Part 56

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.

CHAP. XLV.

CURIOSITIES RESPECTING THE SEA.--(_Concluded._)

"--------------------Adoring, own The hand Almighty, who its channel'd bed Immeasurable sunk, and pour'd abroad, Fenc'd with eternal mounds, the fluid sphere; With every wind to waft large commerce on, Join pole to pole, consociate sever'd worlds, And link in bonds of intercourse and love Earth's universal family."

ON THE PERFECTION OF NAVIGATION.

The following account of the present wonderful perfection of navigation, is taken from a History of Voyages and Discoveries made in the North; translated from the German of John Reinhold Foster, LL.D.--

"Of all the arts and professions which have at any time attracted notice, none has ever appeared to be more astonishing and marvellous than that of navigation, in the state in which it is at present; an art which doubtless affords one of the most certain irrefragable proofs of the amazing powers of the human understanding. This cannot be made more evident, than when, taking a retrospective view of the tottering inartificial craft to which navigation owes its origin, we compare it to a noble and majestic edifice, containing 1000 men, together with their provisions, drink, furniture, wearing-apparel, and other necessaries, for many months, besides 100 pieces of heavy ordnance; and bearing all this vast apparatus safely, and as it were on the wings of the wind, across immense seas to the most distant shores. The following example may serve for the present to delineate at full length, as it were, the idea above alluded to. But first I must premise, that a huge unwieldy log of wood, with the greatest difficulty, and in the most uncouth manner, hollowed out in the inside, and somewhat pointed at both ends, and in this way set on a river for the purpose of transporting two or three persons belonging to one and the same family, across a piece of water a few feet deep, by the assistance of a pole pushed against the ground, cannot with any propriety be considered as the image of navigation in its first and earliest stage. For it seems evident to me, that people in the beginning only took three or four trunks of trees, and fastened them together, and then, by means of this kind of raft, got across such waters as were too deep for them to ford, and across which they could not well swim, with their children, and various kinds of goods which they might wish to preserve from being wet. The canoe, however, is a specimen of the art in a more advanced state, as this kind of craft is capable of having direction given to it, and even of so capital an improvement as that of having a sail added to it. For this reason I choose this vehicle for a standard, in preference to a mere raft, to which, imperfect as it is, it is so much superior.

"Let us, then, compare this with a large majestic floating edifice, the result of the ingenuity and labour of many hundreds of hands, and composed of a number of well-proportioned pieces, nicely fastened together by iron nails and bolts; and rendered so tight with tow and pitch, that no water can penetrate it. Now, in order to give motion and direction to this enormous machine, some astonishingly lofty pieces of timber have been fixed upright in it, and so many moveable cross pieces have been added to it, together with such a variety of pieces of strong linen cloth, for the purpose of catching the wind, and of receiving its impulse and propelling power, that the number of them amounts to upwards of thirty. For changing the direction of the yards and sails, according to particular circumstances, it has also been requisite to add a vast quantity of cordage and tackling; and nevertheless, even all this would not be sufficient for the perfect direction and government of the vessel, if there were not fastened to the hinder part of it, by means of hinges and hooks, a moveable piece of wood, very small indeed, in proportion to the whole machine, but the least inclination of which to either side is sufficient to give immediately a different direction to this enormously large mass, and that even in a storm, so that two men may direct and govern this swimming island with the same, or with greater ease, than a single man can do a boat. But if, besides, we consider, that, in a vessel like this, not a single piece is put in at random, but that every part of it has its determinate measure and proportion, and is fixed precisely in that place which is the most advantageous for it; that, throughout every part of it, there is distributed an astonishing quantity of blocks, stays, and pulleys, for the purpose of diminishing the friction, and of accelerating the motion of these parts; that even the bellying and vaulted part of the fabric, together with its sharp termination underneath, are proportioned according to the nicest calculations, and the most accurately determined rules; that the length and the thickness of the masts, the size of the booms and yards, the length, width, and strength of the sails and tackling, are all in due proportion to each other, according to certain rules founded upon the principles of motion: when we consider all this, I say, our admiration increases more and more at this great masterpiece of human power and understanding.

