 The Avogadro constant is named after the early 19th @-@ century Italian scientist Amedeo Avogadro , who , in 1811 , first proposed that the volume of a gas ( at a given pressure and temperature ) is proportional to the number of atoms or molecules regardless of the nature of the gas . The French physicist Jean Perrin in 1909 proposed naming the constant in honor of Avogadro . Perrin won the 1926 Nobel Prize in Physics , largely for his work in determining the Avogadro constant by several different methods . 
