Democritus (460-370 BCE)
A Greek philosopher who developed a theory (atomism) that suggested that all
phenomena are to be explained by the incessant movement of atoms, differing only
in shape, order, and position.
He believed that the hard atoms of the four primitive elements (earth, air,
water, and fire) moved in a vacuum. The shape and size of these atoms explained
some of their properties. For example, the atoms of fire were tiny spheres
which, because of their smooth surfaces, did not link with the atoms of the
other elements. The atoms of earth, air, and water had shapes which enabled them
to connect with each other and form visible matter.
Source: Metcalfe, H. Clark, John E. Williams, and Joseph F. Castka 1974.
Modern Chemistry. New York, NY. Holt, Rinehart and Winston