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driven (as into the mouths of rivers) into the two channels of the Atlantic and Southern Ocean, which stretch from north to south, and therefore do not interfere with the order of motion from east to west. The true motion therefore of the waters is most properly taken from these extremities of the world which I have mentioned, where they are not obstructed, but pass through. This is the first experiment. The second is as follows:
Supposing that the tide at the mouth of the Straits of Gibraltar comes in at a certain hour, it is plain that it must come in later at Cape St. Vincent than at the Straits ; later at Cape Finisterre than at Cape St. Vincent; later at Ile de Ré than at Cape Finisterre ; later at Noirmoutier (insulam Hechas) than at Ile de Ré ; later at the mouth of the English Channel than at Noirmoutier; later on the coast of Normandy than at the entrance of the Channel. And so far it is regular; but at Gravelines the order is completely changed (and that with a great leap), the tide coming in at the same time as at the mouth of the Straits of Gibraltar. And this second experiment I refer to the first. For I conceive (as I before said) that in the Indian and Northern Oceans the proper course of the water from east to west is open and perfect; whereas in the channels of the Atlantic and South Sea it is straitened, thwarted, and repelled by the opposition of land, which on both sides stretches along from north to south, and gives no free outlet to the waters, except towards the extremities. But this compulsion of the waters from the Indian Sea to the north, and that from the German Ocean to the south, differ immensely in extent by reason of the different force and quantity if the waters. And hence all the Atlantic Ocean as far as the British Channel yields to the force of the Indian Ocean ; while only the upper part, namely that which lies towards Denmark and Norway, yields to that of the North Sea. Now this must be so. For the two great islands of the Old and New World are by shape and position broad at the north and pointed at the south ; so that the seas towards the south occupy a large space, but the seas towards the north (at the back of Europe, Asia, and America) a small one. Therefore this great mass of waters, which comes from the Indian Ocean and is driven back into the Atlantic, is able to force and push on the course of the waters by a continued succession towards the British Channel, which is a succession towards the north. But that far smaller portion of waters which comes from the North Sea, and has likewise almost a free outlet in its own course towards the west at the back of America, cannot drive the course of the waters towards the south except at the point I have mentioned, about the British Channel. Now it needs must be that between these opposite motions there is some point where they meet in conflict, and where the order of the coming in of the tide is at once changed; as we said happened about Gravelines, which is the point where the currents of the Indian and Northern Sea meet. And that there is a kind of eddy from the contrary tides about Holland has been observed by many, not only from the inversion of the order of the hours of high water (which I have mentioned), but likewise from particular and visible experiment. But if this be so, it returns to this ; that it must needs be that the further the parts and coasts of the Atlantic stretch southward
and approach the Indian Ocean, the earlier does the flow of the tide become in point of precedence, inasmuch as it arises from the proper motion of the Indian Sea; but the further they reach to the north (up to the common point, where they are repelled by the contrary stream of the Northern Sea), the later in subsequence. But that this is so, that experiment of the progression from the Straits of Gibraltar to the British Channel plainly shows. Wherefore I judge likewise that it is high water earlier about the coast of Africa than about the Straits of Gibraltar; and reversing the order, that it is earlier about Norway than about Sweden ; but this I have not ascertained by experiment or history. The third experiment is as follows:
Seas shut in on one side, which are called bays, if they tend in their direction from east to west, which is in correspondence with the proper motion of the waters, have vigorous and strong tides ; but if they tend in a contrary direction, weak and imperceptible
For the Red Sea has a very strong tide ; and the Persian Gulf, which runs more directly to the west, a still stronger. But the Mediterranean, which is the largest bay in the world, with its parts the Gulfs of Lyons and Genoa, the Black Sea, and the Sea of Marmora, and likewise the Baltic, which all turn to the east, have hardly any, or weak ones. But this difference is best displayed in the parts of the Mediter. ranean, which as long as they point to the east or bend to the north (like those I mentioned before) are quiet and without much tide. But when they turn to the west, like the Adriatic, they acquire a notable flow. To which add, that in the Mediterranean what little
ebb there is begins from the ocean, whereas the flow begins from the opposite side, so that the water rather follows its course from the east than the pouring back of the ocean. These three experiments then are all I shall at present use with reference to the second inquiry.
Yet I may add a kind of proof agreeable to the things already spoken, but of an abstruser nature; namely, an argument in favour of this motion from east to west (which I have attributed to the waters) drawn not only from the correspondence of the heavens (whereof I have already spoken) where this motion is in special power and vigour, but likewise from the earth, where it seems forth with to cease ; so that this tendency or motion is truly cosmical, and penetrates everything from the heights of heaven to the depths of the earth. For I understand this rotation from east to west to take place (as it is really found to do) about the north and south poles.
Now the diligence of Gilbert has discovered for us most truly that all earth and every nature (which we call terrestrial) that is not supple but rigid, and as he himself calls it robust, has a direction or verticity, latent indeed and yet revealing itself in many exquisite experiments, towards north and south. Which observation I nevertheless limit and correct, by confining the assertion to the exterior concretions about the surface of the earth, and not extending it to the interior (for that the earth is a magnet was a notion hastily taken up from a very light fancy ; as it is impossible that things in the interior of the earth can be like any substance exposed to the eye of man; for with us all things are relaxed, wrought upon, and softened by the
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sun and heavenly bodies, so that they cannot correspond with things situated in a place where such a power does not penetrate); but the point with which we are now concerned is that the
incrustations or concretions of the earth appear to correspond with the rotations of the heaven, air, and water, as far as consistent and determinate bodies can correspond with liquids and fluids; that is, not that they revolve upon poles, but that they direct and turn themselves towards poles.
For as every revolving orb which turns on fixed poles and has no central motion partakes in a way of both a movable and a fixed nature, so when by the solid or self-determining nature of the body the power of revolving is bound up, the power and desire of self-direction still remains and is increased and united ; so that the direction and verticity towards the poles in rigid bodies is the same thing as revolving upon the poles in fluid.
There remains the third inquiry; whence and in what manner is that six-hourly reciprocation of the tides produced, which coincides with a quarter of the diurnal motion, with the above-mentioned difference ? To understand this, suppose the whole world to be covered with water, as at the deluge. I conceive that the waters, being now in a perfect orb, and no way obstructed, would continually move every day a certain distance from east to west (not a great one indeed, by reason of the wearing out and weakening of this motion in the confines of the earth), since they would be nowhere obstructed or checked by the opposition of land. Suppose, again, the earth to be a single island, stretching out lengthways from north to south, that