the constant, random, zigzag movements of small particles dispersed in a fluidmedium, caused by collision with molecules of the fluid. First observed by Scottish botanist Dr. Robert Brown (1773 - 1858) in examination, under a microscope, of liquids containing very small particles which were just large enough to be visible. —Webster's New World Dictionary, Second College Edition and Collier's Encyclopedia (5th ACC Glossary Part 1) Final approval 2.12.89