Fr.: mouvement brownien
The continuous random motion of solid microscopic particles immersed in a fluid due to bombardment by the atoms and molecules of the medium. The first quantitative explanation of the phenomenon, based on the kinetic theory of gases, was forwarded by A. Einstein in 1905.
Named after Robert Brown (1773-1858), a Scottish botanist, who first in 1827 noticed the erratic motion of pollen grains suspended in water. → motion.