"Still, however, there are wanting a few traits to complete this description. A man in health consumes, in the space of twenty-four hours, about eight pounds of victuals and drink: consequently, 8000lb. of provisions are required daily in such a ship. Now, let us suppose a ship to be fitted out for three months only, and we shall find that she must be laden with 720,000lb. of provisions. A large forty-two pounder weighs about 6100lb. if made of brass, and about 5500lb. if iron; and generally there are twenty-eight or thirty of these on board a ship of 100 guns, the weight of which, exclusive of that of their carriages, amounts to 183,000lb.--on the second deck, thirty twenty-four pounders, each of which weighs about 5100lb. and therefore altogether 153,000lb.--the weight of the twenty-six or twenty-eight twelve-pounders on the lower deck, amounts to about 75,400lb.--that of the fourteen six-pounders on the upper deck, to about 26,600lb.--besides which, on the round tops, there are even three-pounders and swivels. Now, if to this we add, that the complete charge of a forty-two pounder weighs about 64lb. and that at least upwards of 100 charges are required for each gun, we shall find this to amount nearly to the same weight as the guns themselves. In addition to this, we must reflect, that every ship must have, by way of providing against exigencies, at least a second set of sails, cables, cordage, and tacklings, which altogether amount to a considerable weight. The stores, likewise, consisting of planks, pitch, and tow; the chests belonging to the officers and sailors; the surgeon's stores, and various other articles requisite on a long voyage; as also the small arms, bayonets, swords, and pistols, are no inconsiderable load; to which we must finally add the weight of the crew, which is not very trifling: so that one of these large ships carries at least 2162 tons burden, or 4,324,000lb. and at the same time is steered and governed with as much ease as the smallest boat. Now, the consideration of these circumstances alone, is sufficient to excite the most serious reflections in a contemplative mind; and yet, if such a ship sailed along the coast only, and never lost sight of the shore, as the navigators of old used to do, we might still be tempted to look upon navigation as an easy and trifling business. But the finding the straightest and shortest way over an ocean of more than sixty or eighty degrees in longitude, and thirty or forty in latitude; or across a track from 4000 to 6000 miles in extent, by day and by night, in fair weather or in foul; as well when the sky is overcast as when it is clear, and often with no other guide than the compass, and the being able to determine the true position of the ship at sea, by the height of the sun, though this latter be enveloped in clouds, or to direct its course by the moon and stars with such exactness and precision, as not to make a mistake of the value of half a degree, or thirty miles; this at least shews the progress and great perfection of an art practised by a class of people, of whose understanding many conceited and supercilious landsmen have but a mean opinion, and whose plain and simple manners they frequently take the liberty of turning into ridicule, forgetting how much they are indebted to their skill and prowess.

"A violent storm of wind will make us tremble with fear, even in a strong well-built house, and in the midst of a populous city; yet we have seldom or never either seen or experienced the vast power of the enraged waves, when beat about by the winds, and dashed against each other till they seem transformed into froth and vapour, and the whole surface of the ocean presents to the eye a confused scene of immense watery mountains and bottomless precipices; and yet on such a sea as this the true seaman, provided he has but a good ship, rides with calm and unshaken courage, and thinks himself as safe in the midst of the ocean as in the best fortified castle."

With gallant pomp and beauteous pride, The floating pile in harbour rode; Proud of her freight, the swelling tide Reluctant left the vessel's side, And rais'd it as it flow'd.

The waves, with eastern breezes curl'd, Had silver'd half the liquid plain; The anchors weigh'd, the sails unfurl'd, Serenely mov'd the wooden world, And stretch'd along the main.

CHAP. XLVI.

CURIOSITIES RESPECTING WATERFALLS, LAKES, GULFS, WHIRLPOOLS, &c.

