(chemistry) any theory in which all matter is composed of tiny discrete finite indivisible indestructible particles. Synonyms:atomism, atomist theory, atomistic theory.
... very attenuated it becomes fire, when more condensed, wind, and then cloud; and when still more condensed, water and earth and stone; and all other things are composed of these; and he regards motion as eternal, and by this changes are produced." We have here a distinct adumbration of the atomic theory in its most defensible form— that is to say, a conception which makes the differences in various substances consist in differences in condensation or rarefaction of the particles of the primary substance. The simple normal ... — Nature Mysticism • J. Edward Mercer
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