_A._ I have considered, as you bad me, this compounded motion with great admiration. First, it is that which makes the difference between _continuum_ and _contiguum_, which till now I never could distinguish. For bodies that are but contiguous, with any little force are parted; but by this compounded motion (because every point of the body makes an equal line in equal time, and every line crosses all the rest) one part cannot be separated from another, without disturbing the motion of all the other parts at once. And is not that the cause, think you, that some bodies when they are pressed or bent, as soon as the force is removed, return again of themselves to their former figure? _B._ Yes, sure; saving that it is not of themselves that they return, (for we were agreed that nothing can move itself), but it is the motion of the parts which are not pressed, that delivers those that are. And this restitution the learned now call the spring of a body. The Greeks called it _antitypia_. _A._ When I considered this motion in the sun and the earth and planets, I fancied them as so many bodies of the army of the Almighty in an immense field of air, marching swiftly, and commanded (under God) by his glorious officer the sun, or rather forced so to keep their order in every part of every of those bodies, as never to go out from the distance in which he had set them. _B._ But the parts of the air and other fluids keep not their places so. _A._ No: you told me that this motion is not natural in the air, but received from the sun. _B._ True: but since we seek the natural causes of sublunary effects, where shall we begin? _A._ I would fain know what makes the sea to ebb and flow at certain periods, and what causeth such variety in the tides. _B._ Remember that the earth turneth every day upon its own axis from west to east; and all the while it so turneth, every point thereof by its compounded motion makes other circlings, but not on the same centre, which is (you know) a rising in one part of the day, and a falling in the other part. What think you must happen to the sea, which resteth on it, and is a fluid body? _A._ I think it must make the sea rise and fall. And the same happeneth also to the air, from the motion of the sun. _B._ Remember, also, in what manner the sea is situated in respect of the dry land. _A._ Is not there a great sea that reacheth from the straits of Magellan eastward to the Indies, and thence to the same straits again? And is not there a great sea called the Atlantic sea that runneth northward to us? And does not the great south sea run also up into the northern seas? But I think the Indian and the South sea of themselves to be greater than all the rest of the surface of the globe. _B._ How lieth the water in those two seas? _A._ East and west, and rises and falls a little, as it is forced to do by this compounded motion, which is a kind of succussion of the earth, and fills both the Atlantic and Northern seas.