OUR KNOWLEDGE OF THE EARTH AND SEA—HOW IT HAS INCREASED—THE EARTH THE DAUGHTER OF THE OCEAN—THE OPINION OF SCIENCE—THE MEAN DEPTH OF THE OCEAN—THE EXTENT OF THE OCEAN—ITS VOLUME—SPECIFIC GRAVITY OF SEA-WATER—CONSTITUTION OF SALT-WATER—THE SILVER IN THE SEA—THE WAVES OF THE SEA—THE CURRENTS OF THE OCEAN—THE TIDES—THE AQUARIUM—THE COMMERCE OF MODERN TIMES—THE SPREAD OF PEACE.

In the preceding pages the facts have been given in a comprehensive though succinct form, which enable us to see how, step by step, each one of which became possible only when those preceding had been taken. Mankind has gained a knowledge of the outlines of the sea; of the form of the earth itself; of the relative positions occupied by the water and the land; of their action upon each other, and thus the way has been prepared by the enterprise of preceding generations for the scientific methods of study which characterize the modern era. The adventurous voyagers of the early times, who, daring as they were, hardly were bold enough to venture in their open boats, propelled only by oars, out of the sight of land, could not be expected to conceive that it could be possible for men, like themselves, to ever become able to construct ships such as modern nations construct, in which, propelled by steam, voyages should be taken across oceans, and out of sight of land, their course over the trackless waters be guided with accuracy and certainty, to any desired point, by the compass and the observations of the motions of the stars.

By experiment and observation the entire aspect and conception of the ocean has been changed in modern times from that which prevailed in antiquity, or even more recently, until within the few past generations. Though much has been done, in the study of the ocean, toward obtaining a proper conception of its influence in the general economy of the globe, yet there is still much to be learned. Among the ancients it was generally declared in their cosmogonies that the solid portions of the world were produced by the ocean. "Water is the chief of all," says Pindar; "the earth is the daughter of ocean," is the mythological statement common to the primitive nations. Though this poetical expression was merely based upon a vague tradition, and can hardly be taken as the result of any methodical study of the earth, yet modern science tends to show that it is really true. The ocean has produced the solid land. The study of geology, the skilled inspection of the various strata of the land—the rocks, sand, clay, chalk, conglomerates—proves that the materials of the continents have been chiefly deposited at the bottom of the sea, and raised to their present position by the chemical or mechanical agencies which are constantly at work in the vast laboratory of nature.

Many rocks, as for instance the granites of Scandinavia, which were previously believed to have been projected in a molten and plastic state from the interior of the earth, where they had been subjected to the action of the intense heat supposed to exist in the centre of the earth, are now supposed to be in reality ancient sedimentary strata, slowly deposited by the sea, and upheaved by the contraction of the crust, or by some other force of upheaval acting from the centre. Upon the sides of mountains, or on their summits, now thousands of feet above the level of the ocean, unquestionable traces of the action of the sea can be found. And the scientific observer of to-day sees all about him evidences that the immense work of the creation of continents, commenced by the sea in the earliest periods of time, is to-day continuing without relaxation or intermission, and with such energy that even during the short course of a single life great changes can be seen to have been produced. Here and there a coast, subject to the beating of the serf, is seen to be slowly undermined, disintegrated, worn down and carried away, while in another place the material is deposited by the sea, and sandy beaches or promontories are built up. New rocks also, differing in appearance and constitution from those worn away, are formed. But beside this action of the sea upon the coasts, in constantly changing the configuration of the land, modern observation has shown us that animal life is an agent constantly at work within the sea itself, in the formation of new lands. The innumerable minute forms of life with which the sea swarms; the coral polyps, the shells, the sponges, and the animalculÆ of all kinds, are constantly engaged in consuming the food they find, in reproducing themselves, and in dying. From the various matters brought down to the ocean by the rivers of the land, they secrete their shells or other coverings; and as generation after generation they die, these falling to the bottom form immense banks, or plains, which some future action of upheaval will bring above the surface to form the material for new continents or islands.

