MISCELLANEOUS TRACTS.

[TRANSLATED FROM THE LATIN.]

OF THE EBB AND FLOW OF THE SEA.

The investigation of the causes of the ebb and which return at regular periods of the year. That flow of the sea, attempted by the ancients and in consequence of these and similar causes, they then neglected, resumed by the moderns, but vary their states of flow and eddy, both as relates rather frittered away than vigorously agitated in to extending and widening the motion itself, and a variety of opinions, is generally, with a hasty to the velocity and measure of the motion ; and anticipation, directed to the moon, because of thus produce what we term currents. Thus, in certain correspondences between that motion, and the seas the depth of the basin or channel, the the motion of that orb. But to a careful inquirer occurrence of whirlpools or submarine rocks, the certain traces of the truth are apparent, which curvature of the shore, gulfs, bays, the various may lead to surer conclusions. Wherefore, to position of islands, and the like, have great effect, proceed without confusion, we must first distin-acting powerfully on the waters, their paths, and guish the motions of the sea, which, though agitations in all possible directions, eastward and thoughtlessly enough multiplied by some, are in westward, and in like manner northward and reality found to be only five; of these one alone southward; wherever, in fact, such obstacles, is eccentric, the rest regular. We may mention open spaces, and declivities exist in their respectfirst the wandering and various motions of what ive formations. Let us then set aside this parare called currents : the second is the great six- ticular, and, so to speak, casual motion of tho hours motion of the sea, by which the waters waters, lest it should introduce confusion in the alternately advance to the shore, and retire twice inquisition which we now pursue

For no one a day, not with exact precision, but with a varia- can raise and support a denial of the statement tion, constituting monthly periods. The third is which we are presently to make, concerning the the monthly motion itself, which is nothing but a natural and catholic motions of the seas, by cycle of the diurnal motion periodically recurring: opposing to it this motion of the currents, as not the fourth is the half-monthly motion, formed by at all consistent with our positions. For the curthe increase of the tides at new and full moon, rents are mere compressions of the water, or more than at half-moon: the fifth is the motion, extrications of it from compression: and are, as once in six months, by which, at the equinoxes, as we have said, partial, and relative to the local the tides are increased in a more marked and form of the land or water, or the action of the signal manner.

winds. And what we have said is the more It is the second, the great six-hours or diurnal necessary to be recollected and carefully noted, motion, which we propose for the present as the because that universal movement of the ocean of principal subject and aim of our discourse, treat-which we now treat is so gentle and slight, as to ing of the others only incidentally and so far as be entirely overcome by the impulse of the curthey contribute to the explanation of that motion. rents, to fall into their order, and to give way, be

First, then, as relates to the motion of currents, agitated, and mastered by their violence. That there is no doubt that to form it the waters are this is the case is manifest particularly from this either confined by narrow passages, or liberated fact, that the motion of ebb and flow, simply, is by open spaces, or hasten as with relaxed rein, not perceptible in midsea, especially in seas down declivities, or rush against and ascend ele- broad and vast, but only at the shores.

It is, vations, or glide along a smooth, level bottom, or therefore, not at all surprising, that, as inferior are ruffied by furrows and irregularities in the in force, it disappears, and is as it were annihichannel, or fall into other currents, or mix with lated amidst the currents; except that where the them and become subject to the same influences, currents are favourable, it lends them some aid or are affected by the annual or trade winds, and impetuosity, and, on the contrary, where they are adverse considerably restrains them. Waiving and supply its place. If there were

a fresh then the motion of the currents, we proceed to the quantity of water added, it must be by flowing four regular motions; that in the six hours, in the and eruption from the earth. If there were dilatamonth, in the half month, and in six months, of tion only, this must take place either by solution which the sexhorary motion alone seems to pro- into greater rarity, or by a tendency to approach duce and develope the ordinary tide, the monthly another body, which, as it were, evokes the to determine that motion and define its renewal; waters, attracts them, and lists them to greater the half-monthly and half-yearly to increase and elevation. And, doubtless, that state of the strengthen it. For the ebb and flow, which cover waters, whether considered as ebullition, or rareand quit again a certain extent of shore, both vary faction, or harmony with some one or other of the at various hours, and according to the momentum heavenly bodies, cannot seem incredible, that is, and quantity of the water; whence these three to a moderate extent, and on the supposition of the other motions are rendered more perceptible. lapse of considerable time, in which such swell.

