Avogadro, Amedeo, ah vuh GAH droh, ah mah DEE oh (1776-1856), was an Italian physicist. He proposed in 1811 his famous hypothesis, now known as Avogadro's law. The law stated that equal volumes of all gases at the same temperature and pressure contain the same number of chemical units. Avogadro distinguished between gases composed of complex units (molecules) and gases made up of simple units (atoms). He was able to calculate from gas densities the amount of matter in atoms and molecules (see Atom). Avogadro's hypothesis was not accepted by the leading scientists of his time. His hypothesis was discounted until 1858, when Italian chemist Stanislao Cannizzaro reintroduced it and developed it further. Avogadro was born in Turin, Italy, on Aug. 9, 1776. He died on July 9, 1856. See also Chemistry.