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. III The falsity of this view may be inferred merely from the fact that 1 wind by no means invariably accompanies a cloud-laden atmosphere, and yet more particles have gathered at that than at any other time in a narrow space, where they produce condensation and heaviness in the clouds. Besides, in the neighbourhood of rivers and lakes cloud is frequent from the confinement and accumulation of particles, and yet there is no attendant wind. Indeed, sometimes such a darkness over-spreads the place that the view of objects in the immediate vicinity is cut off; which would never happen unless numerous particles were massed in a small space. Yet no period is more free from 2 wind than a period of cloud. Add now a consideration of an opposite character: When the sun rarefies at his rising the thick dank morning air, then a breeze springs up; the particles have got more room now, and the thickly packed crowd of them is broken up. IV