_The Falls of Niagara--Lake of Killarney--Lake Solfatara--Whirlpool near Suderoe--Maelstrom--Gulf Stream--New Island starting from the Sea._

Fountains and ponds he adds, and lakes immense, Descending streams the winding borders fence; This, deep-absorb'd, the darksome cavern laves, These to the ocean roll their azure waves; There, uncontroll'd, they meet the roaring tide, And dash, for verdant banks, the hoar cliff's side. _Ovid._

NIAGARA is a river of the United States, which flows from Lake Erie, and runs by a north-west course into the south-west end of Lake Ontario, constituting part of the boundary between the United States and Canada. It is thirty-four miles long, including its meanders. About twenty miles below Lake Erie is the great cataract, called THE FALLS OF NIAGARA, which is justly reckoned one of the greatest natural curiosities in the world. These falls run from south-south-east to north-north-west; and the rock of the falls crosses them, not in a right line, but forms a kind of figure like a hollow semicircle, or horse-shoe. Above the falls, in the middle of the river, is an island called Grand Isle, about nine hundred or one thousand feet long, the lower end of which is just at the perpendicular edge of the fall. On both sides of this island runs all the water that comes from the lakes of Canada; viz. Lakes Superior, Michigan, Huron, and Erie. Before the water comes to this island, it runs but slowly, compared with its motion afterwards, when it grows the most rapid in the world, running with a surprising swiftness before it comes to the fall. It is perfectly white, and in many places is thrown high up into the air. At this island, the river divides into two channels: the perpendicular descent of the north-east channel, as measured by Dr. M'Causlin, is one hundred and sixty-three feet; that of the north-west, one hundred and forty-three; and the breadth of the cataract and island, above a mile.

The water that runs down on the west side is more rapid, flows in greater abundance, and is whiter, than that on the east side, and seems to outfly an arrow in swiftness. At the principal fall, on looking up the river, one may see that the water is every where exceedingly steep, almost like the side of a hill; but upon looking at the fall itself, it is impossible to express the amazement it occasions. The height of it, as measured by mathematical instruments, is exactly one hundred and thirty-seven feet; and when the water is come to the bottom, it rebounds back to a very great height in the air. The noise is heard at the distance of forty-five miles. At fort Niagara, when they hear the noise of the fall more loud than ordinary, they are sure that a north-east wind will follow; which is the most surprising, as the fort lies south-west from the fall. Sometimes the fall makes a much greater noise than at others, and this is held for an infallible sign of approaching rain or bad weather. From the place where the water falls, there arises a great quantity of vapour, like very thick smoke, insomuch, that when viewed at a distance, one would think that the Indians had set the forests on fire. These vapours rise high in the air when it is calm, but are dispersed by the wind when it blows hard. In September and October, such quantities of dead water-fowl are found every morning below the fall, on the shore, that the garrison of the fort live chiefly upon them. Besides the fowls, they find several sorts of dead fish, also deer, bears, and other animals, which have tried to cross the water above the fall: the larger animals are generally found broken to pieces. Just below, a little way from the great fall, the water is not rapid, but goes in circles, and whirls like a boiling pot; which however does not hinder the Indians going upon it in small canoes a fishing; but a little further, and lower, the other smaller falls begin.

There is an island in the middle of the river above the fall, where the Indians go often to kill deer, which have tried to cross the river, and are driven upon it by the stream. On the west side of this island are some small islands or rocks of no consequence. The east side of the river is almost perpendicular, the west side more sloping. In former times, a part of the rock, at the fall which is on the west side of the island, hung over in such a manner, that the water which fell perpendicularly from it, left a vacancy below, so that people could go under between the rock and the water; but the prominent part some years ago broke off, and fell down. The breadth of the great fall, as it runs in a semicircle, is reckoned to be about 300 feet. Below the fall, in the holes of the rocks, are great plenty of eels, which the Indians and French catch with their hands. Every day, when the sun shines, may be seen from ten A. M. till two P. M. below the fall, a glorious rainbow, and sometimes two, one within the other. The more vapours that float, the brighter and clearer is the rainbow. When the wind carries the vapours from that place, the rainbow is gone, but appears again as soon as new vapours arise. From the fall to the landing above it, where the canoes from the Lake Erie put ashore, (or from the fall to the upper end of the carrying place,) is half a mile. Lower than this, the canoes dare not venture. They have often found below the fall, fragments of human bodies, that have unhappily been precipitated over the fall. The French say, that they have often thrown great trees into the water above, to see them carried over this precipice with the vast body of water, which nothing can resist: these go down with surprising swiftness, but can never be seen afterwards; from whence has arisen the conjecture that there was a bottomless abyss just under the fall. But the most reasonable supposition is, that, by the powerful agency of the water, they were broken into such diminutive fragments, as to render it impossible that they should ever be recognized for the same. The rock of the fall is composed of a gray limestone.