Named after the Scottish botanist Robert Brown who discovered it among pollen grains on water during his studies of plant sexual behaviour. Tiny particles suspended in fluid, such as dust in cigarette smoke or Brown's pollen grains, when and seen through microscope, are in a constant state of random motion. The phenomenon occurs because the particles are so small that they visibly move on collision with molecules of fluid. This is evidence that molecules themselves are in constant random motion. Also called "Brownian movement." 


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