Thus then the earth’s ponderous mass was formed With close-packed body, and all the slime of the world Slid to the lowest plane by its own weight, And at the bottom settled down like dregs. Then the sea, then the air, then the fire-laden Aether itself, all these were now left pure With liquid bodies. Some indeed are lighter Than others, and most liquid and light of all Over the airy currents aether floats, Not blending with the turbulent atmosphere Its liquid substance. All below, it suffers To be embroiled by violent hurricanes, Suffers all to be tossed with wayward storms, While itself gliding on with changeless sweep Bears its own fires along. For, that the aether May stream on steadily with one impulse, The Pontos demonstrates, that sea which streams With an unchanging tide, unceasingly Preserving as it glides one constant pace. Now let us sing what cause could set the stars In motion. First, if the great globe of heaven Revolves, then we must needs maintain that air Presses upon the axis at each end, And holds it from outside, closing it in At both poles; also that there streams above Another current, moving the same way, In which the stars of the eternal world Roll glittering onward; or else that beneath There is another stream, that drives the sphere Upwards the opposite way, just as we see Rivers turn mill-wheels with their water-scoops. It likewise may well be that the whole sky Remains at rest, yet that the shining signs Are carried onwards; either because within them Are shut swift tides of aether, that whirl round Seeking a way out, and so roll their fires On all sides through the sky’s nocturnal mansions; Or else that from some other source outside An air-stream whirls and drives the fires along; Or else they may be gliding of themselves, Moving whithersoever the food of each Calls and invites them, nourishing everywhere Their flaming bodies throughout the whole sky. For it is hard to affirm with certainty Which of these causes operates in this world: But what throughout the universe both can And does take place in various worlds, created On various plans, this I teach, and proceed To expound what divers causes may exist Through the universe for the motion of the stars: And one of these in our world too must be The cause which to the heavenly signs imparts Their motive vigour: but dogmatically To assert which this may be, is in no wise The function of those advancing step by step.