Thus while the ocean prepares the materials for the future continents in its bosom, it also furnishes the waters which wash away the lands already existing. To the thought of modern science the granite peaks, the snow-clad mountains, immovable and eternal as they seem, are constantly disintegrating, and partake, with every thing else in creation, the eternal round of change which is constantly going on. From the sea, by evaporation, rise the vapors which, condensing against the sides of the mountains, form the glaciers; and these, slowly sliding down toward the plains, are such efficient agents in wearing away the mountains, grinding up their solid rocks and preparing the gravel which the mountain streams distribute over the plains. From the sea the atmosphere receives the moisture destined to return in rain from the clouds; to feed the brooks whose union forms the rivers, destined again to return to the sea the waters it provided, and thus keep up, in a single, mighty and endless circulation, the waters of the globe.

Thus to the agency of the ocean we are indebted for our rivers, which have played such an important part in the geological history of the earth, in the distribution of the flora and fauna of various countries, and on the life of man himself. In the study also of the climates of the earth, and their effects upon life, we find the ocean bears a most important part. As the circulation of the atmosphere mingles the heated air from the equator with that of the frozen regions of the poles, so the currents of the ocean circulate about the earth, blending the contrasts of climate, and making a harmonious whole of all the different portions. Thus, instead of considering the ocean as the barren waste of desolation it appeared to the ancients, to the modern thinker the ocean has, layer by layer, deposited the land from its bosom, and now by its vapors provides the rains which support its vegetable life, upon which all other life depends, and creates the rivers and the springs, which play such an important part in the modification of the interior of continents, at the greatest distance from the sea.

The mean depth of the whole mass of the ocean waters of the globe is estimated at about three miles, since measurements have shown that the basins of the Atlantic and Northern Pacific are deeper than this by hundreds of thousands of fathoms. The extent covered by the surface of the ocean has been estimated at more than 145,000,000 of square miles, and with this estimate, the sea is calculated to form a volume of about two and one-half million billions of cubic yards, or about the five hundred and sixtieth part of the planet itself. The highest point of the land raised above the level of the sea is much less elevated than the bottom of the sea is depressed from the same level, so that the mass of the land above this level can be estimated only at about a fortieth part of the mass of the waters.

The specific gravity of sea water is greater than that of fresh. This comes from the various matters which it holds in solution. This difference varies with different seas; with the quantity of matters held in solution; with the amount of evaporation; the size and number of rivers flowing into the various seas; the ice melting into them; the currents, and various other causes. The average quantity of salts held in solution in sea water is estimated at 34.40 parts in 1,000, and this average is the same in all seas. The quantity of common salt held in solution is always a little more than three-quarters (75.786) of the total mineral matter held in solution. The salt of the sea averages, if the water is evaporated, about two inches to every fathom; so that, were the ocean dried up, a layer of salt about two hundred and thirty feet thick would remain on the bottom, or the whole salt of the sea would measure more than a thousand millions of cubic miles. This vast quantity of salt in the sea explains how the enormous beds of rock salt were formed, when the lands now exposed were covered by the waters.

Beside the oxygen and hydrogen which constitute its waters, the sea contains chlorine, nitrogen, carbon, bromine, iodine, fluorine, sulphur, phosphorus, silicon, sodium, potassium, boron, aluminium, magnesium, calcium, strontium, barium. From the various sea-weeds most of these substances can be obtained. Copper, lead, zinc, cobalt, nickel and manganese have also been found in their ashes. Iron has also been obtained from sea water, and a trace of silver also is often deposited by the magnetic current established between the sheeting of ships and the salt water. Though only a trace is thus found, yet it has been estimated that the whole waters of the ocean contain in solution two million tons of silver. In the boilers of ocean steamships, which use sea water, arsenic has also been found.

