Physical Geography of the Sea and its Meteorology/Chapter 1
THE
PHYSICAL GEOGRAPHY OF THE SEA,
AND ITS METEOROLOGY.
CHAPTER 1.
1-68.—THE SEA. AND THE ATMOSPHERE.
§ 1.The two oceans of air and water.—Our planet is invested with two great oceans; one visible, the other invisible; one is underfoot, the other overhead; one entirely envelops it, the other covers about two-thirds of its surface. All the water of the one weighs about 400 times as much as all the air of the other.
2.Their meeting.—It is at the bottom of this lighter ocean where the forces which we are about to study are brought into play. This place of meeting is the battle-field of nature, the dwelling-place of man; it is the scene of the greatest conflicts which he is permitted to witness, for here rage in their utmost fury the powers of sea, earth, and air; therefore, in treating of the Physical Geography of the sea, we must necessarily refer to the phenomena which are displayed at the meeting of these two oceans. Let us, therefore, before entering either of these fields for study, proceed first to consider each one in some of its most striking characteristics. They are both in a state of what is called unstable equilibrium; hence the currents of one and the winds of the other.
3.Their depth.—As to their depth, we know very little more of the one than of the other; but the conjecture that the average depth of the sea does not much exceed four miles is probably as near the truth as is the commonly received opinion that the height of the atmosphere does not exceed fifty miles. If the air were, like water, non-elastic, and not more compressible than this non-elastic fluid, we could sound out the atmospherical ocean with the barometer, and gauge it by its pressure. The mean height of the barometer at the level of the sea in the torrid and temperate zones, is about 30 inches. Now, it has been ascertained that, if we place a barometer 87 feet above the level of the sea, its average height will be reduced from 30.00 in. to 29.90 in.; that is, it will be diminished one-tenth of an inch, or the three hundredth part of the whole; consequently, by going up 300 X 87 ( = 26,100) feet, the barometer, were the air non-elastic, would stand at 0. It would then be at the top of the atmosphere. The height of 26,100 feet is just five miles lacking 300 feet.
4. Weight of the atmosphere.—But the air is elastic, and very unlike water. That at the bottom is pressed down by the superincumbent air with the force of about 15 pounds to the square inch, while that at the top is inconceivably light. If, for the sake of explanation, we imagine the lightest down, in layers of equal weight and ten feet thick, to be carded into a pit several miles deep, we can readily perceive how that the bottom layer, though it might have been ten feet thick when it first fell, yet with the weight of the accumulated and superincumbent mass, it might now, the pit being full, be compressed into a layer of only a few inches in thickness, while the top layer of all, being uncompressed, would be exceedingly light, and still ten feet thick; so that a person ascending from the bottom of the pit would find the layers of equal weight thicker and thicker until he reached the top. So it is with the barometer and the atmosphere: when it is carried up in the air through several strata of 87 feet, the observer does not find that it falls a tenth of an inch for every successive 87 feet upward through which he may carry it. To get it to fall a tenth of an inch, he must carry it higher and higher for every successive layer.
5. Three-fourths below the mountain tops.—More than three-fourths of the entire atmosphere is below the level of the highest mountains; the other fourth is rarefied and expanded in consequence of the diminished pressure, until the height of many miles be attained. From the reflection of the sun's rays after he has set, or before he rises above the horizon, it is calculated that this upper fourth part must extend at least forty or forty-five miles higher. 6. Its height.—At the height of 26,000 miles from the earth, the centrifugal force would counteract gravity; consequently, all ponderable matter that the earth carries with it in its diurnal revolution must be within that distance, and consequently the atmosphere cannot extend beyond that. This limit, however, has been greatly reduced, for Sir John Herschel has shown, by balloon observations,[1] that at the height of 80 or 90 miles there is a vacuum far more complete than any which we can produce by any air-pump. In 1783 a large meteor, computed to be half a mile in diameter and fifty miles from the earth, was heard to explode. As sound cannot travel through vacuum, it was inferred that the explosion took place within the limits of the atmosphere. Herschel concludes that the aerial ocean is at least 50 miles deep.
7. Data conjectural.—The data from which we deduce our estimate, both as to the mean height of the atmosphere and average depth of the ocean, are, to some extent, conjectural; consequently, the estimates themselves must be regarded as approximations, but sufficiently close, nevertheless, for the present purposes of this work.
