CHAP. XLIV.
CURIOSITIES RESPECTING THE SEA.
General Observations respecting the Sea, or Ocean—Particular Curiosities of the Sea—On the Saltness of the Sea—On the Tides—Waves stilled by Oil.
| “———————And thou, majestic main, A secret world of wonders in thyself! Sound His stupendous praise, whose greater voice Or bids you roar, or bids your roaring fall!” |
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.