Sea water also retains dissolved air better than fresh water, and the bulk of this in ocean water is generally greater by a third than that found in river water. It varies from a fifth to a thirtieth, and gradually increases from the surface to a depth of about three hundred and twenty-five to three hundred and eighty fathoms. The uniformity in the constitution of the waters of the sea is chiefly caused by the action of the waves, which finally mix and mingle the waters into a homogeneous mass. The waves of the sea are caused chiefly by the action of the wind, and the effect continues even after the wind has ceased. One of the grandest spectacles at sea is offered by the regular movement of the waves in perfectly calm weather, when not a breath of air stirs the sails. During to the Autumnal calm under the Tropic of Cancer, these waves appear with astonishing regularity at intervals of two hundred to three hundred yards, sweep under the ship, and as far as the eye can reach, are seen advancing and passing away, as regularly as the furrows in a field. Such waves are caused by the regularity of the trade winds. The height of the waves is not the same in all seas. It is greater where the basin is deeper in proportion to the surface, and also as the water is fresher and yields easier to the impulses of the wind.

The height of waves has been variously measured. Some observers have claimed to see them over one hundred feet high, but from twenty to fifty feet is about the average of observations on the Atlantic. The breadth of a wave is calculated as fifteen times its height. Thus, a wave four feet high is sixty feet broad. The inclination of the sides of the waves varies however with the force of the wind, and with the strength of the secondary vibrations in the water, which may interfere with the primary ones. The speed of the waves is only apparent like the motion in a length of cloth shaken up and down. Floating objects do not change their relative positions, but slowly, except in rising and falling with the wave. The real movement of the sea is that of a drifting current, which is slowly formed under the action of the wind, and this is not rapid, but slow. The astronomer Airey says that every wave 100 feet wide, traversing a sea 164 fathoms in average depth, has a velocity of nearly 2,100 feet a second, or about fifteen and one-half miles an hour; a wave 674 feet, moving over a sea 1,640 fathoms deep, travels more than 69 feet a second, or nearly fifty miles an hour, and this last calculation may be taken as the average speed of storm waves in great seas. As, therefore, we can calculate the velocity of waves from their width and the known depth of the sea, we can calculate the depth of the sea from the known size and velocity of the waves. By this method the depth of the Pacific between Japan and California has been calculated from the size and speed of an earthquake wave, which was set in motion by an eruption in Japan. The accuracy of the calculation was afterward established by actual soundings.

It was formerly supposed that the disturbance of the waves did not penetrate the depth of the water, below four or six fathoms, but this has been found, on further observation, erroneous. Sand and mud have been brought up from a depth of a hundred fathoms below the surface, and experiments have shown that waves have a vertical influence 350 times their height. Thus a wave a foot high influences the bottom at a depth of 50 fathoms, and a billow of the ocean 33 feet high is felt below at a distance of 1 3/43/4 miles. At these great depths the action of the wave is perhaps imaginary, but to this reason we can ascribe the heavy swells which are often so dangerous. A hidden rock, far below the surface, arrests some moving wave and causes an eddy, which, rising to the surface, produces the "ground swells" which suddenly rise in the neighborhood of submarine banks and endanger ships. This cause also explains the tide races, which, coming from the depths of the ocean, advance suddenly upon the beaches, destroying all that opposes them. It is this cause which makes the position of light-houses upon certain reefs so dangerous. The Bell Rock house, on the Scottish coast, stands 112 feet above the rock, and yet it is often covered with the waves and foam, even after the tempest has ceased to rage. Such light-houses are often washed away; as that at Minot's Ledge, on the coast of Massachusetts, has often been. In consequence the modern method of building these structures differs from that formerly in use. The custom was to build them of solid masonry, hoping to make them strong enough to resist the waves. Now they are generally built of iron lattice open work, making the bars as slender as is consistent with the proper strength, so as to offer the least resisting surface to the rushing water. This open frame work is raised up high enough, if possible, to place the house and lantern above the reach of the body of the wave.

