The Sea and Its Living Wonders / A Popular Account of the Marvels of the Deep and of the Progress of Martime Discovery from the Earliest Ages to the Present Time

by G. Hartwig

Perpetual motion and change is the grand law, to which the whole of the created universe is subject, and immutable stability is nowhere to be found, but in the Eternal mind that rules and governs all things. The stars, which were supposed to be fixed to the canopy of heaven, are restless wanderers through the illimitable regions of space. The hardest rocks melt away under the corroding influence of time, for the elements never cease gnawing at their surface, and dislocating the atoms of which they are composed. Our body appears to us unchanged since yesterday, and yet how many of the particles which formed its substance, have within these few short hours, been cast off and replaced by others. We fancy ourselves at rest, and yet a torrent of blood, propelled by an indefatigable heart, is constantly flowing through all our arteries and veins.

A similar external appearance of tranquillity might deceive the superficial observer, when sailing over the vast expanse of ocean, at a time when the winds are asleep, and its surface is unruffled by a wave. But how great would be his error! For every atom of the boundless sea is constantly moving and changing its place; from the depth to the surface, or from the surface to the depth; from the frozen pole to the burning equator, or from the torrid zone to the arctic ocean; now rising in the air in the form of invisible vapours, and then again descending upon our fields in fertilising showers.

The waters are, in fact, the greatest travellers on earth; they know all the secrets of the submarine world; climb the peaks of inaccessible mountains, shame the flight of the condor as he towers over the summit of the Andes, and penetrate deeper into the bowels of the earth than the miner has ever sunk his shaft.

Leaving their wanderings through the regions of air to the next chapter, I shall now describe the principal ocean currents, the simple, but powerful agencies by which they are set in motion, their importance in the economy of nature, and their influence on the climate of different countries.

Even in the torrid zone, the waters of the ocean, like a false friend, are warm merely on the surface, and of an almost icy coldness at a considerable depth. This low temperature cannot be owing to any refrigerating influence at the bottom of the sea, as the internal warmth of the earth increases in proportion to its depth, and the waters of profound lakes, in a southern climate, never show the same degree of cold as those of the vast ocean.

The phenomenon can thus only arise from a constant submarine current of cold water from the poles to the line, and strange as it may seem, its primary cause is to be sought for in the warming rays of the sun, which, as we all know, distributes heat in a very unequal manner over the surface of the globe.

Heat expands all liquid bodies, and renders them lighter; cold increases their weight by condensation. In consequence of this physical law, the waters of the tropical seas, rendered buoyant by the heat of a vertical sun, must necessarily rise and spread over the surface of the ocean to the north and south, whilst colder and heavier streams from the higher latitudes flow towards the equator along the bottom of the ocean, to replace them as they ascend.

In this manner, the unequal action of the sun calls forth a general and constant movement of the waters from the poles to the equator, and from the equator to the poles; and this perpetual migration is one of the chief causes by which their purity is maintained. These opposite currents would necessarily flow direct to the north or south, were they not deflected from their course by the rotation of the earth, which gradually gives them a westerly or easterly direction.

The unequal influence of the sun in different parts of the globe, and the rotation of the earth, are, however, not the only causes by which the course of ocean-currents is determined.

Violent storms move the waters to a considerable depth, and retard the flow of rivers, and thus it is to be expected that continuous winds, even of moderate strength, must have a tendency to impel the waters in the same direction.