Note (return) — Chapter XIII
Reading edition
"The atoms are in a continual state of motion" and "have moved with equal rapidity from all eternity, since it is evident the vacuum can offer no resistance to the heaviest, any more than the lightest." The primary and original movement of all atoms is in straight lines, by virtue of their own weight. The vacuum separates all atoms one from another, at greater or less distances, and they preserve their own peculiar motion in the densest substances. 797