Avogadro, Amedeo (1776-1856), an Italian physicist and chemist. His research in molecular structure was one of the early steps leading to modern atomic theory. In 1811 he published the important hypothesis, now known as Avogadro's Law, that under the same conditions of temperature and pressure, equal volumes of all gases contain the same number of molecules.

Avogadro was born in Turin. He was a professor of mathematical physics at the University of Turin, 1834-50.