Biography

 

Admitted to Ecole des Ponts in 1776, he left in 1779 to work in Bourges, Argenton, Dourdan, Lagny and Paris.He notably headed construction work on Pont de la Concorde and Pont de Pont-Sainte-Maxence on the River Oise, both supervised by Perronet.Appointed chief engineer in Perpignan in 1791, he succeeded in becoming director of the Land Registry in order to remain in Paris.At the same time, he undertook the writing of logarithmic tables to fourteen, nineteen, twenty-five and twenty-nine decimal places, still extant in manuscript form (at the Observatoire de Paris, the Institut de France and Ecole des Ponts et Chaussées), for use in astronomical calculations, described as the “largest and most imposing monument to calculation ever produced or even conceived” (18 volumes).This achievement includes, on the one hand, the logarithms from 1 to 200,000, the first 10,000 numbers calculated to 19 decimal places and the rest to 14, with six columns of differences; and on the other, 200,000 plus a few thousand logarithms of trigonometric rows, more precisely 10,000 natural number sines calculated to 29 and 25 decimal places, with seven or eight columns of differences; 200,000 logarithms, both  sine and tangent, calculated to 14 decimal places, with six columns of differences; and finally 10,000 logarithms on the relations between sines and arc tangents, to facilitate interpolation in calculations relating to small angles, to 14 decimal places as before, with six columns of differences.

On Perronet’s death, it was Jacques-Élie Lamblardie who took charge of École des ponts et chaussées.Prony took advantage of this to work with Monge in the establishment of the Ecole Polytechnique, notably heading the course on mechanics.Charged by Napoleon with assignments in Italy, Prony travelled there three times:the first in 1805, to inspect the course of the River Po and to carry out work in the Port of Genoa and the Gulf of Spezzia (where he was arrested in Venice and accused of espionage by the Austrian police); the second in 1806, to improve the ports of Ancona, Venice and Pola; and the third in 1810 and 1811, to clean up the region occupied by the pontine marshes.In 1798, Prony succeeded Lamblardie at the head of École des ponts et chaussées, where he remained for 41 years until his death.In this role, he broke with the pragmatism of Perronet and the old pedagogy based on “self-teaching” (an ill-defined teaching programme arbitrarily delivered by the best students):he introduced a lecture system, created teaching professorships and structured the organisation of scientific education.In other words, he laid the foundations for the modern School.In 1835, he became a baron and was named a peer of France.Gaspard de Prony was also a member of most of Europe’s great academies, and explored many scientific fields:in 1832, he published a treatise on musical intervals and created an interval unit that bears his name, the prony.He also developed a dynamometric braking mechanism for steam engines, called the Prony brake, which was used in a test in Paris at the Gros-Caillou on a water supply system to the left bank districts.

His name is inscribed on the Eiffel Tower frieze.

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