CURIOSITIES RESPECTING THE SEA.

General Observations Respecting the Sea, or Ocean.

The sea, or ocean, is that vast tract of water which encompasses the whole earth. What proportion the superficies of the sea bears to that of the land, is not precisely known, though it is said to be somewhat more than two-thirds. As the waters of the earth must necessarily rise to the surface thereof, it being specifically lighter than the earth, it was necessary there should be large cavities therein, as receptacles to contain them, otherwise they would have overspread all the surface of the earth, and so have rendered it utterly uninhabitable for terrestrial animals: it is well known, that the centre of the earth is the common centre of gravity, and that the nature of fluids is such, that they equally yield to equal powers; hence it follows, that where the power of attraction is every where the same at equal distances from the centre, the superficial parts of the water will every where conform themselves to this attractive power, at an equidistant situation from the centre, and, it is evident, will form the surface of a sphere, so far as they extend. The reason then that the sea seems higher than the land, results from the fallacy of vision, whereby all objects, whether on the land or sea, appear higher as they become more distant: and the reason will be plain to those who are acquainted with optics; for it is well known, that the denser any medium is, through which we behold objects, the greater is the refraction, or the more their images appear above the horizontal level; while the greater the quantity of medium through which the rays pass, the more they will be bent from their first direction: on both these accounts, the appearances of things at a great distance, both on the land and the sea, will be somewhat above the horizon, and the more so as they are the more remote.

With regard to the depth or profundity of the sea, Varenius affirms, that it is in some places unfathomable, in other places very various, being from fifty yards to four and a half English miles, in some places deeper, and that the depth is much less in bays than in oceans. In general, the depths of the sea bear a great analogy to the height of mountains on the land, so far as discoveries have hitherto extended. It is a general rule among sailors, and is found to hold true in many instances, that the more the shores of any place are steep and high, forming perpendicular cliffs, the deeper the sea is below; and that, on the contrary, level shores denote shallow waters. Thus, the deepest part of the Mediterranean is generally allowed to be under the heights of Malta. And the observation of the strata of earth and other fossils, on and near the shores, may serve to form a good judgment as to the materials to be found in the bottom of the sea; for the veins of salt and bitumen doubtless run on in the same order as we see them on the shore. If we may reason from analogy, the strata of rocks, that serve as a foundation for hills and elevated places on shore, serve also, in the same continued chain, to support the immense quantity of water in the basin of the sea.

The coral fisheries have given occasion to observe, that there are many, and those very large caverns or hollows in the bottom of the sea, especially where it is rocky, and that the like caverns are sometimes found in the perpendicular rocks which form the steep sides of those fisheries. These caverns are often of great depth as well as extent, and have sometimes wide mouths, and sometimes only narrow entrances, into large and spacious hollows.

The bottom of the sea is covered with a variety of materials, such as could not be imagined by any but those who have examined into them, especially in deep water, where the surface only is disturbed by tides and storms; the lower part, and consequently its bed at the bottom, remaining, for ages perhaps, undisturbed. The soundings, when the plummet first touches the ground, on approaching the shores, give some idea of this. The bottom of the plummet is hollowed, and in that hollow there is placed a lump of tallow, which is the first part that touches the ground; and the soft nature of the fat receives into it some part of those substances which it meets with at the bottom: the substances thus brought up, are sometimes pure sand, sometimes a kind of sand made of the fragments of shells beaten to a sort of powder, sometimes they are composed of a like powder to the several sorts of corals, and sometimes they are composed of fragments of rocks; but besides these appearances, which are natural enough, and are what might well be expected, it brings up substances which are of the most beautiful colours.

Dr. Donati, in an Italian work, containing an essay on a natural history of the Adriatic Sea, has related many curious observations on this subject: having carefully examined the soil and productions of the various countries that surround the Adriatic Sea, and compared them with those which he took up from the bottom of the sea, he found that there was very little difference between the former and the latter. At the bottom of the water there are mountains, plains, valleys, and caverns, similar to those upon land. The soil consists of different strata, placed one upon another, and mostly parallel and correspondent to those of the rocks, islands, and neighbouring continents. They contain stones of different sorts, minerals, metals, various petrified bodies, pumice stones, and lavas formed by volcanoes. One of the objects which most excited his attention, was a crust, which he discovered under the water, composed of crustaceous and testaceous bodies, with beds of polypes of different kinds, confusedly blended with earth, sand, and gravel: the different marine bodies, which form this crust, are found at the depth of a foot or more, entirely petrified, and reduced into marble; these, he supposes, are the natural beds of the sea, and not made so by means of volcanoes and earthquakes, as some have conjectured. On this account, he imagines that the bottom of the sea is constantly rising higher and higher, with which other obvious causes of increase concur; and from this rising of the bottom of the sea, that of its level or surface naturally results; in proof of which, this writer recites a great number of facts.

