Augustin Cauchy

Born the son of a senior civil servant of the ancien régime just one month after the storming of the Bastille, Augustin-Louis Cauchy was to remain influenced by the French Revolution and the political turmoil it unleashed throughout Europe. He grew up in the religious atmosphere of a very pious Catholic family in the village of Arcueil, where they were able to remain hidden from revolutionary attacks and the young Cauchy was taught the classical subjects admirably by his father. Later, he studied at the École Polytechique and École des Ponts et Chaussées (1805–09). It is alleged that as Cauchy was en route from Paris to Cherbourg in order to assist in the building of the naval harbour (1810–13), he carried with him Mécanique céleste (Pierre Simon Laplace, 1749–1827) and Traité des fonctions analytiques (Joseph Louis Lagrange, 1736–1813), among other works. At the start of his structural engineering activities he sent two essays on masonry arch theory to Gaspard Prony (1755–1839) in Paris [Cauchy, 1809 & 1810], but the latter lost them and they were never published. Before his return to Paris in 1813, Cauchy turned more and more to mathematics; he is supposedly one of the most productive mathematicians ever to have lived [Novy, 1978]. His influential father tried to use his official position to secure his highly talented son vacant posts in the Académie des Sciences (1813 and 1814), but without success. It was not until the restoration of the Bourbon monarchy and the expulsion of revolutionary sympathisers among the scientists at the Académie – such as Lazare Carnot and Gaspard Monge – that Cauchy was offered a post at, but not elected to, the Académie (1816). He never disputed the fact that he was the successor to the expelled Monge. That launched Cauchy’s career, which was initially interrupted by the July Revolution of 1830 because he refused to declare allegiance to the Orleanist Louis Philippe (“King of the French”) and instead followed the overthrown Bourbon King Charles X into exile. Cauchy was professor at tehCauchy was offered a post at, but not elected to, the Académie (1816). He never disputed the fact that he was the successor to the expelled Monge. That launched Cauchy’s career, which was initially interrupted by the July Revolution of 1830 because he refused to declare allegiance to the Orleanist Louis Philippe (“King of the French”) and instead followed the overthrown Bourbon King Charles X into exile. Cauchy was professor at the Cauchy was offered a post at, but not elected to, the Académie (1816). He never disputed the fact that he was the successor to the expelled Monge. That launched Cauchy’s career, which was initially interrupted by the July Revolution of 1830 because he refused to declare allegiance to the Orleanist Louis Philippe (“King of the French”) and instead followed the overthrown Bourbon King Charles X into exile. Cauchy was professor at the École polytechnique and the Sorbonne as well as a member of the Collège de France. Encouraged by Laplace and Poisson, Cauchy wrote Cours d‘Analyse de l’École Polytechnique, which became a work that placed differential and integral calculus on a new footing by assuming a precisely defined consistent concept of the infinitesimal, which formed the framework for his mechanics based on the continuum hypothesis in the early 1820s. In his work Recherches sur l’équilibre et le mouvement intérieur des corps solides ou fluides, élastiques ou non élastiques [Cauchy, 1823], presented to the Académie in 1822 and published in 1823, Cauchy explains continuum mechanics and presents a valid definition of the stress concept Sorbonne as well as a member of the Collège de France. Encouraged by Laplace and Poisson, Cauchy wrote Cours d‘Analyse de l’École Polytechnique, which became a work that placed differential and integral calculus on a new footing by assuming a precisely defined consistent concept of the infinitesimal, which formed the framework for his mechanics based on the continuum hypothesis in the early 1820s. In his work Recherches sur l’équilibre et le mouvement intérieur des corps solides ou fluides, élastiques ou non élastiques [Cauchy, 1823], presented to the Académie in 1822 and published in 1823, Cauchy explains continuum mechanics and presents a valid definition of the stress concept Sorbonne as well as a member of the Collège de France. Encouraged by Laplace and Poisson, Cauchy wrote Cours d‘Analyse de l’École Polytechnique, which became a work that placed differential and integral calculus on a new footing by assuming a precisely defined consistent concept of the infinitesimal, which formed the framework for his mechanics based on the continuum hypothesis in the early 1820s. In his work Recherches sur l’équilibre et le mouvement intérieur des corps solides ou fluides, élastiques ou non élastiques [Cauchy, 1823], presented to the Académie in 1822 and published in 1823, Cauchy explains continuum mechanics and presents a valid definition of the stress concept in extraordinarily clear language without resorting to equations [Cauchy, 1823, p. 10]. He introduced the stress tensor [Cauchy, 1827/1] and the strain tensor [Cauchy, 1827/2] in 1827. He generalised the Hookean law in 1828/29, which enabled him to generate the set of equations for elastic theory based on the molecular hypothesis in the (implicit) mathematical form of tensor calculus [Herbert, 1991]. It was not until 1837 that George Green was able to prove with the help of the law of conservation of energy that a consistent elastic theory for isotropic materials requires two elasticity constants and not just one, as would result from the molecular hypothesis [Green, 1839]. Cauchy returned to France at the end of 1838 and one year later was elected to the Bureau of Longitude. It was only after the oath of allegiance was abolished by the February Revolution of 1848 that Cauchy was able to take up his academic functions again without having to deviate from his active clericalism. The Catholic Church used his devotion as an example of the reconcilability of faith and science. As Cauchy fell ill in May 1857, clerics gathered around his deathbed and the Cardinal of Paris administered the last rites.

Main contributions to structural analysis:

Mémoire sur les ponts en pierre, par A. L. Cauchy, élève des Ponts et Chaussées [1809]; Second mémoire sur les ponts en pierre, théorie des voûtes en berceau, par A. L. Cauchy, élève des Ponts et Chaussées [1810]; Recherches sur l’équilibre et le mouvement intérieur des corps solides ou fluides, élastiques ou non élastiques [1823]; De la pression ou tension dans un corps solide [1827/1]; Sur la condensation et la dilatation des corps solides [1827/2]

Source: Kurrer, Karl-Eugen The History of the Theory of Structures, Wilhelm Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH, Berlin (Deutschland), ISBN 3-433-01838-3, 2008; p. 721