TIDES AND CURRENTS.
Alternate tides in sacred order run.—Blackmore.
Among the most wonderful phenomena of nature may be reckoned the tides of the sea. They were but little understood by the ancients, although Pliny, Ptolemy and Macrobius, were of opinion that they were influenced by the sun and moon. The former expressly says, that the cause of the ebb and flow is in the sun, which attracts the waters of the ocean; and he adds, that the waters rise in proportion to the proximity of the moon to the earth.
The phenomena of the tides have been ascribed to the principle of innate gravitation; but Sir Richard Phillips, in his theory of the system of the universe, refers them to that general law of motion which he considers as the primary and proximate cause of all phenomena, operating, in a descending series, from the rotation of the sun round the fulcrum of the solar system, to the fall of an apple to the earth. This motion being transferred through all nature from its source, serves as the efficient cause of every species of vitality, of every organic arrangement, and of all those accidents of body heretofore ascribed to attraction.
The waters of the ocean are observed to flow and rise twice a day, in which motion, or flux, which in the same direction lasts nearly six hours, the sea gradually swells, and, entering the mouths of rivers, drives back the river-waters toward their head. After a continued flux of six hours, it seems to repose for a quarter of an hour, and then begins to ebb, or retire back, for six hours more; in which time, by the subsidence of the waters, the rivers resume their usual course. After a quarter of an hour, the sea again flows and rises as before.
According to the theory of Newton, these phenomena were supposed to be produced by an imaginary power called attraction. The moon was supposed to attract the waters by the influence of an occult power inherent in all matter; just as the earth was supposed to attract the moon, the moon the earth, and the planets one another. Others, again, ridicule this idea, as unsustained and visionary, giving in their turn some theory that has no better argument to sustain it. And it is probable the time is yet future when we shall have any theory that will fully account for all the phenomena of the tides. On account of the shallowness of some seas, and the narrowness of the straits in others, there arises a great diversity in the phenomena, only to be accounted for by an exact knowledge of the place. For instance, in the English channel and the German ocean, the tide is found to flow strongest in those places that are narrowest, the same quantity of water being, in this case, driven through a smaller passage. It is often seen, therefore, rushing through a strait with great force, and considerably raised, by its rapidity, above that part of the ocean through which it runs.
The shallowness and narrowness of many parts of the sea, give rise also to a peculiarity in the tides of some parts of the world: for in many places, in the British seas in particular, the greatest swell of the tide is not while the moon is in its meridian hight, and directly over the place, but some time after it has declined thence. The sea, in this case, being obstructed, pursues the moon with what dispatch it can, but does not arrive with all its waters, until after the moon has ceased to operate. Lastly, from this shallowness of the sea, and from its being obstructed by shoals and straits, it happens that the Mediterranean, the Baltic and the Black sea, have not any sensible tides, to raise or depress them in a considerable degree.
Among the phenomena of the tides, one of the most singular is the bore, peculiar to several rivers: it is ascribed to the waters, which were before expansive, being suddenly pent up, and confined within a narrow space. This bore or impetuous rush of waters, accompanies the first flowing of the tide in the Ferret, in Somersetshire, and in the Seine, in France. It is also one of the peculiarities of the Severn, the most rapid river in England.
One of the greatest known tides is that of the Bristol channel, which sometimes flows upward of forty feet. At the mouth of the river Indus, the water rises thirty feet. The tides also are remarkably high on the coasts of Malay, in the straits of Sunda, in the Red sea, at the mouth of the river St. Lawrence, along the coasts of China and Japan, at Panama, and in the gulf of Bengal. The most remarkable tides, however, are those at Batsha, in the kingdom of Tonquin, in twenty degrees, fifty minutes, north latitude. In that port, the sea ebbs and flows once only in twenty-four hours, while in all other places there are two tides within that space. What is still more extraordinary, twice in each month, when the moon is near the equinoctial, there is not any tide, the water being for some time quite stagnant. These, with other anomalies of the tides there, Sir Isaac Newton, with peculiar sagacity, ascertained to arise from the concurrence of two tides, one from the South sea, and the other from the Indian ocean. Of each of these two tides there come successively two every day; two at one time greater, and two at another which are less. The time between the arrival of the two greater was considered by him as high tide; that between the two less, as ebb. In short, with these simple facts in his possession, that great mathematician solved every appearance, and so established his theory as to silence every opposer.