M. Dassie has been at great pains to prove, that the sea has a general motion, independently of winds and tides, and that it is of more consequence in navigation than is generally supposed. He affirms, that this motion is from east to west; inclining towards the north, when the sun has passed the equinoctial northward, during the time he is passing through the northern signs; but the contrary way, after the sun has passed the said equinoctial southward: adding, that when this general motion is changed, the diurnal flux is changed also; whence it happens, that in several places the tides come in during one part of the year, and go out during the other, as on the coasts of Norway, in the Indies at Goa, Cochin-china, &c. where, while the sun is in the summer signs, the sea runs to the shore; and when in the winter signs, runs from it. On the most southern coasts of Tonquin and China, for the six summer months, the diurnal course runs from the north with the ocean; but the sun having repassed the line toward the south, the course declines also southward.

There are two principal reasons why the sea does not increase by means of rivers, &c. falling every where into it. The first is, because waters return from the sea by subterranean cavities and aqueducts, through various parts of the earth. Secondly, because the quantity of vapours raised from the sea, and falling on the land, only cause a circulation, but no increase of water. It has been found, by calculation, that in a summer’s day there may be raised in vapours, from the Mediterranean Sea, 5,280,000,000 tons of water, and yet this sea receiveth not, from all its nine great rivers, above 1,827,000,000 tons per day, which is but a third part of what is exhausted in vapours.

The ascent of the sea for the formation of springs, by a subterranean circulation of its water to their sources, has been a great objection, with many, against the system which ascribes their origin to the ocean; but Dr. Plot has observed, that there are many ways by which the water may ascend above its own level: 1. By the means of subterranean heat. 2. By filtration. 3. By the unequal height of several seas. 4. By the distance of the centre of magnitude from the centre of gravity in the terraqueous globe; the superficies of the Pacific Sea being said to be further from the centre of gravity than the top of the highest hill on the adverse part of the globe. And, 5. By the help of storms. The sea water actually ascends above its own level, and finds its way into wells, whose bottoms lie higher than the surface of the sea at high-water mark.

We shall now enter more particularly on The Curiosities of the Sea.—For the following observations we are principally indebted to Sturm.

“Instead of regarding the sea as an object of terror, let us consider the wonders and the benefits which it presents to us. It must be granted that when the waves swell into mountains, and the tempest roars, its aspect is terrific; and we must be hardy indeed, not to consider it as a most formidable element in such times of awful visitation, when ships, breaking from their anchor, or driven from their course, rush before the winds that beat upon them with ungovernable fury, till, dismasted, and their rigging shivered in fragments, they sink, overwhelmed with a weight of waters, or strike some sand-bank, or shelving rock, and are at once dashed to pieces. Sometimes whirlpools, or vast masses of water with a violently circular motion, whirl the unfortunate vessel that fate urges into their vortex, with irresistible force, till the helpless victim sinks an easy prey to the tremendous gulf, and the cries of the unfortunate wretches are lost in the roar of the waves: these whirlpools are occasioned by rocks in the ocean, and the meeting of numerous currents and eddies. Not less dangerous are the waterspouts, that the wind raises from the sea to the clouds; they hover in the air high above the ocean, and the wind whirls them round with violence. They often burst with a great crash, and occasion much mischief; for if they fall upon a vessel, they destroy its rigging, and sometimes sink it to the bottom.

