II
Democritus avers that when there are many particles, which he calls atoms, in a small empty space (i.e. vacuum), wind is the outcome. But, on the contrary, when the space is large and the particles few, there is a still peaceful condition of the atmosphere. To illustrate: in the market square or in a side street as long as there is a sprinkling of people there is no disturbance as one walks along it; but when a crowd meets in a narrow space, then they jostle against each other, and quarrelling arises. Similarly in this space which surrounds our earth; when many bodies have crowded a very small portion, it is unavoidable that they should jostle one another and be driven back and forward, and be intertwined and squeezed. Hence results wind; the particles that were struggling have had to give way, and after being tossed about and remaining in suspense for a long time they at length lean their weight toward one side. But when a few bodies occupy a large roomy place, they can neither ram each other nor be jostled by one another.