The Story of Alchemy and the Beginnings of Chemistry

[3] See the chapter Molecular Architecture in the Story of the Chemical Elements. Lucretius pictured a solid substance as a vast number of atoms squeezed closely together, a liquid as composed of not so many atoms less tightly packed, and a gas as a comparatively small number of atoms with considerable freedom of motion. Essentially the same picture is presented by the molecular theory of to-day. To meet the objection that atoms are invisible, and therefore cannot exist, Lucretius enumerates many things we cannot see although we know they exist. No one doubts the existence of winds, heat, cold and smells; yet no one has seen the wind, or heat, or cold, or a smell. Clothes become moist when hung near the sea, and dry when spread in the sunshine; but no one has seen the moisture entering or leaving the clothes. A pavement trodden by many feet is worn away; but the minute particles are removed without our eyes being able to see them.