Alexis Thérèse Petit

Alexis Thérèse Petit ( born October 2, 1791 in Vesoul, † June 21, 1820 in Paris) was a French physicist.


He attended the École Centrale in Besançon with great success. Switched to a private school in Paris, where he was taught by teachers who had originally received their training at the École Polytechnique. At the age of ten, so in 1801 was A.T. Petit already qualified enough to be accepted as a student at the École Polytechnique in Paris. Nevertheless, the formal entry requirements were designed so that it could only be taken with 16 years. He therefore had to wait for about five years before he was accepted. He attended at the École in 1807, the same class as the French mathematician, engineer and physicist Jean -Victor Poncelet ( 1788-1867 ), who was almost three years older than Petit. He received his doctorate in 1811 for an outstanding dissertation via capillary action, Théorie de l' Action Mathématique Capillaire. Petit who studied at the École Polytechnique, where he later became followers of Pierre- Simon Laplace (1749-1827) the French mathematician and physicist, in his capacity as a professor of physics.

Petit married one of the sisters of Dominique François Jean Arago ( 1786-1853 ). His brother was also a physicist but also politicians. His young wife died in 1817 of tuberculosis. Furthermore, it is to report that both Pierre Louis Dulong and Dominique François Jean Arago from July 1807 in the Mémoires de Physique et de Chimie de la Société d' Arcueil, were mentioned as a member of the Société d' Arcueil, a circle of scientists.

The lunar crater Petit was named after him in 1976.

Scientific achievements

A.T. Petit and François Arago experimented together, for example through the refraction of light in gases. In particular, they investigated the influence of temperature on the refractive index of gases. As A.T. Petit studied at the École Polytechnique physics was taught that light was composed of corpuscles. However, its joint work with the brother François Arago in 1815, it gave a different view of the nature of light, and in December of the same year he became an outspoken representative of the wave theory of light.

In 1819 he formulated together with Pierre Louis Dulong ( 1785-1838 ), the Dulong - Petit law.


  • Petit, A. T.; Dulong, PL: Recherches sur quelques points importants de la théorie de la chaleur. In: Annales de Chimie et de Physique. Vol 10, 1819, pp. 395-413.