Existence of atoms reaffirmed

By Aussiegirl

According to the Wikipedia article on atomic theory, In the late 19th century, a movement led by Ernst Mach, Wilhelm Ostwald, and Karl Pearson rejected the atomic theory on epistemological grounds. The dispute was not finally settled until Jean Perrin's experimental investigation of Einstein's mathematical theory of Brownian motion in the early 20th century. This interesting article describes the experiment that reaffirmed the existence of atoms. Notice that, even though John Dalton had already developed his theory based on experiment, somehow Mach, Ostwald, and Pearson, although good scientists themselves, decided that experiment should be ignored in favor of an epistemological, i.e. non-experimental, approach. Even Homer nods.
I also learned from the Wikipedia article that atomic theory was first developed in the 6th century B.C. in ancient India by Hindu, Buddhist, and Jaina philosophers, predating the Greeks by a whole century. And they had an even more sophisticated theory -- to quote Wikipedia again: They developed detailed theories of how atoms could combine, react, vibrate, move, and perform other actions, and had particularly elaborate theories of how atoms combine, which explains how atoms first combine in pairs, and then group into trios of pairs, which are the smallest visible units of matter. This parallels with the structure of modern atomic theory, in which pairs or triplets of supposedly fundamental quarks combine to create most typical forms of matter. They had also suggested the possibility of splitting an atom.
For completeness, here is the Wikipedia article on Brownian motion.

PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 779 June 2, 2006 by Phillip F. Schewe, Ben Stein, and Davide Castelvecchi

EXISTENCE OF ATOMS REAFFIRMED. A new experiment has reproduced a landmark 1908 study demonstrating the physical existence of atoms, even to many of those (such as the chemist William Ostwald) who had doubted that matter consisted of microscopic particles rather than being continuous in nature. The new experiment, conducted partly as an educational exercise for undergraduates at Harvard, reproduced (with modern equipment) the work in 1908 of Jean-Baptiste Perrin, a French physicist, who in turn was seeking to test a prediction of Albert Einstein. Einstein's miraculous 1905 output included famous papers on special relativity (bearing on features of space-time and on the equivalence of matter and energy) and the photoelectric effect (explaining the quantum nature of light). The propositions of relativity and
quantum theory proved to be extremely fruitful and are put to frequent experimental test. A third paper from that year, one devoted to explaining Brownian motion, is perhaps less well known, but also of great importance. Brownian motion, first observed by Robert Brown in 1827, is the jostling of one set of tiny particles (in this case pollen grains) by other, even smaller, particles (the surrounding water molecules). Einstein interpreted the jostling as the incessant and fluctuating aggregate effect of all the presumed atoms or molecules on the grains; occasionally the net force on the grain would push it to the side. Einstein worked out a formula relating the size of the pollen grains and their median momentary excursion (part of what we would now call a "random walk") and the size of the surrounding and invisible buffeting particles (atoms and molecules). Perrin performed his experiment using emulsions containing microscopic particles of gamboge (a type of pigment) or mastic (a clear plastic). Using a microscope he painstakingly watched, measured, and tabulated many displacements of individual gamboge particles. From this he confirmed Einstein's predictions about the statistical nature of the agitations, and from this one could calculate Avogadro's Number, the number of atoms or molecules in a single mole of that substance. And this in turn supported the atomistic view of matter. The new Harvard version of this experiment is faithful to the 1908 work except that a CCD camera viewed the particle movements and analyzed the displacements by means of a computer program. (Newburgh, Peidle, and Rueckner, American Journal of Physics, June 2006)