Alexis Thérèse Petit

Alexis Thérèse Petit was born in Vesoul, France, in 1791. A precocious student, he is said to have qualified for entry to the École Polytechnique at an exceptionally young age, and he graduated at the top of his class. By his mid-twenties he held the chair of physics at the École Polytechnique, a remarkable ascent.

Petit's early work, some of it with the young Dominique François Jean Arago, examined the refractive indices of gases and questions in optics and the theory of heat. He was an advocate of the wave theory of light at a time when the corpuscular theory still held sway in France.

His lasting fame rests on the 1819 collaboration with Pierre Louis Dulong on the specific heats of solids, which produced the Dulong–Petit law: the molar heat capacity of simple solids is nearly constant. The result became a tool for determining atomic weights and, much later, a benchmark that classical and then quantum theories of solids had to explain.

Petit's career was cut tragically short. He contracted tuberculosis and died in Paris in 1820 at the age of twenty-nine, only months after the publication of the work that secured his name in the history of physics.