Amedeo Avogadro publishes in 1811, in the Journal de Physique, the hypothesis that equal volumes of different gases, at the same temperature and pressure, contain the same number of molecules. With this he reconciles Dalton's atomic theory with Gay-Lussac's observations on gas combination ratios, by introducing a crucial distinction between atom and molecule: elemental gases are not loose atoms but molecules of two or more atoms (for example, oxygen as O2). The hypothesis was practically ignored for almost fifty years — partly due to the lack of solid experimental data in Avogadro's own paper, partly due to rejection by influential figures such as Berzelius — until Stanislao Cannizzaro rescued it in 1858 as the basis of a coherent system of atomic weights.