Brown's 'Brownian motion' revisited.
Daniel H. Deutsch of Pasadena, Calif., sparked the controversy last year when he contended that the vigorous motion Brown had observed through his microscope resulted largely from causes other than bombarding molecules. In particular, Deutsch emphasized that because Brown's samples remained uncovered during observation, effects such as evaporation and vibration could induce the movements he saw (SN: 5/4/91, p.287).
This salvo caught the attention of Brian J. Ford of Eastrea, England, an expert microscopist who has actually worked with several of the microscopes that Brown himself used. "These microscopes are all beautifully made brass instruments," Ford says. "They're about 5 or 6 inches tall. They screw into the lid of the mahogany box ... in which the components are housed. Their high-power lenses are well capable of [resolving] a living bacterium -- but only if you use them properly."
Last month at INTER/MICRO-92, held in Chicago, Ford presented a 25-minute videotape showing the erratic movements of tiny carbon particles in diluted India ink, microscopic oil droplets in milk, and minuscule particles inside a pollen grain -- as viewed through one of Brown's microscopes. "It [presents] an instantly recognizable and highly detailed portrayal of Brownian movement," Ford says. "If you just showed it at a student lecture and said, 'This is what Brownian movement looks like through a modern microscope,' nobody would even stop to question the fact."
Ford took particular care to duplicate Brown's observations of pollen grains from a plant known as Clarkia pulchella. Each grain, about 50 or 60 microns wide, contains a thick liquid held in place by translucent walls. When Brown looked inside the pollen grains with his microscope, he could see tiny particles, each about 1 micron across, suspended in the liquid and constantly in motion.
Deutsch readily concedes that both Brown and Ford were seeing some kind of movement. But he insists that neither saw true Brownian motion. In a letter in the June 4 NATURE, Deutsch states: "I doubt the interpretation, not the observation. Particle motion in Brown's methodology is too vigorous by orders of magnitude to be proper Brownian motion."
Deutsch argues that for Brown's pollen grains, the presence of water alone causes a variety of effects, including rupture of the grains, that Brown didn't take into account. "There's a whole series of physical and chemical processes that take place," he says. "It all happens rather rapidly, and unless you're aware of these things ... you miss them."
He adds, "If you were to compare what you see under Brown's microscope using his conditions and take the same solution and put it under a modern microscope, using modern techniques, then you would see something quite different."
"Deutsch is acting as if people from an earlier era were too dumb to know what they were doing, but Brown was a most precise investigator," Ford replies. Indeed, according to Ford, Brown carefully checked into and discredited just the kinds of confounding effects that Deutsch mentions.
Last year, Ford offered Deutsch a wager. "If he were willing to take the bet, I gladly offered to eat my hat if I couldn't [succeed in getting the images]," Ford says. "I did write to him to say that I had now done it and that I hoped they make hat-shaped gateaux in Pasadena."
But Deutsch isn't ready to concede yet. He's hard at work preparing a paper to present his own views in more details.
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|Title Annotation:||botanist Robert Brown's motion theories made in 1827 being questioned|
|Date:||Aug 15, 1992|
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