be real. The discovery and proof of the graininess of the world seem
especially fascinating for two reasons. First, because of the size of individual
atoms, measurements of atomic properties are usually indirect and
necessarily involve clever manipulations of large-scale measurements to
infer properties of microscopic particles. Second, the historical evolution
of ideas about atomicity shows clearly the real way in which science
progresses. This progression is often nonlinear and involves an interdependence
of physics, chemistry, and mathematics, and the convergence of many
different lines of investigation.
There is also an exalted romance in honoring the great atomists who were
able to pick out organizing principles from the confusing barrage of marketplace
ideas of their time: Democritus and Leucippus, who speculated that the
unchanging substratum of the world was atoms in motion; the debonair
French chemist Lavoisier and his wife (see Fig. 4.1), who established the
conservation of matter in many careful chemical experiments; Dalton, who
perceived the atomicity of nature in the law of multiple proportions of
compounds; Avogadro, who in a most obscure and little-appreciated paper,
postulated that all pure gases at the same temperature and pressure have the
same number of molecules per unit volume; and Maxwell,1 who showed with
his molecular-kinetic theory of gases how macroscopic quantities, such as
pressure and temperature, could be derived from averages over distributions