We must, therefore, contemplate, singly and ings and accretions may gather and accumulate. specifically, as we purposed, the motion of ebb Therefore the difference observable between the and flow. And, first, it is necessary to grant that ordinary, and the half-monthly tide, or the most this motion, the subject of inquiry, is one of these copious of all, the half-yearly one, in which the two: either the motion of an elevation and depres- addition to the mass of waters is nct equal 10 sion, or the motion of a progression of the waters. the difference between ordinary ebb and flow, and The motion of elevation and depression we under- has besides a large interval of time insensibly to stand to be such, as is found in boiling water, form, may, on the hypothesis of clevation and mounting and subsiding alternately in a caldron : depression, be consistently explained. But that the motion of progression to be such as is ob- so great a mass of water should burst forth as to served in water carried in a basin, which quitting explain that difference which is found between the one side, is projected to the opposite. Now, the ebb and flow, and that this should take place that the motion we treat of is not of the former with such extreme rapidity, namely, twice a day, sort, is in the first place suggested by this fact, as if the earth, according to the fantastic notion that in different parts of the world the tides vary of Apollonius, performed respiration, and breathed according to the times, so that in certain places waters every six hours, and then again inhaled there are floods and accumulations of the mass them, is very hard to believe. And let no man of waters, in others at the same hours ebb and be misled by the unimportant fact that in some diminutions. Now, the waters, if they did not places wells are said to have a simultaneous motravel from place to place, but rose ebullient from tion with the ebb and flow of the sea, whence one the bottom, ought to rise everywhere at once, might conjecture, that waters enclosed in the and to subside together. For we see those two entrails of the earth boil up in like manner, in other motions, the monthly and half monthly, in which case that swelling of the waters cannot be full movement and operation at the same periods attributed to a progressive motion. For the anthroughout the globe. For the waves increase swer is an easy one, that the flow of the sea by at the equinoxes in all parts, not in certain places its encroachment may perforate and gorge many under the equator, or in others under the tropics: hollow and loose places of the earth, turn the and the same is true of the half-monthly motion. course of subterraneous waters, or cause a rever. For, everywhere over the world, the waters are beration of the enclosed air, which by a continued elevated at new moon and full moon, nowhere at series of impulsions may raise the water in this half-moon. The waters, therefore, are manifestly sort of wells. Accordingly, this does not take raised, and again depressed in these two motions, place in all wells, nor even in many, which ought and like the heavenly bodies have their apogees to be the case if the entire mass of waters had a and perigees. But in the ebb and flow of the property of periodically boiling up, and a harmony sea, which we now discuss, the contrary takes with the tide. But, on the contrary, this rarely place, an unequivocal sign of progressive motion. happens, so as to be regarded almost as a miracle, Besides, ere we set down the flow of the sea as because, in fact, such apertures and spiracles as an elevation of the waters, we ought to consider reach from wells to the sea, without circuity or a little more carefully how that elevation can take impediment, are very rarely found; nor is it unplace. For the swelling must either be produced important to mention, what some relate, that in by an augmentation of the mass of waters, or deep pits situated not far from the sea, the air from an extension or rarefaction of fluid in that becomes thick and suffocating at the time of ebb, inass, or from simple elevation of the mass or from which it may seem manifest, not that the body. The third supposition we must dismiss waters boil up, (for none are seen to do so,) but entirely. For if the water united in the same that the air is reverberated. No doubt, there is body were lifted up, a vacuum would necessarily another objection, not despicabie, but of great he left between the earth and the under face of weight, every way deserving of an answer, one the water, there being no body ready to succeed / which had been the subject of careful observation,

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and that not incidentally, but a thing especially bodies. Notwithstanding, it will not immediand of purpose inquired into and discovered, ately follow from this, and we would have men namely, that the water at the opposite shores of note the observation, that those things which Europe and of Florida ebb at the same hours agree in their periods and curriculum of time, '. from both shores, and do not quit the shore of even in their mode of relation, are of a nature Europe when they roll to the shore of Florida, subjected the one to the other, and stand respectlike water (as we have said before) agitated in a ively as cause and effect. Thus we do not go so basin, but are manifestly raised and depressed at far as to affirm, that the motions of the sun ought either shore at once. But a clear solution of this to be set down as the causes of the inferior moobjection will be seen in the observations which tions which are analogous to them; or that the shall presently be made about the path and pro- sun and moon (as is commonly said) have domigression of the ocean; the substance, however, nion over these motions of the sea, although such is this; that the waters, setting out in their course notions are easily insinuated into our minds from from the Indian ocean, and obstructed by the veneration of the heavenly bodies; but in that remora of the continents of the old and new very half-monthly motion, if it be rightly noted, world, are impelled along the Atlantic from south it were a new and surprising kind of subjection to north; so that it is no wonder if they are driven to influence, that the tides at new and at full against either shore equally at the same time, as

