A lawyer by trade, Avogadro's first scientific research in 1803 was on electricity. He was appointed demonstrator at the Academy of Turin in 1806. In 1811 Avogadro explained Gay-Lussac's Law (gases combine in volume ratios of small integers) by proposing that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. This became known as Avogadro's Law. He made the distinction between atoms and molecules, and his work eventually spawned the concept of molar mass. (Avogadro's number wasn't determined until well after his death in 1856.)