about new and full moon, being then about 24h. 37m. about thetime of the moon’s quadratures it is 2oh. 27m. These valuesare taken from a mean of many observations made at Barbadoes by Dr. M iskelyiie. 7. The tides in similar circumstances aregreatest when the moon is at her smallest distance from the earth,or in her perigee, and, gradually diminishing, are smallest whenshe is in her apogee. 8. The same remark is made with respectto the sun’s distance, and the greatest tides are observed duringthe winter months of Europe . 9. The tides in any part of theocean increase as the moon, by changing her declination, ap-proaches the zenith of that place. 10. The tides which happenwhile the moon is above the horizon are greater than the tides of.the same day when the moon is below the horizon.” There isalso a kind of rest or cessation of about half an hour between theflux and reflux : during which time the water is at its greatestheight, called high water. The flux is made by the motion of thewater of the sea from the equator towards the poles : w hich, in itsprogress, striking against the coasts in its way, and meeting withopposition from then), swells, and where it can find passage, as inflats, rivers, &c. rises up and runs into the land. This motion fol-lows, in some measure, the course of the moon ; as it loses or comeslater every day’ by about three quarters of an hour, or, more pre-cisely, by 48 minutes, and by so much is the motion of the moonslower than that of the sun. ft is always highest and greatest infull moons, particularly those of the equinoxes. In some parts, asat mount St. Michael, it rises 80 or 90 feet, though in the open seait never rises above a foot or two ; and in some places, as about theMorea, there is no flux at all. It runs up some rivers above120 miles. Up the river Thames it only goes 80, viz. near toKingston in Surry. Above London bridge the water flows fourhours and ebbs eight; and below the bridge, flows five hours andebbs seven. Horner is the earliest profane author who speaks ofthe tides. But (in the Xllth book of Odyssey) he only takesnotice of the tides of Charybdis, which rise and retire thrice inevery day. Herodotus and Diodorus Siculus speak more dis-tinc.ly of the tides in the Bed Sea. I’ytiieas of Marseilles is thefirst who says any thing of their cause. According to Strabo hehad been in Britain , where he must have observed the tides of theocean. Plutarch says expressly that l’ytheas ascribed them to themoon. It is surprising that Aristotle says so little about the tides.The army of Alexander, his pupil, were startled at their first ap-pearance to them near the Persian Gulph ; and we should havethought that Aristotle would be w ell informed of all that had beenobserved there. But there are only three passages concerning themin all Aristotle ’s writings, and they are very trivial. In one placehe speaks of great tides observed in the north of Europe ; in ano-ther, he mentions their having been ascribed by some to the moon ;and in a third, he says, that the tide in a great sea exceeds that in asmall one. The conquest and the commerce of the Romans givethem more acquaintance with tides; Catsar speaks of them in the4th book of his Gallic War. Strabo, after Posidonius , classes thephenomena into daily, monthly, and annual. lie observes, thatthe sea rises as the moon gets near the meridian, whether above orbelow the horizon, and falls again as she rises or falls : also, that the(ides increa-e at the lime of new and full moon, and the greatest atthe summer-solstice. Pliny explains the phauiomcna at somelength ; and says, that botii the sun and moon arc their cause, drag-ging the wave along with them (B. II. c. 97.) Senccal, (Nat.Quest. III. 23,) -peaks of the tides with correctness ; an d M aero-bins (Sonin. Scip. I, (i,) gives a very accurate description of theirmotions. Such plixnony tia however could not hut exercise humancuriosity as to their cause. Plutarch , (Plant. Phil. III. 17,) Gali-leo (Syst. Mund. Did. 4,) lLccioli hi the Almagest, ii. p. 374,and Gassendi , ii. p. 27. have collec ted most ol the notions of theirpredecessors on the subject ; but they are of so little importance,that they do not deserve notice. Kepler speaks more like aphilosopher (De Stella Mavtis, and Enit. Astrnn. p 5i5.) He saysthat all bodies attrac t each other, and that the w aters of the ocean Iwould all eo ta the nnmii were they not retained by the attractionof the earth ; Slid tlu-n goes -m to explain their elevation underthe moon a-d on the opposite side, because the earth is less at-tracted by die moon than die nearer waters, but more than tinwaters which art more remote. The honour of a complete expiaiuition of the tides was reserved to Sir Isaac New ton. He hudhold of this class of phenomena as the most incontestable proof oi

