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 WorldDictionary, SecondCollege Edition and Collier's Encyclopedia (5th ACC Glossary Part 1) Final approval 2.12.89