Brownian Movement

The contin­uous random movement of micro­scopic solid particles (of about 1 micrometre in diameter) when sus­pended in a fluid medium. First observed by the British botanist Robert Brown (1773-1858) in 1827 when studying pollen particles, it was origi­nally thought to be the manifestation of some vital force. It was later recog­nized to be a consequence of bom­bardment of the particles by the continually moving molecules of the liquid. The smaller the particles the more extensive is the motion. The ef­fect is also visible in particles of smoke suspended in a still gas.