Alexis Petit was a French physicist. He and his brother-in-law, Francois Arago, worked on the refraction of light in gases and eventually accepted Augustin Fresnel's new wave theory of light. In 1818, Petit and Pierre Dulong won a prize for determining the specific heat capacity of solids and for devising measurements of temperature, research that led the following year to Dulong and Petit's law.