8. Analysis of air.—Chemists who have made the analysis, tell us that, out of 100 parts of atmospheric air, 99.5 consist of oxygen and nitrogen, mixed in the proportion of 21 of oxygen to 79 of nitrogen by volume, and of 23 to 77 by weight. The remaining half of a part consists of .05 of carbonic acid and .45 of aqueous vapour.
9. Information respecting the depth of the ocean.—The average depth of the ocean has been variously computed by astronomers, from such arguments as the science affords, to be from 26 to 11 miles. About ten years ago I was permitted to organize and set on foot in the American navy a plan for "sounding out" the ocean with the plummet.[2] Other navies, especially the English, have done not a little in furtherance of that object. Suffice it to say that, within this brief period, though the undertaking has been by no means completed—no, not even to the tenth part—yet more knowledge has been gained concerning the depths and bottom of the deep sea, than all the world had before acquired in all previous time.
10. Its probable depth. "The system of deep-sea soundings thus inaugurated does not thus far authorize the conclusion that the overage depth of ocean water is more than three or four miles (§ 3) nor have any reliable soundings yet been made in water over five miles deep.
11. Relation between its depth and the waves of the sea.—In very shallow pools, where the water is not more than a few inches deep, the ripples or waves, as all of us, when children, have observed, are small; their motion, also, is slow. But when the water is deep, the waves are larger and more rapid in their progress, thus indicating the existence of a numerical relation between their breadth, height, and velocity, and the depth of the water. It may be inferred, therefore, that if we knew the size and velocity of certain waves, we could compute the depth of the ocean.
12. Airy's wave tables.—Such a computation has been made, and we have the authority of Mr. Airy,[3] the Astronomer Royal, that waves of given breadths will travel in water of certain depths with the velocities as per table:
| Depth of the Water in Feet. |
Breadth of the wave in feet. | |||||||
| 1 | 10 | 100 | 1000 | 10,000 | 100,000 | 1,000,000 | 10,000,000 | |
| Corresponding Velocity of Wave per Hour in Miles. | ||||||||
| 1 | 1.54 | 3.81 | 3.86 | 3.86 | 3.86 | 3.86 | 3.86 | 3.86 |
| 10 | 1.54 | 4.87 | 11.51 | 12.21 | 12.22 | 12.22 | 12.22 | 12.22 |
| 100 | 1.54 | 4.87 | 15.18 | 36.40 | 38.64 | 38.66 | 38.66 | 38.66 |
| 1,000 | 1.54 | 4.87 | 15.18 | 48.77 | 115.11 | 122.18 | 122.27 | 122.27 |
| 10,000 | 1.54 | 4.87 | 15.18 | 48.77 | 154.25 | 364.92 | 386.40 | 386.66 |
| 100,000 | 1.54 | 4.87 | 15.18 | 48.77 | 154.25 | 487.79 | 1150.00 | 1222.70 |
13. The earthquake of Simoda.—Accident has afforded us an opportunity of giving a quasi practical application to Mr. Airy's formulæ. On the 23rd of December, 1854, at 9.45 a.m.,[4] the first shocks of an earthquake were felt on board the Russian frigate "Diana," as she lay at anchor in the harbour of Simoda, not far from Jeddo, in Japan. In fifteen minutes afterwards (10 o'clock), a large wave was observed rolling into the harbour, and the water on the beach to be rapidly rising. The town, as seen from the frigate, appeared to be sinking. This wave was followed by another, and when the two receded—which was at 10h. 15m.—there was not a house, save an unfinished temple, left standing in the village. These waves continued to come and go until 2.30 P.M., during which time the frigate was thrown on her beam ends five times. A piece of her keel 81 feet long was torn off, holes were knocked in her by striking on the bottom, and she was reduced to a wreck. In the course of five minutes the water in the harbour fell, it is said, from 23 to 3 feet, and the anchors of the ship were laid bare. There was a great loss of life; many houses were washed into the sea, and many junks carried up—one two miles inland—and dashed to pieces on the shore. The day was beautifully fine, and no warning was given of the approaching convulsion; the barometer standing at 29.87 in., thermometer 58°; the sea perfectly smooth when its surface was broken by the first wave. It was calm in the morning, and the wind continued light all day.
