AVOGADRO, AMEDEO, CONTE DI QUAREGNA (1776 1856), Italian physicist, was born at Turin on June 9 1776, and died there on July 9 1856. He was for many years professor of higher physics in Turin University. He is chiefly remembered for his "Essai d'une maniere de determiner les masses relatives des molecules elementaires des corps, et les proportions selon les quelles elles entrent dans les combinaisons" Clown. de Phys., 1811), in which he enunciated the hypothesis known by his name (Avogadro's law) that under the same conditions of tem perature and pressure equal volumes of all gases contain the same number of smallest particles or molecules, whether those particles consist of single atoms or are composed of two or more atoms of the same or different kinds.