The French physical chemist Jean Baptiste Perrin, 1870-1942. Perrin studied in Lyons and Paris, and in 1910 became professor of physical chemistry at the Sorbonne. He investigated cathode rays, showing them to be negatively charged, and obtaining a rough value for their charge/mass ratio. He also studied the Brownian motion of particles in water. His results confirmed a mathematical analysis of the problem by Einstein, and enabled Perrin to give accurate values for Avogadro's constant and for the size of the water molecule. His work was widely accepted as final proof of the existence of atoms, and he was awarded the Nobel Prize for physics in 1926.