“But it would be highly unjust and ungrateful, only to consider the losses occasioned by the sea, without reflecting upon the magnificent and stupendous works of God, and that goodness which even visits the unfathomable depths of the ocean. The first thing that strikes us, upon the investigation of sea water, is its saltness; a pound of the water containing about two ounces of salt. Sea salt appears lighter than that we commonly use, and yet it is not attracted by the air, nor lessened by the continual influx of fresh water; the cause of this is unknown. If this peculiar quality arose from mountains of salt contained in the sea, it would be salter in some places than in others, of which we have no proof. But whatever is the occasion of this saline property of the sea, it is absolutely necessary to accomplish certain ends. It is that which preserves such a vast body of water from corruption, and renders it capable of supporting a greater weight. The colour of sea water is also deserving of attention: it is not every where alike, which perhaps arises in part from its reflecting the colour of the bottom and that of the sky. It often appears dark and black in deep abysses, white and foaming during a storm, silvery, and gilded with reflections of the most beautiful hue, when the last rays of the setting sun play upon the unruffled surface: the colour of the sea, in addition to these, varies, from numberless insects, marine plants, and the combination of the different substances which the rivers and torrents carry with them into the ocean. When it is calm, and not a breeze skims over its bosom, it sometimes glitters with the most brilliant stars; and the track of a ship cleaving the waves has often a luminous appearance, like a river of fire.

“The creatures which inhabit the sea excite our surprise and admiration; we there discover a new world, and the number of beings which compose it is prodigious. Aquatic animals are not so numerous in their species as the land animals; but they surpass them in size and duration. The elephant and ostrich yield in bulk to the whale, the largest fish of the ocean, its length being often from sixty to seventy feet; and no land animal can vie with it in longevity, for it lives as long as the oak. If we may rely upon certain accounts, there are creatures in the ocean, far exceeding the size of the whale; as the animal called kraken, said to exist in the northern seas, and whose circumference is half a German league. Who is able to number the different species of animals which people the seas? or who can determine their form, structure, size, and properties? How infinitely great is that God who has created the sea! will be the conclusion of all who investigate the subject, and it is not without the wisest reasons that the Creator has made the ocean and the seas to occupy two-thirds of the whole globe. The seas were designed not only to form great reservoirs of water, but by means of their evaporation to be the sources of rain, snow, and various meteors. What wisdom is displayed in the connection which the seas have with each other, and in their continual motion! And it is not less wonderful that the bottom of the ocean is of the same nature as the surface of the earth. There are found in the sea, rocks, caverns, plains, springs, plants, and animals; and the islands are only the summits of a long chain of mountains. When we consider that the seas form a part of the globe the least investigated, we are disposed to believe that they contain many more wonders, which neither the senses nor the understanding of man can penetrate, while all acknowledge the adorable wisdom and power of the Most High. To Him then, who has established the monuments of his grandeur and the sceptre of his glory in the ocean, as upon the earth, be ascribed all admiration and praise!”

The following opinions of a late celebrated philosopher and divine, on the Saltness of the Sea, may not be unacceptable to our readers:—“There are few questions, (observes Bishop Watson,) respecting the natural history of our globe, which have been discussed with more attention, or decided with less satisfaction, than that concerning the primary cause of the saltness of the sea. The solution of it had perplexed the philosophers before the time of Aristotle; it surpassed his own great genius; and those of his followers, who have attempted to support his arguments, have been betrayed into very ill-grounded conclusions concerning it. Father Kircher, after having consulted three and thirty authors upon the subject, could not help remarking, that the fluctuations of the ocean itself were scarcely more various than the opinions of men concerning the origin of its saline impregnation. The question does not seem capable of admitting an illustration from experiment; at least no experiments have hitherto been made for that purpose, and therefore we may be the less surprised at its remaining nearly as problematical in the present age, as it has been in the preceding. Had there, indeed, been any observation made three or four centuries ago, ascertaining the saltness of the sea at any particular time and place; we might, by similar observations at the same place and the same season, have been able to know whether the saltness at that particular place was an increasing, decreasing, or an invariable quantity; and this kind and degree of knowledge would have served as a clue to direct us to a full investigation of this matter in general; but it is to be regretted, that no such observations have, till very lately, been made with any tolerable precision.—There are three principal opinions on this subject, which have been maintained by philosophers of modern date; some, observing that river water, almost in every part of the globe, is in a greater or less degree impregnated with sea salt, have thought that the sea has gradually acquired its present quality of salt from the long-continued influx of rivers.”

Other philosophers, observing that large beds of fossil salt are not unfrequent in any quarter of the globe; and conceiving, with great probability, the bottom of the sea to be analogous in its formation to the surface of the earth, have undertaken to derive its saltness from the beds of rock salt, which they have supposed to be situated at its bottom; and they are further of opinion, that without such a permanent saline principle, the sea would long since have become insipid from the fresh water poured into it by an infinity of rivers. Strange! that what, according to the fore-mentioned hypothesis, was thought sufficient to account for the saltness of the sea, should in this be esteemed instrumental in annihilating the saltness already supposed to exist.

