Laplace persuaded him to renounce engineering and
to devote himself to mathematics. He obtained an appointment at the
Ecole Polytechnique, which, however, he relinquished in 1830 on the
accession of Louis Philippe, finding it impossible to take the necessary
oaths. A short sojourn at Freiburg in Switzerland was followed by his
appointment in 1831 to the newly-created chair of mathematical physics
at the university of Turin. In 1833 the deposed king Charles X. summoned
him to be tutor to his grandson, the duke of Bordeaux, an appointment
which enabled Cauchy to travel and thereby become acquainted with the
favourable impression which his investigations had made. Charles created
him a baron in return for his services. Returning to Paris in 1838, he
refused a proffered chair at the College de France, but in 1848, the
oath having been suspended, he resumed his post at the Ecole
Polytechnique, and when the oath was reinstituted after the _coup
d'etat_ of 1851, Cauchy and Arago were exempted from it. A profound
mathematician, Cauchy exercised by his perspicuous and rigorous methods
a great influence over his contemporaries and successors. His writings
cover the entire range of mathematics and mathematical physics.

Cauchy had two brothers: ALEXANDRE LAURENT (1792-1857), who became a
president of a division of the court of appeal in 1847, and a judge of
the court of cassation in 1849; and EUGENE FRANCOIS (1802-1877), a
publicist who also wrote several mathematical works.

The genius of Cauchy was promised in his simple solution of the
problem of Apollonius, i.e. to describe a circle touching three given
circles, which he discovered in 1805, his generalization of Euler's
theorem on polyhedra in 1811, and in several other elegant problems.
More important is his memoir on wave-propagation which obtained the
_Grand Prix_ of the Institut in 1816. His greatest contributions to
mathematical science are enveloped in the rigorous methods which he
introduced. These are mainly embodied in his three great treatises,
_Cours d'analyse de l'Ecole Polytechnique_ (1821); _Le Calcul
infinitesimal_ (1823); _Lecons sur les applications du calcul
infinitesimal a la geometrie_ (1826-1828); and also in his courses of
mechanics (for the Ecole Polytechnique), higher algebra (for the
Faculte des Sciences), and of mathematical physics (for the College de
France). His treatises and contributions to scientific journals (to