The counterpart of this current (which in the Atlantic Ocean, between Africa, America, and Europe, belongs almost exclusively to the northern hemisphere) is to be found in the South Pacific, where a current prevails, the effect of whose low temperature on the climate of the adjacent shores I had an opportunity of observing in the autumn of 1802. It brings the cold waters of the high southern latitudes to the coast of Chili, follows the shores of this continent and of Peru, first from south to north, and is then deflected from the Bay of Arica onward from south-southeast to north-northwest. At certain seasons of the year the temperature of this cold oceanic current is, in the tropics, only 60 degrees, while the undisturbed adjacent water exhibits a temperature of 81.5 degrees and 83.7 degrees. On that part of the shore of South America south of Payta, which inclines furthest westward, the current is suddenly deflected in the same direction from the shore, turning so sharply to the west that a ship sailing northward passes suddenly from cold into warm water.
It is not known to what depth cold and warm oceanic currents propagate their motion; but the deflection experienced by the South African current, from the Lagullas Bank, which is fully from 70 to 80 fathoms deep, would seem to imply the existence of a far-extending propagation. Sand banks and shoals lying beyond the line of these currents may, as was first discovered by the admirable Benjamin Franklin, be recognized by the coldness of the water over them. This depression of the temperature appears to me to depend upon the fact that, by the propagation of the motion of the sea, deep waters rise to the margin of the banks and mix with the upper strata. My lamented friend, Sir Humphrey Davy, ascribed this phenomenon (the knowledge of which is often of great practical utility in securing the safety of the navigator) to the descent of the particles of water that had been cooled by nocturnal radiation p 309 and which remain nearer to the surface, owing to the hinderance placed in the way of their greater descent by the intervention of sand-banks. By his observations Franklin may be said to have converted the thermometer into a sounding line. Mists are frequently found to rest over these depths, owing to the condensation of the vapor of the atmosphere by the cooled waters. I have seen such mists in the south of Jamaica, and also in the Pacific, defining with sharpness and clearness the form of the shoals below them, appearing to the eye as the aerial reflection of the bottom of the sea. A still more striking effect of the cooling produced by shoals is manifested in the higher strata of air, in a somewhat analogous manner to that observed in the case of flat coral reefs, or sand islands. In the open sea, far from the land, and when the air is calm, clouds are often observed to rest over the spots where shoals are situated, and their bearing may then be taken by the compass in the same manner as that of a high mountain or isolated peak.
Although the surface of the ocean is less rich in living forms than that of continents, it is not improbable that, on a further investigation of its depths, its interior may be found to possess a greater richness of organic life than any other portion of our planet. Charles Darwin, in the agreeable narrative of his extensive voyages, justly remarks that our forests do not conceal so many animals as the low woody regions of the ocean, where the sea-weed rooted to the bottom of the shoals, and the severed branches of fuci, loosened by the force of the waves and currents, and swimming free, unfold their delicate foliage, upborne by air-cells.*
[footnote] *[See 'Structure and Distribution of Coral Reefs', by Charles
Darwin, London, 1842. Also, 'Narrative of the Surveying Voyage of H.M.S.
"Fly" in the Eastern Archipelago, during the Years ' 1842-1846, by J. B.
Jukes, Naturalist to the expedition, 1847.] — Tr.
The application of the microscope increases, in the most striking manner, our impression of the rich luxuriance of animal life in the ocean, and reveals to the astonished senses a consciousness of the universality of life. In the oceanic depths, far exceeding the height of our loftiest mountain chains, every stratum of water is animated with polygastric sea-worms, Cyclidiae and Ophrydinae. The waters swarm with countless hosts of small luminiferous animalcules, Mammaria (of the order of Acalephae), Crustacea, Peridinea, and circling Nereides, which when attracted to the surface by peculiar meteorological conditions, convert every wave into a foaming band of flashing light.
p 310 The abundance of those marine animalcules, and the animal matter yielded by their rapid decomposition are so vast that the sea water itself becomes a nutrient fluid to many of the larger animals. However much this richness in animated forms, and this multitude of the most various and highly-developed microscopic organisms may agreeably excite the fancy, the imagination is even more seriously, and, I might say, more solemnly moved by the impression of boundlessness and immeasureability, which are presented to the mind by every sea voyage. All who possess an ordinary degree of mental activity, and delight to create to themselves an inner world of thought, must be penetrated with the sublime image of the infinite, when gazing around them on the vast and boundless sea, when involuntarily the glance is attracted to the distant horizon, where air and water blend together, and the stars continually rise and set before the eyes of the mariner. This contemplation of the eternal play of the elements is clouded, like every human joy, by a touch of sadness and of longing.
A peculiar predilection for the sea, and a grateful remenbrance of the impression which it has excited in my mind, when I have seen it in the tropics in the calm of nocturnal rest, or in the fury of the tempest, have alone induced me to speak of the individual enjoyment afforded by its aspect before I entered upon the consideration of the favorable influence which the proximity of the ocean has incontrovertibly exercised on the cultivation of the intellect and character of many nations, by the multiplication of those bands which ought to encircle the whole of humanity, by affording additional means of arriving at a knowledge of the configuration of the earth, and furthering the advancement of astronomy, and of all other mathematical and physical sciences. A portion of this influence was at first limited to the Mediterranean and the shores of southwestern Africa, but from the sixteenth century it has widely spread, extending to nations who live at a distance from the sea, in the interior of continents. Since Columbus was sent to "unchain the ocean"* (as the unknown voice whispered to him in a dream when he lay on a sick-bed near p 311 the River Belem), man has ever boldly ventured onward toward the discovery of unknown regions.
[footnote] *The voice addressed him in these words, "Maravillosamente Dios hizo sonar tu nombre en la tierra; de los atamientos de la mar Oceana, que estaban cerrados con cadenas tan fuertes, te dió las llaves" — "God will cause thy name to be wonderfully resounded through the earth, and give thee the keys of the gates of the ocean, which are closed with strong chains." The dream of Columbus is related in the letter to the Catholic monarchs of July the 7th, 1503. (Humboldt, 'Examen Critique', t. iii., p. 234.)
The second external and general covering of our planet, the aerial ocean, in the lower strata, and on the shoals of which we live, presents six classes of natural phenomena, which manifest the most intimate connection with one another. They are dependent on the chemical composition of the atmosphere, the variations in its transparency, polarization, and color, its density or pressure, its temperature and humidity, and its electricity. The air contains in oxygen the first element of physical animal life, and besides this benefit, it possesses another, which may be said to be of a nearly equally high character, namely, that of conveying sound; a faculty by which it likewise becomes the conveying sound; a faculty by which it likewise becomes the conveyer of speech and the means of communicating thought, and consequently of maintaining social intercourse. If the Earth were deprived of an atmosphere, as we suppose our moon to be, it would present itself to our imagination as a soundless desert.
The relative quantities of the substances composing the strata of air accessible to us have, since the beginning of the nineteenth century, become the object of investigations, in which Gay-Lussac and myself have taken an active part; it is however, only very recently that the admirable labors of Dumas and Boussingault have, by new and more accurate methods, brought the chemical analysis of the atmosphere to a high degree of perfection. According to this analysis, a volume of dry air contains 20.8 of oxygen, and 79.2 of nitrogen, besides from two to five thousandth parts of carbonic acid gas, a still smaller quantity of carbureted hydrogen gas,* and, according to the important experiments of Saussure and Liebig, traces of ammoniacal vapors,** from which plants derive their nitrogenous contents.