_A._ His first is, that as in a pyramid of brick, wherein the bricks are so joined that the uppermost lies everywhere over the joint or cement of the two next below it, you may break down a part and leave a cavity, and yet the bricks above will stand firm and sustain one another by their cross posture: so also it is in wheat, hailshot, sand, or water; and so they arch themselves, and thereby the fish is every way secured by an arch of water over it. _B._ That the cause why fishes are not crushed nor hurt in the bottom of the sea by the weight of the water, is the water’s arching itself, is very manifest. For if the uppermost orb of the water should descend by its gravity, it would tend toward the centre of the earth, and place itself all the way in a less and lesser orb, which is impossible. For the places of the same body are always equal. But that wheat, sand, hailshot, or loose stones should make a firm arch, is not credible. _A._ The author therefore, it seems, quits it, and taketh a second hypothesis for the true cause, though the former, he saith, be not useless, but contributes its part to it. _B._ I see, though he depart from his hypothesis, he looks back upon it with some kindness. What is his second hypothesis? _A._ It is, that air and water have an endeavour to motion upward, downward, directly, obliquely, and every way. For air, he saith, will come down his chimney, and in at his door, and up his stairs. _B._ Yes, and mine too; and so would water, if I dwelt under water, rather than admit of vacuum. But what of that? _A._ Why then it would follow, that those several tendencies or endeavours would so abate, impede, and correct one another, as none of them should gravitate. Which being granted, the fish can take no harm; wherein I find one difficulty, which is this: the water having an endeavour to motion every way at once, methinks it should go no way, but lie at rest; which, he saith, was the opinion of Stevinus, and rejecteth it, saying, it would crush the fish into pieces. _B._ I think the water in this case would neither rest nor crush. For the endeavour being, as he saith, intrinsical, and every way, must needs drive the water perpetually outward; that is to say, as to this question, upwards; and seeing the same endeavour in one individual body cannot be more ways at once than one, it will carry it on perpetually without limit, beyond the fixed stars; and so we shall never more have rain. _A._ As ridiculous as it is, it necessarily follows. _B._ What are Dr. Wallis’s suppositions? _A._ He goes upon experiments. And, first, he allegeth this, that water left to itself without disturbance, does naturally settle itself into a horizontal plane. _B._ He does not then, as your author and all other men, take gravity for that quality whereby a body tendeth to the centre of the earth. _A._ Yes, he defines gravity to be a natural propension towards the centre of the earth.