A Book of the United States. VariousЧитать онлайн книгу.
these sands, and the land is gaining on the sea. No vessels, says Humboldt, drawing more than twelve and a half inches water, can pass over these sand-bars without danger of grounding.
The Mississippi is the principal tributary of the Gulf of Mexico, and carries down with it, besides its vast body of waters, a prodigious quantity of organic and unorganic debris. The town of New Orleans, near the mouth of this river, is the principal commercial station along the whole gulf. In the middle of the gulf the winds blow regularly from the north-east; but they vary considerably on approaching the shore. From the Mississippi, along the Florida coast, the south-west wind blows violently in the months of August, September, and October; the north wind prevails during the other nine months. Between the Mississippi and San Bernardo, the wind generally blows in the morning from the south-east or east-south-east, and in the evening from the south-west. Between Catoche and Campeachy the reigning wind, during a great part of the year, blows from the north-east; but from the end of April to September, it comes from the opposite direction. The most remarkable current in the gulf, is that called the Gulf Stream, described in the following chapter.
GENERAL REMARKS ON BAYS.
Many portions of the land and sea extend reciprocally the one into the other. If the sea penetrate into the interior of any continent, it forms there a mediterranean, or inland sea, almost surrounded by land, and having only a narrow opening into the sea. If the extent of such seas be less, and the opening larger, they are called gulfs or bays, two terms which geographical writers have wished to distinguish, but which customary language more frequently confounds. The still smaller portions of sea, surrounded as it were by land, and which afford a shelter for ships, are called ports, creeks, or roads. The first term means a secure asylum; the second is applied to places or ports of much smaller size, and which, when improved or completed by artificial aid, are styled harbors, and roads afford only a temporary anchorage and security from certain winds. The principal bays in the world are Baffin’s, Hudson’s, James’s, Fundy, Massachusetts, Narraganset, Delaware, Chesapeak, Campeachy, Honduras, Bristol, All Saints, Cardigan, Donegal, Galway, Biscay, Bengal, Walwich, Table, False, Angola, Natal, Saldanha, and Botany. The principal gulfs are St. Lawrence, Mexico, Amatique, California, Panama, Guayaquil, St. George, Bothnia, Finland, Riga, Genoa, Naples, Taranto, Venice, Salonica, Persian, Ormus, Siam, Tonquin, Corea, Obi, and Guinea. The principal sounds are Long Island, Albemarle, Pamlico, Prince William’s, Queen Charlotte’s and Nootka.
CHAPTER XII.—OCEANS.
THE United States are washed by the Atlantic Ocean on nearly the whole of their eastern coast, and by the Pacific on a large portion of their western boundary.
Under the name of the Atlantic, is comprised that mass of water between the eastern coast of America and the western coast of Europe and Africa. In its narrowest part, between Europe and Greenland, it is one thousand miles wide, and opening thence to the south-west with the general range of the bounding continents, spreads under the northern tropic to a breadth of sixty degrees of longitude, or four thousand one hundred and seventy miles, without estimating the Gulf of Mexico. The general phenomena on the two opposing sides of the Atlantic have great resemblance. The Atlantic coast of the United States presents an elliptic curve in its entire extent, with three intermediate and similar curves; the first extending seven hundred miles from Cape Florida to Cape Hatteras, the second from Cape Hatteras five hundred miles to the outer capes of Massachusetts, and the third formed by the coasts of Massachusetts, New Hampshire and Maine. Opposite to the United States, the Atlantic admits soundings in every place near the shores, always deepening very gradually. We have not found an exact comparison of the natural history of the Atlantic with that of other oceans. The chief phenomenon that marks it along the coast of the states is the Gulf Stream.
Besides the regular periodical currents produced in the ocean by the tides, various others arise from different causes.31 The waters of the sea may be put in motion by an external impulse, by a difference in temperature and saltness, by the periodical meeting of the polar ice, or by the inequality of evaporation that takes place in different latitudes. Sometimes several of these causes concur in producing the same effect; at others, their actions are opposed to one another, and their effects wholly or partially destroyed. Some of those currents constantly follow the same direction, others are subject to periodical changes, whilst a third class are more accidental. The most regular and extensive current on the globe is that which constantly flows from east to west, between the tropics, and extends on each side of the equator to about the thirtieth degree of latitude.
This vast current necessarily results from the attraction of the heavenly bodies, the diurnal motion of the earth, and the direction of the trade winds. Its existence is incontestibly proved by the fact, that vessels sailing to the westward, are always ahead of their reckoning; that is, their real situation, as determined by observations of the heavenly bodies, is always found to be west of that estimated from the rate of which the vessel is supposed to sail, as impelled by the wind alone. This difference of situation is occasioned by the general movement of the waters in the same direction, and is, consequently, the proper measure of the current. This is the reason why navigators, in sailing from Europe to America and the West India Islands, make the latitude of the Canaries, and then shape their course in the direction of the wind and current across the Atlantic.
A general current also flows from the poles towards the equator. This arises from the increased evaporation in the equatorial regions, and the augmented temperature of the waters, which render them specifically lighter than those of the ocean in higher latitudes, as well as from the increased supplies produced by the melting of the polar ice; all of which render these currents necessary to maintain the equilibrium of this perpetually circulating fluid. Their existence and effects are fully attested by the enormous masses of polar ice, which they convey into the more temperate regions of the ocean, and which sometimes float as low as forty degrees of latitude.
These general currents are greatly modified, and changed into various directions by the obstacles they encounter in their progress. The coast of America, and the numerous islands with which it is flanked, intercept the general current of the Atlantic, and create what navigators call the Gulf Stream. This great current enters the Gulf of Mexico, and, sweeping round the shores of that gulf, issues with accelerated velocity towards the north, by the channel between the southern point of Florida and the Bahama Islands.32 It then rolls along the shore of North America, diminishing in velocity, but increasing in breadth, till it reaches the great bank of Newfoundland. There it suddenly turns towards the east and south-east, and flows with still decreasing velocity, towards the shores of Europe, the Azores, and the coasts of Africa. Navigators readily distinguish this current by the high temperature of its waters, their great saltness, their indigo color, and the shoals of sea-weed33 that cover their surface.
Humboldt, in May, 1804, observed its velocity in the twenty-seventh degree of latitude, and found it about eighty miles in twenty-four hours, though the north wind blew very strongly at the time of the observation. When it issues from the Gulf of Florida, its velocity resembles that of a torrent, and is sometimes five miles an hour, but at others not more than three. Between the nearest point of Florida, and the bank of Bahama, the breadth is only fifteen leagues, but a few degrees further north, it is seventeen; in the parallel of Charleston it is from forty to fifty leagues in breadth, and in latitude forty degrees and twenty-five minutes, this is increased to nearly eighty leagues. The waters of the torrid zone, being thus forcibly impelled towards the north-east, preserve their high temperature to such a degree, that, in latitude forty and forty-one degrees, it has been found to be seventy-two degrees of Fahrenheit, while out of the current the temperature of the water was only sixty-three degrees.
In the parallel of New York the temperature of the Gulf Stream is equal to that of the sea in latitude eighteen degrees. When the current reaches the western islands of the Azores, where the breadth is about one hundred and sixty leagues, the waters still preserve a part of the impulsion they receive in the Gulf of Florida, nearly one thousand leagues distant. Hence the current proceeds to the Canaries and the coast of Africa, and in the latitude of Cape Blanco, where the waters flow