This is, presumably the random drifting of particles suspended in a fluid (a liquid or a gas) .This movement was discovered and later named after botanist Robert Brown (1773-1858). He was a Scottish botanist and palaeobotanist who made important contributions (including Brownian motion) to botany largely through his pioneering use of the microscope. The scientist who made Brownian motion famous is Albert Einstein, who brought the phenomenon to the attention of the larger physics community by publishing a paper on it in 1905, his personal annus mirabilis or "wonderful year."
The phenomenon was observed as early as 1765, but not described or studied in detail until the botanist Robert Brown's research in 1827. Brownian motion is named in honor of his work. As a botanist, Brown first observed the effect in pollen floating in water, where it is visible with the naked eye. Through experimentation, Brown determined that the specks of pollen were not propelling themselves independently, but rather that their motion was pseudo-random.
Jean Perrin, a French physicist who later won the Nobel prize, spring boarded off of Einstein's work. Using Brownian motion as evidence, he proved in 1911, once and for all, that matter is made of atoms and molecules.
Diffusion, also called molecular diffusion, is the process by which molecules of a given substance move from an area of relatively high concentration to an area of lower concentration. When the molecules have diffused so that they are in a uniform concentration, this state is called equilibrium. This phenomenon plays a key role in many disciplines of biology, physics, and chemistry. It is closely related to the way in which cells take up nutrients, thus life could not exist without it. Regardless of the state of matter that a group of molecules finds itself in, all the molecules are moving to some degree. They not only move, but they do so randomly, in no particular pattern. This...