The English botanist Robert Brown is credited for the discovery of Brownian motion. This phenomenon pertains to the erratic motion of microscopic particles that are suspended in a liquid or gaseous substance. The movement is due to the rapid movement of molecules that comprise the fluid.
Brown conducted an experiment in 1827 where he used small grains of pollen suspended in water. Using a microscope, he observed that the pollen grains produced a jittery motion. Although the water was completely still, Brown noted that the grains moved in an unpredictable manner. However, Brown was unable to deduce the cause of the movement. It wasn't until Albert Einstein published his findings in 1905 that a thorough explanation of Brownian motion became available to the public.