"Almost all philosophers, ancient and modern, fearing an eternal confusion of the elements, were they all endowed with weight, conceived the two uppermost to be furnished with a certain levity, by means of which they bounded up on high, each to occupy its peculiar place, like as the two lower ones are pushed downwards by their own weight. But having clearly shewn in the last Essay, that levity is not necessary for that effect, weight alone being sufficient, I embrace the maxim, which they themselves have prudently laid down, that we should never multiply existences unnecessarily; assuming that God and Nature do nothing in vain, (which they also teach.) I think it would be otherwise were we to admit levity, since it is of no use."