The force of the water in such positions is prodigious. Stephenson calculated that the sea dashed against the Bell Rock light-house with a force of 17 tons for every square yard. At breakwaters in exposed situations the sea has been known to seize blocks of stone weighing tons, and hurl them as a child would pebbles. At Cherbourg, in France, the heaviest cannon have been displaced; and at Barra Head, in the Hebrides, Stephenson states that a block of stone weighing 43 tons was driven by the breakers about two yards. At Plymouth, England, a vessel weighing 200 tons was thrown up on the top of the dike, and left there uninjured. At Dunkirk it has been found that from the dash of the breakers the ground trembles for more than a mile from the shore. Results of this kind, to which our attention is specially directed, since they affect man's work, show us what must be the effect produced by the sea, in constantly eating away the shore; altering the coast lines; changing continents, and building them up elsewhere; and suggest how much greater than what we see must have been the effects of the sea upon the land during the countless ages in which it has been at work.

The currents in the ocean, which constitute the real motion of its waters, are very important in the study of the influence of the sea upon the land. By these the circulation of the waters of the globe is carried on. The warm water of the equatorial regions seeking the poles, and a counter movement from the poles to the equator, is established. By their means a constant mingling of the waters on the face of the whole earth is maintained, and the wonderful similarity of its different portions, in their composition, appearance, and the substances held in solution, is produced. The chief causes of this grand circulation are found in the heat of the sun and in the rotation of the earth upon its axis. By the evaporation of the waters in the tropics the surface of that portion of the ocean is estimated to be lowered more than fourteen feet yearly. By this means not only is the atmosphere provided with its store of vapor, to be dispensed in rain upon the land, and thus returned again to the sea, but this lowering of the surface of the ocean, in one part, leads to the currents flowing from the others to restore the equilibrium. The same cause leading also to the circulation of the atmosphere, produces the trade winds, which aid in producing the currents in the ocean.

Now that by study and observation mankind have arrived at the conception of the form of the earth, at its general features, and can, in idea, grasp it as a whole, the opportunity is prepared for the methodical study of its parts, and their relation to each other; and this is the subject which for the first time in the history of mankind is offered to the physical geographer, with the certainty that none of his observations can be lost, but that they all are important, and can each be referred to its proper place. Another movement of the ocean is the tides. To the ancients, unacquainted with the form of the earth, its position in space, or its relations with the other bodies of the solar system, the tides were naturally inexplicable. It has been possible, only in modern times to attempt their explanation. Kepler first indicated the course to be followed; and Descartes and Newton each gave a theory; the first that of the pressure of the waters; the last, that of the attraction of the sun and moon upon the waters. This last theory is the one generally accepted, since it has been found satisfactory in most respects; yet it still has its opponents. Now, however, that the telegraph has been discovered, and a means thus afforded for instantaneous communication between observers at distant points, it has become possible to organize a simultaneous observation of the tides at various places, and eventually this will be done, so that the theory that the tides are caused by the attraction of the sun and moon will be entirely proved or rejected according as it will be found consistent with the facts observed.

In this connection an interesting instance of the different manner in which the ancients regarded natural phenomena, from that in which the moderns regard the same occurrences, is found in the fear the ancients had of the two monsters Scylla and Charybdis, which were the fabled guardians of the Straits of Messina. At present there are no straits in the Mediterranean more frequented than those of Messina. By the soundings which have been made there, these monsters had been effectually destroyed, and the whirlpools are known to be produced by the ebb and flow of the tide, causing a greater flow of water than can be accommodated by the narrow channel. The width of the channel is hardly two miles, and at low tide it has often been crossed on horseback, by swimming. The rising tide tends toward the north, from the Ionian to the Tyrrhenian sea, and the falling tide in the opposite direction. There is a strife between these currents, and on their confines eddies are formed which ships avoid, but there is no danger unless the wind blows strongly against the tide.

