_B._ All this would not make a visible difference between high and low water, because this motion being so regular, the unevenness would not be great enough to be seen. For though in a basin the water would be thrown into the air, yet the earth cannot throw the sea into the air. _A._ Yes; the basin, if gently moved, will make the water so move, that you shall hardly see it rise. _B._ It may be so. But you should never see it rise as it doth, if it were not checked. For at the straits of Magellan, the great South sea is checked by the shore of the continent of Peru and Chili, and forced to rise to a great height, and made to run up into the northern seas on that side by the coast of China; and at the return is checked again and forced through the Atlantic into the British and German seas. And this is done every day. For we have supposed that the earth’s motion in the ecliptic caused by the sun is annual; and that its motion in the equinoctial is diurnal. It followeth therefore from this compounded motion of the earth, the sea must ebb and flow twice in the space of twenty-four hours, or thereabout. _A._ Has the moon nothing to do in this business? _B._ Yes. For she hath also the like motion. And is, though less swift, yet much nearer to the earth. And therefore when the sun and moon are in conjunction or opposition, the earth, as from two agents at once, must needs have a greater succussion. And if it chance at the same time the moon also be in the ecliptic, it will be yet greater, because the moon then worketh on the earth less obliquely. _A._ But when the full or new moon happen to be then when the earth is in the equinoctial points, the tides are greater than ordinary. Why is that? _B._ Because then the force by which they move the sea, is at that time, to the force by which they move the same at other times, as the equinoctial circle to one of its parallels, which is a lesser circle. _A._ It is evident. And it is pleasant to see the concord of so many and various motions, when they proceed from one and the same hypothesis. But what say you to the stupendous tides which happen on the coasts of Lincolnshire on the east, and in the river of Severn on the west? _B._ The cause of that, is their proper situation. For the current of the ocean through the Atlantic sea, and the current of the south sea through the northern seas, meeting together, rise the water in the Irish and British seas a great deal higher than ordinary. Therefore the mouth of the Severn being directly opposite to the current from the Atlantic sea, and those sands on the coast of Lincolnshire directly opposite to the current of the German sea, those tides must needs fall furiously into them, by this succussion of the water. _A._ Does, when the tide runs up into a river, the water all rise together, and fall together when it goes out?