_B._ Yes; for the endeavour of the quicksilver both from A and D downward, is stronger than that of the oil downward. If, therefore, the endeavour of the quicksilver were not resisted by the bottom B C, it would fall so, by reason of the acceleration of heavy bodies in their descending, as to leave the oil, so that it should not only not press, but also not touch the quicksilver. It is true, in a pair of scales equally charged with quicksilver, that the addition of a little oil to either scale will make it preponderate. And that was it deceived him. _A._ It is evident. The last experiment he cites is the weighing of air in a pair of scales, where it is found manifestly that it has some little weight. For if you weigh a bladder, and put the weight into one scale, and then blow the bladder full of air, and put it into the other scale, the full bladder will outweigh the empty. Must not then the air gravitate? _B._ It does not follow. I have seen the experiment just as you describe it, but it can never be thence demonstrated that air has any weight. For as much air as is pressed downward by the weight of the blown bladder, so much will rise from below, and lay itself spherically at the altitude of the centre of gravity of the bladder so blown. So that all the air within the bladder above that centre is carried thither imprisoned, and by violence: and the force that carries it up is equal to that which presseth it down. There must, therefore, be allowed some little counterpoise in the other scale to balance it. Therefore, the experiment proves nothing to his purpose. And whereas they say there be small heavy bodies in the air, which make it gravitate, do they think the force which brought them thither cannot hold them there? _A._ I leave this question of the fish as clearly resolved, because the water tending every way to one point, which is the centre of the earth, must of necessity arch itself. And now tell me your own opinion concerning the cause of gravity, and why all bodies descend or ascend not all alike. For there can be no more matter in one place than another if the places be equal. _B._ I have already showed you in general, that the difference of motion in the parts of several bodies makes the difference of their natures. And all the difference of motions consisteth either in swiftness, or in the way, or in the duration. But to tell you in special why gold is heaviest, and then quicksilver, and then, perhaps, lead, is more than I hope to know, or mean to enquire; for I doubt not but that the species of heavy, hard, opaque, and diaphanous, were all made so at their creation, and at the same time separated from different species. So that I cannot guess at any particular motions that should constitute their natures, farther than I am guided by the experiments made by fire or mixture. _A._ You hope not then to make gold by art?