having in this Book inferted a Table of fixed Stars, their Declinations, &c. I fhall refer the Reader to it, the Sun and Stars being fufficient in all Cafes for taking Obfervations.

Of the General Motion of the Tides, and how to know the Time of High-Water at any known Port, only by a Sight of the Moon at any Time of the Day or Night.

THEY that would be able to give a good Account of the Tides, or of the Time of High-Water or LowWater, at any Port or Harbour propofed, it is neceffary, in order thereunto, that there be a right Understanding of the original Caufe of the Motion of the Tides, or Ebbing and Flowing of the Sea; a Thing which hath been often in Difpute among the Learned, both Mathematicians and Philofophers, whofe different Sentiments have rendered the Thing as dubious as when they first began with it; fome afcribing the Fluctuation of the Sea to the fwift Motion of the Earth, according to the Cupernican System, and that the Water being a fluid Body, and not presently acquiring fo fwift an Agitation as the Earth itself, it must confequently be higher Water upon one Part of the Globe than upon another, and this they illuftrate thus: Suppose a Boat under Sail, with fresh Way, and a fmall Quantity of Water in the Boat, it feems very plain, that the fwift Motion of the Boat would make the Water incline rather towards the Stern of the Boat; but if the Boat, when failing with that Speed, fhould by coming afhore, or fome other Accident, meet with a fudden Interruption, and at once ftand ftill, the Water fill retaining in fome Measure its former

Motion will presently run to the fore Part of the Boat, and by this they would fome Way or other demonftrate, that the Motion of the Tides depends upon the Motion of the Earth: But to use no other Arguments for the Confutation of this Opinion, the Abfurdity hereof will appear in this; that if the Motion of the Earth were the original Cause of the Motion of the Tide, then the Tide muft neceffarily follow the Motion of the Earth, (or to our Appearance the Motion of the Sun) and confequently it must always be High-Water at one Place, at one and the fame Time of the Day; but the contrary is fo evident to all, that there needs no more be faid to disprove it.

Others fay, the Flowing of the Tide is occafioned by a great Confluence of Water proceeding from the Mael-ftream, (called by fome the Navel of the Sea, being (as it is reported) an Eddy or Whirl-pool, under the Weft Coaft of Norway, or Finmark, from whence (it is faid during the fix Hours Flood, the Water iffues violently out, and occafions the Rifing or Flowing of the Water in all the adjacent Parts, and finks with the fame Violence during the Ebb; fo that it is faid, that during the Flood, the heaviest Metal will not fink; and during the Ebb, the lightest Subftance, or the best of Ships will not fwim; but what Reason they will give why this Ebbing and Flowing fhould be regulated and governed by the Motion of Moon, I do not underftand, unless this Iffue of Water be fupplied by fome Communication that it hath with the Eastern Seas, by fome Paffage under the Main Continent of Norway, but this being an Uncertainty, we fhall wave it, as well as the Opinion of a third Sort, who affirm that God, who created all Things, gave Life to all his Creatures; and that the Ebbing and Flowing of the Sea is no more but the Breathing of the Earth, which feems to me a very odd Fancy, and not worth inferting, had it not been in this Collection of the various Opinions of the Learned upon this Subject. I fhall among the reft, deliver my own Opinion in the Matter; and although I do not think myself able infalliably to give a definitive Sentence in the Cafe, yet I fhall endeavour to prove it

to

to be confiftent with the Obfervation and Experience of our Mariners, and fhall answer what Objections can easily be made against it.

It is evident to all that own the Retundity of the Earth, (a Thing generally out of Controversy amongst the Learned) that there is a Principle of Graviation towards the Center of the Earth, and that this attractive Influence is diffused to all Beings whatsoever within the Orb thereof; and hence it is, that we that inhabit the Earth find no fuch Thing as an upper Side and an under Side of the Earth, but in all Parts of the Superficies thereof we find a like natural Tendency towards its Centre, as it is evident by the Experience of those that have failed about the World, and yet in their fo far different (if not diametrically oppofite) Places that they have failed to, have found themfelves and every particular Thing to have the fame preffing Inclination towards the Center of the Earth, which feemed to them to be downwards, as well as it doth to us. Now if we grant the Earth this ftrong Principle of Gravitation, Inclination, or Attraction towards its Center, which Reason and common Experience proves, we have Reafon from thence to believe, that the other Bodies, as the Sun and Moon, have the fame Principles of Gravitation towards their Centers, (which may be proved by fome Reasons, which, to infert here, would be too great a Digreffion from the prefent Subject) which being granted, I fuppofe the Ebbing and Flowing of the Sea to be occafioned by the Attraction of the Sun and Moon (especially the Moon being a fecondary Planet, which moves far nearer the Earth, and refpect it for her Center) the Strength of which Attraction, although it cannot have any Influence upon the folid Part of the Earth, yet the Water being a fluid Subftance, is more easily affected with this attracting Power, and by Virtue thereof, (while the Earth continues round) the Water is gently fucked and drawn into an oval Form, by Reafon of its inclining Tendency towards those attractive Bodies, thereby caufing High-Water where the Ends of the Oval is, and confequently Low-Water at the Middle of the Oval, as may be demonstrated

N 3

thus;