crosland, Maurice, The Society of Arcueil, Heinemann, London, 1967
Bell, ET, Men of Mathematics, Victor Gollancz Ltd., London, 1937