Besides the influence of the currents and the tides of the ocean in altering the configuration of the land, the sea is the home of innumerable forms of animal life, which are constantly laboring in the same direction. It has been truly said, that a beef bone, thrown overboard by a sailor on a ship, may form the nucleus of a new continent. The entire chalk cliffs of England were formed from the minute shells deposited by the small animals which secreted them. At their death these fell to the bottom, and thus slowly through the ages the deposit was formed. The recent deep sea dredgings have shown the sea, at all depths, is full of animal life; and as the steady fall of snow-flakes in a winter's storm, piled up by currents of wind, form the drifts, or falling quietly, cover the ground uniformly, so the sea is full of the minute shells, which, carried by currents, form banks, or, falling evenly, prepare the plains which in the future will appear, in some upheaval, to form new continents.

In the United States the peninsula of Florida is an evidence of the land produced by the labor of the coral polyp. Florida has now ceased to increase toward the east, for on this side it touches the deep waters of the gulf, and the polyps can live only in shallow water. The peninsula increases only on its southern and western coasts. The cut at the end of this chapter represents the appearance of coral islands as they first rise to the surface, before the gathering soil provides the conditions for covering them with the luxuriant vegetation of the tropics.

The cut at the head of this chapter, of an aquarium, represents a new appliance of modern times, which is a most valuable aid in our obtaining a knowledge of the habits of the animals living in the sea. In fresh water, as well as in salt, the mutual relations of the vegetable and animal life serve to keep the water from becoming stagnant. The plants secrete the carbonic acid gas, which the animals give to the water by breathing, and in so doing free the oxygen which the animals require. In keeping therefore an aquarium, the desired point is to provide such a natural proportion of vegetable and animal life as shall preserve this balance. In many of the larger museums of Europe, large aquariums have been built, and an opportunity thus afforded for the study of the various animal forms, the habits of the vegetable growths, and their relations. Some of these structures are so arranged that they surround a room which receives its light only through the water in the aquaria, and thus the spectator, without disturbing the fish, can watch them feeding and performing all their actions.

From this arrangement of the aquaria, as the light passes from the water to the eye, the spectator is not disturbed in his vision, as he is by trying to look into the water from above, by the refraction of the light. A great deal that has been learned in modern times concerning the growth of the vegetation of the sea, of the habits of the animals, of their manner of life, their food and their growth, has been obtained from the chance of observation afforded by the various aquaria. Beside the positive benefits which have thus resulted from the public aquaria, those in smaller form afford for the lover of natural history a new and interesting way of carrying on his studies. In this way also the habits of observation are formed in the young, and it is fair to believe that the spirit of inquiry thus excited will tend to increase the knowledge of the phenomena of life, and its relations to the conditions of existence.

It has been by this course that the race itself has risen from barbarism to its present degree of civilization, and with the new appliances of modern times, it is evidently impossible to limit the probabilities of advance in the future.

A few facts about the extent of our commerce will show the difference of the spirit with which the ocean is regarded in modern times, compared with that prevailing in antiquity; and the different use we have learned to make of it, from the time when the exchanges of the world were confined to a few coasters, who hardly ventured out of the sight of land. To give even the most condensed summary of the world's commerce to-day would require a series of volumes; but a few figures taken from our own will enable the reader to judge of that which is now going on all over the world, uniting the most distantly separated nations; enabling them to become acquainted with each other; and impressing them with the fact that by industry alone are the material comforts of life to be attained, and that the task before humanity is to become acquainted with the products of the world, with the forces of which it is the theatre, and learn to control them for our own benefit.

From the report of the Bureau of Statistics, for a portion of 1873, we learn that the imports and exports of the United States during eight months, ending with February, 1873, amounted to the following totals: Imported in American vessels, $104,891,248; imported in foreign vessels, $317,043,490; imported in land vehicles, $12,356,325. During the same period the domestic exports in American vessels amounted to a total of $108,246,698; in foreign vessels, $311,816,048; and in land vehicles, $5,282,949. At the same time the re-exportation of foreign products amounted in American vessels to $5,147,805; in foreign vessels to $10,938,300; and in land vehicles to $1,693,795.

