_B._ No, unless I could make one and the same thing heavier than it was. God hath from the beginning made all the kinds of hard, and heavy, and diaphanous bodies that are, and of such figure and magnitude as he thought fit; but how small soever, they may by accretion become greater in the mine, or perhaps by generation, though we know not how. But that gold, by the art of man, should be made of not gold, I cannot understand; nor can they that pretend to show how. For the heaviest of all bodies, by what mixture soever of other bodies, will be made lighter, and not to be received for gold. _A._ Why, when the cause of gravity consisteth in motion, should you despair of finding it? _B._ It is certain that when any two bodies meet, as the earth and any heavy body will, the motion that brings them to or towards one another, must be upon two contrary ways; and so also it is when two bodies press each other in order to make them hard; so that one contrariety of motion might cause both hard and heavy, but it doth not, for the hardest bodies are not always the heaviest; therefore I find no access that way to compare the causes of different endeavours of heavy bodies to descend. _A._ But show me at least how any heavy body that is once above in the air, can descend to the earth, when there is no visible movent to thrust or pull it down. _B._ It is already granted, that the earth hath this compounded motion supposed by Copernicus, and that thereby it casteth the contiguous air from itself every way round about. Which air so cast off, must continually, by its nature, range itself in a spherical orb. Suppose a stone, for instance, were taken up from the ground, and held up in the air by a man’s hand, what shall come into the place it filled when it lay upon the earth? _A._ So much air as is equal to the stone in magnitude, must descend and place itself in an orb upon the earth. But then I see that to avoid vacuum, another orb of air of the same magnitude must descend, and place itself in that, and so perpetually to the man’s hand; and then so much air as would fill the place must descend in the same manner, and bring the stone down with it. For the stone having no endeavour upward, the least motion of the air, the hand being removed, will thrust it downward. _B._ It is just so. And farther, the motion of the stone downward shall continually be accelerated according to the odd numbers from unity; as you know hath been demonstrated by Galileo. But we are nothing the nearer, by this, to the knowledge of why one body should have a greater endeavour downward than another. You see the cause of gravity is this compounded motion with exclusion of vacuum.