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Essay on Pierre Simon Laplace
Laplace worked on probability, chemistry and astronomy, and the Laplacian is named after him, though it had appeared before his grand work. Laplace's great work was done in raising the mathematical scrutiny of the system of gravitational astronomy worked out by Sir Isaac Newton, English mathematician, physicist, and astronomer. Laplace proved that planetary motions are stable, and that perturbations produced by reciprocal power of planets or by external bodies, such as comets, are only temporary. He attempted to give a balanced theory of the origin of the solar system in his nebular hypothesis of stellar evolution. In Traité de mécanique céleste Treatise on Celestial Mechanics, 5 volumes, and 1799-1825) Laplace systematized all the mathematical work that had been done on gravitation. Exposition du système du monde (Explanation of the World System, 1796) contained a summary of the history of astronomy.
Laplace's original significant breakthrough came soon after he was selected for the Ecole Militaire. He revealed that 'any determinant is equal to the sum of all the minors that can be formed from any selected set of its rows, each minor being described by its algebraic balance'. This is what is now known as the Laplace theorem. He then turned his mind to problems in celestial mechanics, beginning in 1773 by examining the unsolved variations in the orbits of Jupiter and Saturn. Jupiter's orbit appeared to be continually shrinking, at the same time as Saturn's appeared to be persistently growing. No one had succeeded in explaining the observable fact within the structure of Newtonian gravitation. In a luminous three-part paper presented to the academy 1784-86, Laplace verified that the phenomenon had a period of 929 years and that arose for the reason that the average motions of the two planets are nearly commensurable. The variations, therefore, were not at odds with, but compatible with, Isaac Newton's law....