moon should be affected in the same manner, waters are wont to be, which are propelled from when the moon is affected in contrary ways; and the sea into estuaries and up the channels of many other things might be instanced, destroying rivers, evidently showing that the motion of the similar fancies of this sort of dominant influence, sea is progressive as respects the rivers, and yet and leading to this inference, that those corresthat it at once inundates both shores. Notwith-pondences arise from the catholic affections of standing, according to our custom we freely con- matter, from the primary concatenation of causes, fess, and would have men observe and remember, and connexion of things; not as if such were that if it is found in experience that the tide ad-governed the one by the other, but both flowed vances at the same time on the coast of China from the same sources and from joint causes. and Peru, as on that of Europe and Florida, this Notwithstanding this, however, it remains true, our opinion, that ebb and flow is a progressive as we have said, that nature delights in harmony, motion of the sea, must be repudiated.

and scarcely admits of any thing isolated or soliFor if the flow of the sea takes place at the tary. We must therefore look, in treating of the same time at the opposite shores, as well of the sexhorary ebb and flow of the sea, with what Pacific or Southern Ocean as of the Atlantic other motions it is found to agree and harmonize. Ocean, there are not in the universe any shores And first we must inquire with respect to the remaining, at which a corresponding ebb, at the moon, in what manner that motion blends relasame time, might afford a satisfactory solution of tions or natures with the moon. But this we do the objection. But we propose with confidence not see prevail except in the monthly repairing of a trial of this by experiment, to whose test we of the moon, for the periodical course of six hours submit our cause: for we are clearly of opinion, has no affinity with the monthly course ; nor again that were the general result of a trial of this fact are the tides found to follow any affections of the through the world known to us, this compaet of moon.

For, whether the moon be crescent or nature would be found effected on sufficiently waning, whether she be under the earth or above reciprocal conditions, namely, that at any given the earth, whether her elevation above the horizon hour as much reflux took place in some parts of be higher or lower, whether her position be in the the world as flow in others. Therefore, from what zenith or elsewhere, in none of these relations do we have stated, this motion of ebb and flow may the ebb and flow of the tide correspond with her. be affirmed progressive.

Therefore, leaving the moon, let us inquire Now follows the inquiry, from what cause and concerning other correspondences; and from all what combination of things this motion of ebb the motions of the heavenly bodies, it is certain and flow arises and is presented to view. For all that the diurnal motion is the shortest, and is the great movements (if these be regular and per- accomplished in the least period of time, that is, petual) are not isolated, or (to use here an expres- in the space of twenty-four hours. It is therefore sion of the astronomers) ferine, but have some in harınony with this, that the motion of which thing in nature with which they move harmoni- we inquire, which is yet three times shorter than ously. Therefore those motions, as well as the the diurnal one, should be referred immediately half-monthly one of increase as the monthly of to that motion which is the shortest of the reparation, appear to accord with the motion of the heavenly ones.

But this notion has no great moon; and again the half-monthly, or equinoctial, weight with us in this matter. Another hypowith the motion of the sun; also the elevations thesis has more influence with us, that this motion and depressions of the water, with the approxi- is so distributed, that, though the motion of the mation and revolution in the orbits of the heavenly' waters is slower by innumerable degre-s, still it

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is referable to a common measure. For the space and with the same conversion : but in the tropies of six hours is a quarter of the diurnal motion, they are not generally so confined, nor move in which space (as we said) is found in that motion the regular course, but sometimes straggle toof the sea, with a difference coinciding with the wards the poles, yet, nevertheless, pursue their measure of the moon's motion. Whereupon this rotatory motion from east to west. And thus this belief sinks deep into our mind, and looks as it motion, though it suffers great diminution, since were an oracular truth, that this motion is of the the nearer it descends towards earth the consame kind with the diurnal motion. With this, version is performed in smaller circles, and more therefore, as a basis, we shall proceed to a slowly, still remains powerful, so as to traverse thorough inquiry: and we think that the whole great distances in a short time. For these comets subject is exhausted in three points of investi- are carried round the whole circumference, both gation.

