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ART. II.-ATMOSPHERIC AND OCEANIC CURRENTS.
Currents and Changes of the Atmosphere and the Sea. By M.
FELIX JULIEN, Lieutenant in the Navy, and formerly a Pupil of the Polytechnic School. One volume, 8vo. Paris : Lacroix &
Baudry. 1860. WHERE do the fragile nautili go? What directing hand guides them from one sea to the other? What breeze fills the violetcolored sails of their frail shell, that plows the waves of the sea, and braves their fury? What mysterious compass directs the flotilla of these slight and graceful Argonauts, which sail in consort toward Cape Horn, and arriving there separate, the one part for the Pacific, the other for the Atlantic Ocean. Too soon, alas ! the ephemeral life that animates these tiny navigators will be extinct, and the light shell, borne to distant seas by force of lower currents, like the leaf carried through the air by the wind, will descend from depth to depth by an insensible fall, even to the bottom of the deep. Some day science will sound the depth to which it has fallen, and this little shell will give the solution of a problem for a long time unsolved, in revealing the existence of the submarine currents that have carried it so far from its natal sea. For as the atmospheric ocean, so the ocean of waters, has its two kinds of currents — surface and submarine. They are both, as yet, but imperfectly understood. The first was noticed early. Captain Duperry, of the French Institute, was the first to make a chart, which Lieutenant Maury has since perfected.
The existence of submarine currents was suspected twentyfive years ago by the penetrating genius of Arago, and has since been established without doubt by scientific reasoning, and above all by the observation of certain facts, the most important and striking of which we will state. Does not the identity of the constituent principles of water from all latitudes prove that invisible currents are charged with the task of continually re-establishing its equilibrium ?
As in the case of the winds, solar heat is the principal agent recognized in the formation of oceanic currents, and the intertropical zone is still the grand laboratory. When the vertical sun of the torrid regions heats the water, a double phenomenon is produced : first, the surface water is evaporated and the oceanic mass is diminished ; secondly, the salts, disengaged by the evaporated water, owing to their specific gravity, are precipitated to the bottom, and carry with them the water that they saturate and make heavier; consequently two currents are formed—the one a surface current, bringing from the north and the south the colder and lighter waters, to supply the place of that which was evaporated; the second submarine, which carries to the north and south the heavy equatorial waters until they are equal in weight and saltness with the surrounding waters.*
It is thus that science has solved the problem of the utility of the salts of the sea, so long unexplained, by recognizing in them the most powerful agents in promoting the currents. This is not all; by a recent and curious experiment Professor Champman has proved that evaporation is greater in fresh than in salt water; the difference is about half per cent., (0.54.) The salts of the sea are not then only necessary in the formation of currents; they have also been destined by Providence to interpose as a protecting screen between the sun and the ocean, in order to modify the evaporating power of the former, and to prevent such an abundant precipitation as to deluge the earth with rains.
What is the origin of the saltness of the sea? Opinion is divided: one party believing that the water-courses wash out the salts from the land and convey them to the ocean ; the other, and Maury with them, relying on geological facts, believe that the sea has always been salty. Maury thinks that if the salts of the sea were separated from the water that contains them, and collected together, they would form a gigantic cube of seventy-six yards in height, whose base would be equal to the superficies of North America. Could such a colossal mass be taken with impunity from the solid earth by the watercourses? Would not its displacement disturb the center of gravity of our planet ? Maury thinks it would. All the seas are not equally salty. The Mediterranean, for
* Lieut. Maury: Physical Geography of the Sea.
example, is less so than the ocean. The Black and Baltic are half as much as the Mediterranean. Lake Baikal, formerly salty, as proved by the seals, sponges, and other marine animals which live in these waters, has ceased to be so. The saltness of water differs according to the evaporation and precipitation.
What then becomes of the calcareous matters, and the salts that rivers and streams carry unceasingly into the ocean? Here again wonders press upon us so that we do not know which to admire the most.
Who has sent forth the innumerable army of microscopic architects, that by means of the powerful organism with which they are provided assimilate the salts held in suspension by the sea water, and, using them for materials, construct the wonderful palaces of coral, and raise future continents by degrees from the depths of the ocean ?*
Each drop of water furnishes its contingent of material, and becomes, in its turn, the workshop in which these gigantic constructions are formed. While the solid particles which it contains have been extracted and transformed by some one of these invisible world-builders, the liquid molecule being lightened, mounts to the surface and is replaced by a heavier drop, which, in its turn, carries new material to the indefatigable workman. If we consider that the number of imperceptible workmen is incalculable, as well as the drops of water thus incessantly displaced, we must recognize here one cause of the disturbance of the waters of the ocean, an insignificant one if we regard the effect produced by each one of these animalcules, but relatively powerful if we regard the work of the entire species.
