_A._ It is evident; nor can there possibly be any weight, as some suppose there is, of a cylinder of air or water or any other liquid thing, while it remains in its own element, or is sustained and inclosed in a vessel by which one part cannot press the other. ========== CHAPTER II. PROBLEMS OF TIDES. _A._ What makes the flux and reflux of the sea, twice in a natural day? _B._ We must come again to our basin of water; wherein you have seen, whilst it was moved, how the water mounteth up by the sides, and withal goes circling round about. Now if you should fasten to the inside of the basin some bar from the bottom to the top, you would see the water, instead of going on, go back again from that bar ebbing, and the water on the other side of the bar to do the same, but in counter-time; and consequently to be highest where the contrary streams meet together; and then return again, marking out four quarters of the vessel; two by their meeting, which are the high waters; and two by their retiring, which are the low waters. _A._ What bar is that you find in the ocean that stops the current of the water, like that you make in the basin? _B._ You know that the main ocean lies east and west, between India and the coast of America; and again on the other side, between America and India. If therefore the earth have such a motion as I have supposed, it must needs carry the current of the sea east and west: in which course, the bar that stoppeth it, is the south part of America, which leaves no passage for the water but the narrow strait of Magellan. The tide rises therefore upon the coast of America; and the rising of the same in this part of the world, proceedeth from the swelling chiefly of the water there, and partly also from the North Sea; which lieth also east and west, and has a passage out of the South Sea by the strait of Anian, between America and Asia. _A._ Does not the Mediterranean Sea lie also east and west? Why are there not the like tides there? _B._ So there are, proportionable to their lengths and quantity of water. _A._ At Genoa, at Ancona, there are none at all, or not sensible. _B._ At Venice there are, and in the bottom of the straits, and a current all along both the Mediterranean Sea and the Gulf of Venice: and it is the current that makes the tides insensible at the sides; but the check makes them visible at the bottom. _A._ How comes it about that the moon hath such a stroke in the business, as so sensibly to increase the tides at full and change?