of the earth and the lower atmosphere, in the The first is, whether that diurnal motion is con- space of twenty-four hours, with an excess of fined within the regions of heaven, or descends, one or two hours more. But after, by a continued and penetrates to the lower parts? The second descent, it has reached these regions upon which is, whether the seas move regularly from east to the earth acts, this motion, not only by the com. west, as the heaven does? The third, whence and munication of the earth's nature and infuence, how that six hours' motion of the tides takes place which represses and lowers circular motion, but which coincides with a quarter of the diurnal mo- also by a substantial immission of the particles tion, with a difference falling in with the measure of its matter, by means of vapours and gross ex. of the moon's motion. Now, as relates to the halations, becomes infinitely relaxed, and almost first inquiry, we think that the motion of rotation, falls off, yet it is not therefore wholly annihilatec or of turning from east to west, is not properly a or ceases, but remains feeble and verging to imper. inotion merely of the heavenly bodies, but mani- ceptible. For mariners now begin to confess that festly of the universe, and a primary motion in all between the tropics,where, in the open sea, the mothe great fluids, found to prevail from the highest tion of the air is best perceived ; and where the air part of heaven to the lowest part of the waters, itself, as well as heaven, revolves in a larger circle, in direction the same in all, in impulse, that and therefore more rapidly, that a perennial and is, in rapidity and slowness, widely different; in gentle breeze blows from east to west, insomuck such wise, however, that in an order not in the that those who wish to use the south-west wind least confused, the rapidity is diminished in propor- often seek and avail themselves of it outside the tion as the bodies approach the globe of the earth. tropics. Consequently, this motion is not extinNow this, it seems, may be taken as a probable guished, but becomes languid and obscure, so as to reason for supposing that that motion is not be scarcely perceptible outside the tropics. Yet, limited to the heavens, because it prevails and is even outside the tropics, in our own part of the in force through so great a depth of heaven as globe, Europe, at sea, in serene and peaceful lies between the starry heaven and the moon, weather, there is observed a certain wind, which (a space much more extensive than that between is of the same species; we may even conjecture the moon and the earth,) with a regular diminution; that what we experience here in Europe, where so that it is probable that nature does not at any the east wind is sharp and dry, and, on the conpoint abruptly break off a harmonious motion of trary, the south-west winds are cherishing and huthis kind, diffused through such vast spheres and mid, does not depend merely on the circumstance gradually lessening. And that this is so in the that the one blows from a continent, the other from heavenly bodies is evinced by two inconsistencies, the ocean, but on this, that the breath of the east which follow from the opposite hypothesis. For, wind, since it is in the same train with the proper since the planets visibly perform a diurnal motion, motion of the air, accelerates and heightens that unless we are to suppose that motion natural and motion, and therefore disperses and rarefies the self-moved in all the planets, we must unavoida- air, but that of the west wind, which is in the bly have recourse for an explanation either to the contrary direction to the motion of the air, makes it supposition of the primum mobile, which is evi- rebound upon itself, and become inspissated. Nor dently opposed to nature; or to the rotation of ought this to be neglected, which is admitted the earth, which is a notion extravagant enough, into the number of common observations, that if we look to the methods of nature. Therefore, the clouds which are in motion in the upper part the motion exists in the heavenly bodies. And, of the air generally move from east to west; qnitting heaven, that motion is most distinctly while the winds about the earth's surface gene. visible in the inferior comets; which, though rally blow at the same time the contrary way. Inwer than the orb of the moon, evidently move And if they do not this always, the reason is from east to west. For, though they have their this, that there are sometimes opposite winds, solitary and eccentric motions, yet in performing some acting on the high, others on the lowest them they for a time have a common movement, exhalations. Now, those blowing on high, if and are borne along with the motion of the ether, they be adverse, confound the real motion of the

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air. It is sufficiently clear, then, that the motion ing, and reverberated by the interposition of lands, is not confined within the limits of heaven. which extend both ways longitudinally from

