Alexis Thérèse Petit was a French

France

The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 physicist

Physicist

A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...

. Petit is known for his work on the efficiencies of air- and steam-engines, published in 1818. His well-known discussions with the French physicist Sadi Carnot

Nicolas Léonard Sadi Carnot

Nicolas Léonard Sadi Carnot was a French military engineer who, in his 1824 Reflections on the Motive Power of Fire, gave the first successful theoretical account of heat engines, now known as the Carnot cycle, thereby laying the foundations of the second law of thermodynamics...

, founder of thermodynamics

Thermodynamics

Thermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...

, may have stimulated Carnot in the development theories of thermodynamic efficiency in heat engine

Heat engine

In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

s.

Petit was born in Vesoul

Vesoul

Vesoul is a commune in the Haute-Saône department in the region of Franche-Comté in eastern France.The town is the capital of the department, its inhabitants are known in French as Vésuliens.-Notable people:...

, Haute-Saône

Haute-Saône

Haute-Saône is a French department of the Franche-Comté région, named after the Saône River.- History :The department was created in the early years of the French Revolution through the application of a law dated 22 December 1789, from part of the former province of Franche-Comté...

. He is best known for the Dulong-Petit law for the specific heat capacity of metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s, which he co-discovered with Pierre Louis Dulong

Pierre Louis Dulong

Pierre Louis Dulong was a French physicist and chemist, remembered today largely for the law of Dulong and Petit. He worked on the specific heat capacity and the expansion and refractive indices of gases....

in 1819.