Such is the wonderful profusion of existences with which the lavish liberality of the Creator has peopled the seas, that Alexander Humbolt has said that the waters are entirely composed of living beings. In the glacial seas, where life would seem to be extinct, there is an extent of from twenty to thirty thousand square miles, where the animalcules are so abundant that Scoresby estimates that it would take not less than 5,000 years for 20,000 persons to count the number contained in two thousand five hundred yards. How does it happen that a vessel sometimes for many days traverses a brilliant sea, and that at night the waves from the keel glitter with the shining light? These shining waves, this milk-white sea is nothing but a mass of phosphorescent animalcules, that the submarine disturbances have caused to mount from the lower strata, where they live, and offer themselves as prey for the whales. *
* To mention only one instance of such facts—the Strait of Torres witnesses the ceaseless increase of these madipore islands; in two hundred and fifty years the number has increased from twenty-six to one hundred and fifty, and the day is not far distant when the army of zoophytes will succeed in stopping up its passage.
By means of the ingenious apparatus recently invented by the aspiring American, Brooke,t we can sound the depths of the ocean.
A chart of the depth of most of the northern Atlantic has been made by Maury. Of the valleys which it covers, the deepest have been found to the south of the Banks of Newfoundland. They are not less than four thousand fathoms deep. The substances brought up from the bottom of the sea by Brooke's sounding apparatus all belong to the animal kingdom; these are the foraminiferous shells, of which the microscope reveals the spotless purity, the well-defined outlines, and the delicate chiseling in all their original freshness—a new and brilliant proof that at the bottom of the zones which are agitated by the currents and the storms there exists in the ocean a region of absolute calm, of eternal repose, the mysterious regions of the blue waters. This offers to us a new occasion to proclaim the marvelous wisdom of Him who created and arranged the world. This bed of water, the constant repose of which the most frightful storms never disturb, what is it, in truth, but a barrier interposed between the motion of the higher strata of water and the solid crust of the globe, in order to prevent the submarine currents from washing and destroying the latter? As the summits of mountains, so the bottom of the ocean is free from storms. And again, as the mountains, so the depths of the waters are covered with an eternal snow; a shower of white shells—the remains of life as ephemeral as innumerable-falls there without cessation from the superincumbent waters in which they have lived, and every day adds to the shining mantle, from which Brooke's sounding apparatus brings us specimens, and with which the depths seem everywhere to be covered.*
* Let us remark here that animal life does not exist at all depths of the sea; as we leave the surface the variety of kinds and the numbers decrease. Mr. Ed. Forbes has counted eight zones of life in a depth of two hundred and thirty fathoms. The extreme point of animal life in the Mediterranean does not reach a greater depth than three hundred fathoms.
Since the invention of Brooke's sounding apparatus, Russell has discovered the means of computing the depth of any sea, on the principle that the deeper the water the more rapid the waves. The calculations of this savant have resulted in assigning a medium depth of about thirty fathoms to the British Channel, two thousand four hundred to the Atlantic, and three thousand two hundred to the Pacific. In the deep seas the tide advances at the rate of about three hundred and sixty miles per hour.
It is thus that the microscopic inhabitants of the ocean affect the great meteorological law: While the currents carry the materials of their edifices to the bottom of the ocean, they contribute on their part to maintain constantly the equilibrium of the water, whether in creating the circulation or in purifying them of the various salts that they contain."
We will pursue the study of the currents. The Atlantic, whose length is such that it stretches from one pole to the other, and whose breadth is comparatively narrow, receives by the streams and the rains much more water than it loses by evaporation. Nearly all the streams of the Old and New World are tributary to it. The Mississippi, the St. Lawrence, the Rio de la Plata, and the Amazon are of themselves more than sufficient to supply the evaporation. And when we think that, in addition to the rain and water-courses, the two great polar currents, Arctic and Antartic, are continually pouring their enormous quantities of water into the bosom of this
* Ehrenberg, in analyzing with the microscope a cubic inch of the rotten-stone of Bilia, discovered in it an entire fossil world, composed of the callapash of infusoria, which he estimated at the prodigious number of forty thousand millions ! that is to say, in an infinitesimal world having an inch of extent, prodigal nature had inclos. ed a number of beings greater than that of men and large animals upon the surface of the earth. What then must be the miraculous multitude of these animalcules if we suppose the bottom of the ocean to be carpeted with their debris, and that the continents are for the most part formed of them. And yet the infusoria are far from occupying the last degree in the scale of being. Herschell once examined a drop of water with his solar microscope, and in this molecule, which, enlarged by the wonderful instrument, had acquired a size of about twelve feet in diameter, the celebrated astronomer discovered with astonishment such a quantity of animalcules of all forms and every species, that in the space of twelve feet it was impossible to place the point of a needle upon any unoccupied spot! Man's reason becomes bewildered under the effect of such wonders.