Full Idea
Democritus said that the properties of the atoms are in number two, magnitude and shape, but Epicurus added to these a third one, weight.
Gist of Idea
Democritus says atoms have size and shape, and Epicurus added weight
Source
report of Epicurus (fragments/reports [c.289 BCE]) by Pseudo-Plutarch - On the Doctrine of the Philosophers 1.3.18
Book Reference
Democritus: 'Early Greek Phil VII: Democritus', ed/tr. Laks,A/Most,G [Harvard Loeb 2016], p.109
A Reaction
The addition of Epicurus seems very sensible, and an odd omission by Democritus. He seems to think that atoms have a uniform density, so that volume indicates weight.
Related Ideas
Idea 20903 The only distinctions are Configuration (shape), Disposition (order) and Turning (position) [Democritus, by Aristotle]
Idea 20919 How can things without weight compose weight? [Alexander]