Then follows in order the second inquisition : south to north; and nowhere but toward their whether the waters move regularly from east to extremities afford a free canal to the waters. But west. Now, when we speak of waters, we mean that strong direction of the waters, which is those accumulations or masses of waters which caused by the Indian Ocean towards the north, are such large portions of nature as to have a and in the opposite direction from the North Sea relation of harmony to the fabric and system of towards the South, differ infinitely in the extent of the universe. And we are fully of opinion that sea, affected on account of the different force aná the same motion is natural to, and inherent in, quantity of waters. But that this should take the body of waters, but is slower than in the air; place is unavoidable. For the two great islands though, on account of the grossness of the body, of the old and new world have the same figures, it is more palpable and manifest. Of this we and are so stretched out as to broaden to the north, shall content ourselves with three selected from and taper to the south. The seas, therefore, on many experimental proofs, but these weighty and the contrary, towards the south occupy a vast marked ones, which prove that this is so. space, but to the north a small one, at the back of

'The first is, that there is found a manifest mo- Asia, Africa, and America; consequently, that tion and flow of waters from the Indian Ocean, great mass of waters which is discharged from even to the Atlantic, and that more swift and the Indian Ocean, and is refracted into the Atlanstrong towards the Straits of Magellan, when an tic, is capable of forcing or propelling the course outlet is opened to them westwards; and a great of the waters in a continued movement nearly to current also on the other side of the world from the British Sea, which is a part of the line dethe Northern Ocean to the Briti:Sea. And these scribed northwards. But that much smaller porcurrents of waters manifestly roll from east to tion of the waters which issues from the north west; in which fact we must note in the first sea, and which has also a free

passage westwards place, that in those two places alone the seas find at the back of America, is not strong enough to thoroughfares, and can describe in flowing a com- turn the course of the waters southwards, except plete circle: whereas, on the contrary, at the cen- towards that point which we mentioned, namely, tral regions of the globe, by the two ramparts of about the British Sea. Now, in these opposite the old and new world, they are thrown off and currents, there must be some goal where they driven (as it were into the estuaries of rivers) into meet and contend, and where within short space the basins of the Atlantic and Pacific, the two the order of advance is suddenly changed, as we oceans extending between the south and north, have said occurs about Graveling—the focus of and

open to the motion of a current from east to the currents from the Indian and Northern Oceans, west. So that the true course of the waters is and that a certain ocean stream is formed by opinost safely inferred from the extremities of the posite currents on the coast of Holland has been globe, as we have stated, where they meet with noted by numbers, not only from the inversion of no impediment, but sweep round in full circuit. the hour of the tide, which we have stated, but And the first experiment is thus, the second is the also from the peculiar visible effect. Now, if this following.

is so, we return to the position, that it must needs Let us suppose that the tide takes place at the be, that in proportion as the parts and shores of mouth of the Straits of Gibraltar at any given the Atlantic extend southwards and approach the hour: it is certain that the tide sets in at Cape Indian Sea, in the same proportion the tide is St. Vincent later in the day than at the mouth of prior, and early in the order of approach, and in the Straits—at Cape Finisterre later than at Cape proportion as you go northwards, (as far as their St. Vincent,-at King's Island later than at Cape common goal,) where they are forced back by the Finisterre,—at the Island Heek later than at antagonist stream of the Northern Ocean, they are King's Island,-at the entrance of the English backward and late. Now, that this is the case, channel later than at Heek,—at the shore of Nor. the observation of the progression from the Straits mandy later than at the entrance of the channel. of Gibraltar to the British Sea manifestly proves. Thus far in regular order: but at Graveling, as if Wherefore we think that the tide about the shores by an entire inversion of the order, and that with of Africa is at an earlier hour than that of the a great leap, as it were, at the same hour, with a Straits of Gibraltar, and, in reversed order, the tide velocity like that which it has at the mouth of the about Norway earlier than the tide about Sweden-Straits of Gibraltar. This second observation we but this we have not ascertained by experiment or apply to, and compare with the first. For we testimony. think, as has already been said, that in the Indian A third experiment is the following: The seas and northern oceans the true currents of the confined by land on one side, which we call bays, waters, that is, from the east to the west, are open if they stretch out with any inclination from east and unimpeded, but in the channels of the At- to west, which is in the same line of impetus lantic and Southern Oceans imprisoned and cross- with the true motion of the waters, have heavy