Besides the common and periodical tides, a variety of local currents are met with in different seas, on different parts of the ocean, and for the greater part at an inconsiderable distance from land. They have been usually ascribed to particular winds; but their origin is not easy to trace, as they have been occasionally found beneath the surface of the water, running in a contrary direction to the stratum above, and can not, therefore, have been owing to winds or monsoons. These particular currents have been ascribed to the immense masses of polar ice, which produce a greater degree of cold in the under than in the upper stratum of waters; and it has been suspected that there is an under-current of cold water flowing perpetually from the poles toward the equator, even where the water above flows toward the poles. The great disparity of temperature which is frequently found in deep and superficial soundings of the same space of water, is thus accounted for.
The most extraordinary current of this kind, is that of the gulf of Florida, usually called the Gulf stream, which sets along the coast of North America to the northward and eastward, and flows with an uninterrupted rapidity. It is ascribed to the trade-winds, which, blowing from the eastern quarter into the great Mexican gulf, cause there an accumulation above the common level of the sea. The water, therefore, constantly runs out by the channel where it finds least resistance, that is, through the gulf of Florida, with such force as to continue a distinct stream to a very great distance. A proof of its having thus originated is, that the water in the Gulf stream has been found to have retained a great portion of the heat it had acquired in the torrid zone.
A very singular upper current often prevails to the westward of Scilly, and is highly dangerous to ships which approach the British channel. Currents of this description are, however more frequently met with about the straits of Gibraltar, and near the West India islands, the coasts of which are so subject to counter-tides, or extraordinary currents, that it is often dangerous for boats to land. They proceed to the westward, along the coasts of Yucatan and Mexico, and running round into the gulf, return into the great ocean by the straits of Bahama, along the coasts of Florida, in order to pursue, in the north, the course ordained them by the great Author of nature. In this course the waters run with an extraordinary rapidity, passing on, however, by a motion so even and imperceptible, that their speed is not realized by the spectator. But against the shores and coasts of the various islands in their way, their progress becomes very manifest, and even dangerous, interrupting the navigation, and rendering it hardly possible to stem them in their course.
In addition to these regular currents, there are others, called counter-tides, which are observable on the sea-coasts and shores. In places where these flow, the sea rolls and dashes in an extraordinary manner, becoming furious without any apparent cause, and without being moved by any wind. The waves rise and open very high, breaking on the shore with such violence, that it is impossible for vessels to land. These counter-tides have been, by some, ascribed to the pressure of the heavy black wind-clouds which are occasionally seen to hang over an island, or over the sea where they occur, though it is far more probable that in every case they are caused by under-currents and hidden shoals, by which the ordinary currents are checked and broken so as to cause the effects described.
Somewhat similar to these, at least in its hidden cause, is the celebrated Maelstrom on the coast of Norway, a view of which is given in the cut. This is caused by the tides, in their violent passage between the Loffoden islands; and its terrors, though at all times great, are sometimes greatly increased by the winds. The roar of the sea, when the Maelstrom is in full action, is said to be terrific. It is stated that not only ships, but even whales, have been sucked into this vortex, and killed by being dashed against the hidden rocks. The following description, though imaginary, gives a correct idea of the destruction of a ship in this whirlpool.
THE MAELSTROM.
“The breeze, which had been long flagging, now lulled into a calm, and soon a low continual hum, like that of an army of bees, which seemed to rise out of the stilled ocean, became audible to every ear. Not a word was spoken; every one held his breath whilst he listened with an intensity of eagerness that betokened the awe that was fast filling the heart. ‘It is the Moskoestrom!’ cried the boatswain. ‘The Moskoestrom!’ echoed the crew. ‘Away, men!’ shouted the mate; ‘down to the hold, bring up the spare sails, clear the deck, set up a spar for a mast; away, away!’
