Amedeo Avogadro. Portrait of Lorenzo Romano Amedeo Carlo Avogadro (1776-1856), Conte di Quaragne e Ceretto, Italian physicist and chemist. Although trained in law, after 1800 he turned to science and held professorships in physics for much of his life. Avogadro worked on thermodynamics, electricity and the properties of liquids. His major contribution to science was his explanation of Gay-Lussac's law of combining volumes in gases. Avogadro stated that equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of particles. This hypothesis, Avogadro's Law, was not widely accepted until after his death.