1870-1942

French physicist awarded the 1926 Nobel Prize in physics for his work on Brownian motion. In 1895 he settled the cathode ray particle-wave debate by demonstrating that cathode rays carry negative charges and are thus particles. Perrin's classic studies of Brownian motion (1908) provided the first demonstration of the existence of atoms. He confirmed Einstein's mathematical analysis of Brownian motion. This enabled Perrin to accurately calculate Avogadro's number and derive the size of water molecules.