universal gravitation, and has given a most beautiful and synopticalview of the whole subject ; contenting himself, however, withmerely exhibiting the chief consequences of the general principle,and applying it to the phenomena with singular address. But thewide steps taken by this great philosopher in his investigation leaveordinary readers frequently at fault: many of his assumptionsrequire the greatest mathematical knowledge to satisfy us of theirtruth. The academy of Paris therefore proposed to illustrate thisamong other parts of the principles of natural philosophy, andpublished the theory of the tides as a piize problem. This pro-duced three excellent dissertations by MT.aurin. Dan. Ber-noulli, and Euler . We have demonstrated in our dissertationson the physical principles of the celestial motions, that it is anunexpected fact, that every particle of matter in the solarsystem is actually deflected toward every other particle; andthat the deflection of a particle of matter towards any distant sphereis proportional to the quantity of matter in that sphere directly,and to the square of the distance of the particle from the centreof that sphere inversely ; and having found that the heaviness ofa piece of terrestrial matter is nothing but the supposed oppo-nent to the force which we exert in carrying this piece of matter,we conceive it as possessing a property or distinguishing quality,manifested by its bi i ig gruvis, or h xivy. This is heaviness, orgravity; and the manifestation of this quality, or the event inwhich it is seen, whether it be directly falling, or deflecting in aparabolic curve, or stretching a coiled spring, or breaking a rope,or simply pressing on its support, is gravitatio, gravitation ; and thebody is said to gravitate. When all obstacles are removed fromthe body, as when we cut the string by which a stone is hung, itmoves directly downwards, tendit ad terrain. By some metaphysicalprocess, this liisus ad motum has been called a tendency in ourlanguage, and is used to signify the energy of any active qualityin those cases where its simplest and most immediate manifestationis prevented by some obstacle. The stretching the string in adirection perpendicular to the horizon is a foil manifestation of thistendency. This tendency, this energy of its heaviness, is thereforenamed by the word which distinguishes the quality called gravi-tation. But Sir Isaac Newton discovered that this deflection of aheavy body differs in no respect from that general deflectionobserved in all the bodieumf the solar system, for 16 feel, whichis the deflection of a stone in one second, has the very same pro-portion to T \y of an inch, which is the simultaneous deflection of themoon, that the square of the moon’s distance from the centre of theearth has to the square of the stone’s distance from it, namely,that of 360d to 1. Thus we are enabled to compare all the effectsof the mutual tendencies of the heavenly bodies with the tendencyof gravity, whose effects and measures are familiar to u : . If theearth were a sphere covered to a great depth with water, the waterwould form a concentric spherical shell ; for the gravitation ofevery particle of its surface would then be directed to the centre,and would he equal. The curvature of its surface therefore wouldhe every where the same, that is, it would be the uniform curva-ture of a sphere. See Geography, and Astronomy. Thetidesarc scarcely sensible in the Mediterranean Sea . However, tidesarc observed there, and still more remarkable in the Adriatic. Wedo not know that tides have been observed in the great lakes ofNorth America . These (ides, though small, should be very regu-lar. It would he low water on one .side of the shore when itis high water on the other side of this partition. If the tides in theEuxine and Caspian Seas , or in (he American lakes which arcnear each oilier, could be observed, this phenomenon should ap-pear, and would be one of the prettiest examples of universalgiavit..tion that can he conceived. Something like it is to be seenill G'hrahar. It is Imili water on the E. side ot the rock about 1°o'clock at full and change, and it is high water on the W. side, nota mile UlsiaiU, at 12. This difference is perhaps the chief causeut the singular current which is observed in the mouth of theStraits. 1 i.ere are three curren’s ob-ervid at the same time,w liicli change their directions every 12 Hours. The small tide ofthe Yieditrir.inean proceeds along the Barbary shore, which ' swry tmifoim dl the wav from E.iypt, with tolerable regularity*But along ill'.- N. side, where .1 is greatly obstructed by Italy , theislands, and the E Coast ot Spun, it sits vert irregular', ; andtin* perceptible high water on t e Spanish coast, differs four hoursfrom that on the S. coast. Thus one tide ranges round E.uropa

Point,