Brownian Motion
Properties of Matter

Brownian motion: facts and myths

Teaching Guidance for 14-16 PRACTICAL PHYISCS

Robert Brown is correctly referred to as having observed the jittering motion of small particles. But he did not observe the motion of actual pollen grains. How many text books and other resources continue to hand on this mistake?

A 2001 paper published in Nature alleged that the first recorded observation of what we now call Brownian motion was made in 1785 by Jan Ingenhousz using charcoal dust [Ref: Nature, 7 June 2001 p 641]. This appears not to be the case. See the Microscopy website...


The webpage may also be of interest for its two short videos showing Brownian motion, one in whole milk and the other in a smoke cell.

Having used particles derived from living matter, Brown had to try several other inanimate substances to convince himself that the motion he observed was not something to do with a life force, but a property of all microscopic matter. This systematic investigation is what won for Brown the accolade of having the jittering motion named after him, work that Ingenhousz didn't need to do.

Today's research into nano-technology now routinely fabricates nano-particles. Controlling them suspended in liquids is quite a task. One method is to use a direct current controlled by a feedback system to cancel out the Brownian motion. The position of the 20 nm polystyrene spheres is monitored by a fluorescence microscope and the voltage across the solution altered accordingly. So far nano-particles have been confined to within 1 micron. Alternatively, the path of the particle can be manipulated by suitable changes of the applied voltage. [Ref: Nature , 10 March 2005 p 156]

Even before the recent advent of nano-technology, Einstein's 1905 paper on Brownian motion is his most cited paper (more than for special relativity or his work on photons). It is used by scientists working on such varied topics as aerosol particles (pollution), the properties of milk, paints, granular media (powders) and semiconductors. [Ref Nature, 20 January 2005 p 216]

Thanks to David Walker for pointing out an error on this page, now corrected. Editor

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