Boyle unites, as it were, and takes the two preceding hypotheses, and imagines the saltness of the sea to be supplied, not only from rocks and other masses of salt, which at the beginning were, and in some countries may yet be found, either at the bottom of the sea, or at the sides, where the water can reach them, but also from the salt which the rivers, rains, and other waters, dissolve in their passage through divers parts of the earth, and at length carry with them into the sea. Buffon, and the generality of philosophers, acquiesce in the opinion of Boyle.—“After all, (says he,) it may be observed, that we are inquiring into the cause of a phenomenon, which it may be said had no secondary cause at all. It is taken for granted, in this disquisition, that the water which covered the globe in its chaotic state, was not impregnated with salt as at present, but quite fresh: now this is an opinion concerning a matter of fact, which can never be proved either way; and surely we extend our speculations very far, when we attempt to explain a phenomenon, primeval to, or coeval with, the formation of the earth.”

This sensible writer then states the different experiments which have been made to discover the saltness of the sea, round the shores of Britain; and proposes the following simple method of ascertaining it with tolerable certainty:—

“As it is not every person who can make himself expert in the use of common means of estimating the quantity of salt contained in sea water, I will mention a method of doing it, which is so easy and simple, that every common sailor may understand and practise it; and which, at the same time, from the trials I have made of it, seems to be as exact a method as any that has yet been thought of.—Take a clean towel, or any other piece of cloth; dry it well before the sun or before the fire, then weigh it accurately, and note down its weight; dip it in the sea water, and, when taken out, wring it a little till it will not drip when hung up to dry; weigh it in this wet state, then dry it in the sun or at the fire, and when it is perfectly dry, weigh it again: the excess of the weight of the wetted cloth above its original weight, is the weight of the sea water imbibed by the cloth; and the excess of the weight of the cloth after being dried, above its original weight, is the specific gravity of the salt retained by the cloth; and by comparing this weight with the weight of the sea water imbibed by the cloth, we obtain the proportion of salt contained in that species of sea water.”

Whoever undertakes to ascertain the quantity of salt contained in sea water, either by this or any other method, would do well to observe the state of the weather preceding the time when the sea water is taken out of the sea; for the quantity of salt contained in the water near the surface, may be influenced, both by the antecedent moisture, and the antecedent heat of the atmosphere. And this leads to the consideration of a question proposed by Aristotle,—Why are the upper parts of the sea salter and warmer than the lower? Some philosophers, admitting the fact, have followed him in attempting to explain it; whilst others have thought themselves authorized by experiment to deny the truth of the position; and those, perhaps, will argue with the greatest justness, who shall affirm that it is neither generally to be admitted, nor generally to be rejected, but that the sea in some places, and under certain circumstances, is salter and warmer at the surface, than at any considerable depth beneath it, while in many others the reverse is true. The question consists of two parts, betwixt which, though there probably is a connection, yet it is not so necessary a one as to hinder us from considering each part by itself.

With regard to the use of this salt property of sea water, it is observed, that the saltness of the sea preserves its waters pure and sweet, which otherwise would corrupt, and emit a stench like a filthy lake, and consequently that none of the myriads of creatures which now live therein could exist. From thence also the sea water becomes much heavier, and therefore ships of greater size and burden are safely borne thereon. Salt water also does not freeze so soon as fresh water, hence the seas are more free for navigation.

We shall now make a few observations on The Tides:—

Say, why should the collected main
Itself within itself contain?
Why to its caverns should it sometimes cree
And with delighted silence sleep
On the lov’d bosom of its parent deep?
Why should its num’rous waters stay
In comely discipline and fair array,
Till winds and tides exert their high commands?
Then prompt and ready to obey,
Why do the rising surges spread
Their op’ning ranks o’er earth’s submissive head,
Marching through different paths to different lands?
Prior.

The tides consist of two periodical motions of the waters of the sea, called the flux and reflux, or the flow and ebb. The cause of the tides is the attraction of the sun and moon, but chiefly of the latter; the waters of the immense ocean, forgetful, as it were, of their natural rest, move and roll in tides, obsequious to the strong attractive power of the moon, and weaker influence of the sun.

