Robert Brown (botanist) - Brownian Motion

Brownian Motion

In 1827, while examining grains of pollen of the plant Clarkia pulchella suspended in water under a microscope, Brown observed minute particles, now known to be amyloplasts (starch organelles) and spherosomes (lipid organelles), ejected from the pollen grains, executing a continuous jittery motion. He then observed the same motion in particles of inorganic matter, enabling him to rule out the hypothesis that the effect was life-related. Although Brown did not provide a theory to explain the motion, and Jan Ingenhousz already had reported a similar effect using charcoal particles, in German and French publications of 1784 and 1785, the phenomenon is now known as Brownian motion.

In recent years it was generally held that Brown's microscopes were insufficient to reveal phenomena of this order. Brown's re-discoveries were denied in a brief paper in 1991. Shortly thereafter, in a hastily-compiled illustrated presentation, British microscopist Brian J. Ford presented to Inter Micro 1991 in Chicago a reprise of the demonstration. His video sequences substantiated Brown's observations. Physicist Phil Pearle and colleagues presented a detailed discussion of Brown's original observations of particles from pollen of Clarkia pulchella undergoing Brownian motion, including the relevant history, botany, microscopy, and physics.