Amedio Avogadro (1776-1856) worked as a lawyer before taking up science and becoming professor of physics. In about 1811, he imagined a row of the same-sized containers. Each held a different gas, but at the same numbers of molecules in each container. This is now known as Avogadro’s law-equal volumes of all gase, when at the same temperatures and pressure, have the same numbers of atoms or molecules.