The number and tonnage of American and foreign vessels engaged in the foreign trade, which entered and cleared during the twelve months ending with February, 1873, was as follows: American vessels, 10,928, carrying 3,597,474 tons; foreign vessels, 19,220, carrying 7,622,416 tons. The report of the Bureau for 1872, gives the following totals of the number of vessels and their tonnage engaged in the commerce of the United States. Upon the Atlantic and Gulf coasts, 21,940 vessels carrying 2,916,001,058 tons. On the Western rivers, 1,476 vessels carrying 354,938,052 tons. On the Northern lakes 5,339 vessels, carrying 726,105,051 tons. On the Pacific coast, 1,094 vessels carrying 161,987,050.

From the port of New York alone there are now thirteen lines of steamships plying to Europe. Of these the Anchor line has 15 steamers, with a tonnage of 36,127 tons; the Baltic Lloyds has 4 vessels of 9,200 tons; the Cardiff (a Welsh) line has three vessels of 8,000 tons; the Cunard has 23 vessels of 59,308 tons; the Holland (direct) line has two vessels of 4,000 tons; the General Transatlantic (a French line) has 5 vessels of 17,000 tons; the Hamburg has 15 vessels of 45,000 tons; the Inman line has 12 vessels of 34,811; the Liverpool and Great Western line has 7 vessels of 23,573 tons; the North German line has 20 vessels of 60,000 tons; the National line has 12 vessels of 50,062 tons; the State line has 3 vessels of 7,500 tons; and the White Star line has 6 vessels of 23,064 tons. Beside these ships, the thirteen companies are building from 30 to 40 more steamers to meet the demand for freight.

The ocean has thus become almost a steam ferry; almost every day a steamer leaves for Europe. With this knowledge of how far we have progressed in becoming acquainted with the ocean, it will be well to consider for a moment how much still remains for us to explore. In the middle ages, and even down to modern times, the maps of the world represented all unknown lands as inhabited by monsters; but every voyage made by discoverers has contracted the limits of these fables, until they have finally about disappeared. Still at the North Pole and in the Antarctic regions areas extending over a space of 2,900,000 and 8,700,000 square miles, respectively, have been, up to this time, unvisited. The icebergs and mountains of ice have kept them from our accurate investigations. The difficulties of such a sea are well shown in the adjoining illustration.

Discoveries have also to be made in the interiors of Africa, Asia, South America and Australia before the civilized portions of the race can claim a complete knowledge of the earth, their common dwelling-place. Every year, however, the portions unexplored grow smaller and smaller, so that we are justified in believing that eventually the whole world will be known to us, from actual observation.

Another difference which our extended knowledge of the world has produced is this: The mariner now approaching an unknown coast does not fear to meet monsters, but looks out for the light-house, the light-ships, the buoys, and other evidences of civilization, by which the dangers of the coast are pointed out to the voyager. As a contrast with some of the pictures already given, representing the approach to the land of the early explorers, the illustration of the light-ship will show how differently to-day a voyage approaches its termination. Instead of looking out for enemies, and preparing weapons for use, a package of newspapers and letters is got ready, and the news boat, which lies ready at hand, is prompt to seize them, and hasten with these to spread the news of another safe arrival. It is thus that science, which is gradually preparing the means for converting the globe into one great organism for the benefit of mankind, points out the way for making it the abode of that harmony, peace and plenty which has been dreamed of by the poets of all time. For this it is only necessary that our moral progress should keep pace with our advance in knowledge. The globe will never become the abode of perfect harmony until men are united in a universal league of justice and peace. And in aiding toward the production of this most desirable consummation, what has been here written will show how important has been the part taken by the ocean.