(Lorenzo Romano) Amedeo (Carlo) Avogadro, the Italian physicist (1776-1856). Although trained in law, after 1800 he turned to science and held professorships in physics for much of his life. His fame now rests on one brilliant and important idea. He considered Gay-Lussac's law of combining volumes in gases and with little evidence offered a daring explanation of it in 1811. His idea, Avogadro's law, was that equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of particles (the particles being atoms or molecules depending on the nature of the gas being considered).