“The din of preparation drowned the stern hum of the distant whirlpool: there was, however, an anxious pause when the new sail was set into the air; and experienced sailors suffered themselves to be cheated with the hope that there was still breeze enough to make the good ship answer her helm. But, alas! the heavy canvas refused to expand its folds, and not a breath of wind ruffled the dull surface of the sullen waters. They had not another hope; the sailors looked on one another with blank dismay, and now they heard, with awful distinctness, the roar of the terrible Maelstrom, and the frowning rocks of Loffoden were but too plainly visible on the right. It became evident to all, that the ship, borne along by the tide, was fast drawing near the dreadful whirlpool. The vessel continued slowly to approach, and the certainty of unavoidable death became every moment more overpowering and intense. At first the sailors stood together in a group, gazing gloomily upon one another; but as the roar of the whirlpool became louder and louder, and the conviction of inevitable destruction became stronger, they all dispersed to various parts of the ship. * * *
“It was a beautiful day; the sun shone forth without a cloud to dim his luster, the waves sparkled beneath his influence, and the white plumage of a thousand busy sea-birds became more dazzling with his rays. The isle of Moskoe was close at hand, and looked cheerful and inviting, but the ship was not to approach nearer to its shores; the stream which bore her along never suffered any vessel to pause in its career. And now there arose at some distance ahead of the vessel, a horrible and dismal bellowing. It was the voice of the leviathan in his agony; and when those on deck who had still ears for exterior sounds looked forward to ascertain its cause, they beheld a huge black monster upon the surface of the sea, struggling against the irresistible stream, and with his immense tail lashing the waters into foam, as he vainly strove to escape from destruction. They beheld him borne away by the might of his furious enemy; and they heard his last roar above the noise of the whirlpool, as he was sucked down into the never satisfied abyss, and disappeared from their eyes to be torn to atoms; for such is the fate of everything that seeks the depths of the Maelstrom.
“The ship glides along faster and faster; she begins to toss and roll uneasily in the angry rapids that boil around her; her race is nearly run. Terrible! terrible moment! The ship hurries on to her doom with mad impetuosity. She is in the rapids! she hurries along swift as a flash of fire. She is in the whirl of water! round, round, round she goes; her inmates catch hold of her bulwarks and of each other, to steady themselves. And now her bow sprit is under the waves, and a wild shriek of despair rises into the sky! The whirlpool, with greedy jaws, has sucked her under.”
The water of the whirlpool is said to be two hundred and fifty feet deep, and at ebb its noise is as loud as a cataract. In 1645, it was so violently agitated by a storm, that in Moskoe the houses were so shaken as to cause the stones to fall to the ground. Fragments of vessels wrecked in the Maelstrom are frequently seen on the coast, brought up by the return of the tide, their edges mashed and jagged as with a saw, which would induce the belief that the bottom is composed of sharp rocks.
Similar in its cause to the Maelstrom, though on a much inferior scale, is the current, or whirlpool, called Hurlgate or Hellgate, between the East river and Long Island sound, near New York. In the narrow channel here, the tide flows backward and forward with great force; and there being large, irregular rocks in this channel, the water is thrown into the most violent agitation. In passing through the place, it is easy to see the waves seeming to boil as if in a pot. This place is dangerous to vessels, and many have been wrecked here; though the navigation is now so well understood, that fewer accidents happen than formerly. The steamboats generally pass in safety, but still the superb Oregon got upon the rocks here, within a few years, and came near being lost.
Between Sicily and the main land are the straits of Messina, where the current is rapid. Ancient mariners deemed this a terrible place; one side they called Scylla, and the other Charybdis. The poets depicted the sailor in this rapid, as beset by horrors; for if he escaped Scylla on one side, Charybdis was ready to dash him in pieces on the other. This idea has come down to our day, and has even passed into a proverb.