Amedeo Avogadro did not discover or name "Avogadro 's number". He did however play a major role into the discovery of that number. In 1811 he proposed the hypothesis that the "equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties". Many scientists after that used his hypothesis to try and calculate the number of molecules in a mole, Josef Loschmidt being one of those scientists. Josef Loschmidt greatly contributed towards the discovery of Avogadro 's number by being the first scientist to come up with a number, although it wasn 't 100% correct. The person who finally discovered the number that we used today it Jean Perrin. He is the