The ultimate and indivisible constituents of matter are extremely small and imperceptible particles called atoms. These, like matter itself, are eternal and indestructible. The differences between substancess are due to the elements of which they are formed, which may differ from each other in the size, shape and arrangements of the atoms of which they are composed. The properties of a substance which we observe are not the properties of its atoms but properties which arise from the manner in which the atoms are combined. Second, these atoms are constantly in motion and this motion is a property inherent in them, as motes of dust are seen to dance in a sunbeam.
Combinations are due to coalescence of the particles or atoms as they collide.
Third, these atoms are separated from each other by void, or vacuum, in which the atoms move. It is tempting to read more into the atomistic philosophers in the light of our modern knowledge of atoms than they actually did write. Like other Greek thought, theirs was based upon logic and argument rather than experiment. Nevertheless, the idea of atoms originating with them had, by 1750, been spread through the scientific community and was the foundation stone for the work of John Dalton. The other pure substances known in the ancient world, in addition to naturally-occurring minerals, constitute rather a mixed group.