That the tides may have their full motion, the ocean in which they are produced ought to be extended from east to west 90°, or a quarter of a great circle of the earth, at least; because the places where the moon raises most, and most depresses the water, are at that distance from one another. Hence it appears, that it is only in the great oceans that such tides can be produced, and why, in the large Pacific ocean, they exceed those in the Atlantic. From this it is also obvious why the tides are not so great in the torrid zone, between Africa and America, where the ocean is narrower, as in the temperate zones on either side; and from this also, we may understand why the tides are so small in islands that are very far distant from the shore. It is manifest, that, in the Atlantic ocean, the water cannot rise on one shore, but by descending on the other; so that, on these shores, at an intermediate distance, it must continue at about a mean height between its elevation on the one, and descent on the other shore. As the tides pass over shoals, and run through streights into bays of the sea, their motion becomes more various, and their height depends on a great many circumstances. The tide that is produced in the western coast of Europe corresponds to the theory above described: thus, it is high water on the coast of Spain, Portugal, and the west of Ireland, about the third hour after the moon has passed the meridian; from thence it flows into the adjacent channels, as it finds the easiest passage. One current from it, for example, runs up by the south of England, and another comes in by the north of Scotland: they take a considerable time to move all this way, and it is high water sooner in the places to which they first come; and the tides even begin to fall at those places, while the two currents are yet going on to others that are further in their course. As they return, they are not able to raise a tide; because the water runs faster off than it returns, till by a new tide propagated from the ocean, the return of the current is stopped, and the water begins to rise again. The tide takes twelve hours to come from the ocean to London bridge, so that, when it is high water there, a new tide is already come to its height in the ocean, and, in some intermediate place, it must be low water at the same time.

In channels, therefore, and narrow seas, the progress of the tides may be, in some respects, compared to the motion of the waves of the sea. It may be observed, that when the tide runs over shoals, and flows upon flat shores, the water is raised to a greater height than in the open and deep oceans that have steep banks; because the force of its motion cannot be broken upon these level shores, till the water rises to a greater height. If a place communicates with two oceans, (or two different ways with the same ocean, one of which is a readier and easier passage than the other,) two tides may arrive at that place in different times, which, interfering with each other, may produce a greater variety of phenomena.

An extraordinary instance of this kind is mentioned at Bathsha, a port in the kingdom of Tonquin in the East Indies, of northern latitude 20° 50'. The day in which the moon passes the equator, the water stagnates there without any motion: as the moon removes from the equator, the water begins to rise and fall once a day; and it is high water at the setting of the moon, and low water at her rising. This daily tide increases for about seven or eight days, and then decreases for as many days by the same degrees, till this motion ceases when the moon has returned to the equator. When she has passed the equator, and declines towards the south pole, the water rises and falls again, as before; but it is high water now at the rising, and low water at the setting, of the moon.

We shall close this chapter with an account of the remarkable fact of Waves stilled by Oil.—This wonderful property, though well known to the ancients, as appears from the writings of Pliny, was for many ages either quite unnoticed, or treated as fabulous by succeeding philosophers, till Dr. Franklin again attracted the attention of the learned to this subject; though it appears, from some anecdotes, that seafaring people have always been acquainted with it. Mr. Pennant, in his British Zoology, vol. iv. under the article Seal, takes notice, that when these animals are devouring a very oily fish, which they always do under water, the waves above are remarkably smooth; and by this the fishermen know where to find them. Sir Gilbert Lawson, who served long in the army at Gibraltar, assured Dr. Franklin, that the fishermen in that place are accustomed to pour a little oil on the sea, in order to still its motion, that they may be enabled to see the oysters lying at its bottom, which are there very large, and which they take up with a proper instrument. A similar practice is followed among fishermen in various other parts; and Dr. Franklin was informed by an old sea captain, that the fishermen of Lisbon, when about to return into the river, if they saw too great a surf upon the bar, would empty a bottle or two of oil into the sea, which would suppress the breakers, and allow them to pass freely. The Doctor having revolved in his mind all these pieces of information, became impatient to try the experiment himself. At last, having an opportunity of observing a large pond very rough with the wind, he dropped a small quantity of oil upon it. But having at first applied it on the lee side, the oil was driven back again upon the shore. He then went to the windward side, and poured on about a tea-spoonful of oil; this produced an instant calm over a space several yards square, which spread amazingly, and extended itself gradually till it came to the lee-side; making all that quarter of the pond, perhaps half an acre, as smooth as glass. This experiment was often repeated in different places, and was always attended with success.