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tion here be clearly progressive, viz. the motion of the waters entering at the mouths of the rivers from the sea. st'It may, therefore, happen, in like manner, that an immense collection of waters, rolling from the Indian Ocean, may be compelled and driven into the channel of the Atlantic, and thus overflow both shores at once. It must, therefore, be enquired, whether there is any other channel through which the waters may at the same times be discharged or taken off, and we find there is the South Sea at hand, a sea not less than the Atlantic, but rather wider, and of larger extent, which may suffice for this purpose. \ * And thus at length we come to the Crucial Instance in this subject, and it lies thus. If it be once certainly discovered, that when it is food on the opposite coasts of Florida and Spain, in the Atlantic Ocean, it is also flood on the coast of Peru, and along the coast of China, in the South Sea, then the question is determined by this decisive instance, and the flux and reflux of sea we enquire after, is shewn to happen by a progressive motion, for there is no other sea, or place left, where the return or reflux should be at the same time. And this may most common diously be known, by enquiring of the inhabitants of Panama and Lima, (where the Atlantie

and Southern, oceans are separated by a small isthmus) whether the sea flows on the contrary parts of that isthmus, at the same time, or not.

And this decision, or determination, seems certain, upon a supposition of the stability of the earth; but if the earth revolve, there might thence possibly happen, from the different velocity between the rotatory motion of the earth, and the waters of the sea, a violent protrusion or compulsion of the waters in a heap upwards, so as to make the flux: and á falling of this heap downwards, after it could be kept up no longer, so as to make the reflux. But of this a separate enquiry should be made. Yet


this supposition, it remains equally certain, that the sea must of necessity ebb in some places at the same time that it flows in others.

In like manner, let the nature sought be the latter of these two motions; viz. the motion of the sea spontaneously rising up, and subsiding again. If it should happen, that upon a careful examination, the progressive motion we speak of must be rejected, then the cross-way of this nature would lie thus, or go off in three different roads. For it must necessarily happen, that this motion, whereby the waters rise in flowing, and again fall back in ebbing, (without any additional waters joining them) must proceed in one of these three ways, viz. 1. either this quantity of

rs, remain

ed but waters must spring, or fow, from the bowels of the earth, and again fall back into its' receptacle; or, 2. the quantity of water is not enlarged, but only the same quantity extended, or Tarified, so as to possess a greater space, or dimension, and again contracted ; or, 3. neither the quantity nor the bulk is enlarged, but the waters, ing both of the same weight and density, are rais

some attractive virtue, that draws them upwards, and calls them forth by consent, and then permits them to go again.

Therefore, dropping the two other motions, let the enquiry, for example, be reduced to the last; and the question will be, whether any such rising may happen by a consent, or attractive virtue. And here, in the first place, it is manifest, that all the waters, as they lie collected in the cavity, or bason of the sea, cannot be lifted

up mass together, for want of something to succeed them at the bottom; and therefore, though they had any such appetite of raising themselves, yet it would be broken and prevented by the connection of things; or, as the common phrase is, by 'nature's abhorrence, or dread of leaving a vacuum behind. - It remains, therefore, that they must rise in one part, and consequently be dimi


in one

* Nothing, by supposition, could here succeed but atmospherical air.

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shor? nished and give way in another; whence again it will follow, that the attractive virtue, as it can not operate equally upon the whole, must operate strongly upon the middle, so as to raise thę waters there; and when they are thus raised, the the waters *

Thus, at length, we come to the Crucial In. stance. For if it be found, that in the ebbing of the

seą the surface of the water is more arched, and spherical, while the waters rise up in the middle, and leave the sides, that is, the shores, shallow. ;

and if in the flowing, the same surface become more flat and equal, viz. whilst the waters return to their former situation, then it may doubtless be admitted that the sea rises by attraction, or otherwise it should be totally rejected. And it were not difficult to try, by the sounding line in streights, whether in the tide of ebb towards the middle of the sea, the sea be not deeper and higher than in the tide of flood. But if this shall prove the case, it must be observed, that, contrary to the common opinion, the wa: ters rise in the ebb, and fall in the flood, so as


*As is now generally allowed to be the case. See Sir Isaac Newton's Theory of the Tides, explained by Dr. Halley in the philosophical Transactions, No. 226. 1 t 12 ,

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in the letter only to cover and overflow the shores. "

Again, let the nature sought be the spontaneous motion of rotation ; and in particular, whether the diurnal motion, whereby the sun and stars rise and set, to the sight, bé a true motion of rotation in the heavenly bodies, or only apparent in them, and real in the earth. The following may be a Crucial Instance in this enquiry. If any motion, from east to west, is found in the ocean, though it be ever so languid and feeble, if the same motion be found somewhat quicker in the air, especially between the tropics, where, because of the larger circles, it will be more per-' ceptible, if the same motion be found brisk and strong in the lower comets, if the same motion be found in the planets, so dispensed and proportioned, that the nearer it comes to the earth, the slower it proves, and the farther off the quicker, but quickest of all in the sphere of the fixed stars, then doubtless the diurnal motion should be received for real in the heavens, and the motion of the earth be rejected, because it would then be manifest that the motion from east to west is perfectly cosmical*, and by consent of the universe, which having the greatest

Viz. As belonging to the whole system of things.

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