14. The propagation of leaves by it.—In a few hours afterwards, at San Francisco and San Diego, the tide-gauges showed that several well-marked and extraordinary waves had arrived off the coast of California.[5] The origin of these waves, and those which destroyed the town of Simoda, in Japan, and wrecked the "Diana," was doubtless the same. But where was their birthplace? Supposing it to be near the coasts of Japan, we may, with the tide-gauge observations in California and Mr. Airy's formulæ, calculate the average depth of the sea along the path of the wave from Simoda both to San Francisco and San Diego.
15. Their breadth and velocity.—Supposing the waves to have taken up their line of march from some point along the coast of Japan, the San Francisco wave, having a breadth of 256 miles, had a velocity of 438 miles an hour; while the breadth of the San Diego wave was 221 miles, and its rate of travel 427 miles an hour.
16. Average depth of the North Pacific.— Admitting these premises—which are partly assumed—to be correct, then, according to Airy's formulæ, the average depth of the North Pacific between Japan and California is, by the path of the San Francisco wave, 2149 fathoms, by the San Diego, 2034 (say 2½ miles).
17. Specific gravity of sea-water.—At the temperature of 60°, the specific gravity of average sea-water is 1.0272,[6] and the weight of a cubic foot is 64.003 lbs.
18. Of air.—With the barometer at 30 in. and the thermometer at 32°, the weight of a cubic foot of dry atmospheric air is 1.291 oz., and its specific gravity .00129. Such is the difference in weight between the two elements, the phenomena of which give the physical geography of the sea its charms.
19. Unequal distribution of light, land, and air.—There is in the northern hemisphere more land, less sea, more fresh water, more atmospheric air, and a longer annual duration of sunlight, than there is in the southern. And though the two hemispheres receive annually the same amount of heat directly from the sun, yet the northern, without growing cooler, dispenses the greater quantity by radiation.
20. The sun longer in northern declination.—In his annual round, the sun tarries a week (7¾ days) longer on the north than he does on the south side of the equator, and consequently the antarctic night and its winter are longer than the polar winter and night of the arctic regions. The southern hemisphere is said also to be cooler, but this is true only as to its torrid and temperate zones. In the summer of the southern hemisphere the sun is in perigee, and during the course of a diurnal revolution there the southern half of our planet receives more heat than the northern half during the same period of our summer. This difference, however, Sir John Herschel rightfully maintains is compensated by the longer duration of the northern summer. Therefore, admitting the total quantity of heat annually impressed upon the earth by the sun to be equally divided between the two hemispheres, it does not follow that their temperature should be the same, for their powers of radiation may be very different. The northern hemisphere having most land, radiates the more freely—the land and sea breezes tell us that the land dispenses heat more freely than the sea by radiation—but the northern hemisphere is prevented in two ways from growing cooler than the southern:—1. by the transfer of heat in the latent form with the vapours from the southern seas;—2. by the transfer of heat in the sensible form, by currents such as the Gulf Stream, et al., from one climate to another in our hemisphere. Hence we infer that the southern hemisphere is in certain zones cooler than the northern, not by reason of its short summer or long winter, but it is the cooler chiefly on account of the latent heat which is brought thence by vapour, and set free here by condensation.
21. England about the pole of hemisphere with most land.—Within the torrid zone the land is nearly equally divided north and south of the equator, the proportion being as 5 to 4. In the temperate zones, however, the north with its land is thirteen times in excess of the south. Indeed, such is the inequality in the distribution of land over the surface of the globe that the world may be divided into hemispheres consisting, the one with almost all the land in it, except Australia and a slip of America lying south of a line drawn from the desert of Atacama to Uruguay; England is the centre of this, the dry hemisphere. The other, or aqueous hemisphere, contains all the great waters except the Atlantic Ocean; New Zealand is the nearest land to its centre.
22. Effects of inequality in distribution of land and water.—This unequal distribution of land, light, air, and water is suggestive. To it we owe, in a measure, the different climates of the earth. Were it different, they would be different also; were it not for the winds, the vapours that rise from the sea would from the clouds be returned in showers back to the places in the sea whence they came; on an earth where no winds blow we should have neither green pastures, still waters, nor running brooks to beautify the landscape. Were there no currents in the sea, nor vertical movements in the air, the seasons might change, but climates would be a simple affair, depending solely on the declination of the sun in the sky.
23. Quantity of fresh water in American lakes.—About two-thirds of all the fresh water on the surface of the earth is contained in the great American lakes; and though there be in the northern, as compared with the southern hemisphere, so much less sea surface to yield vapour, so much more land to swallow up rain, and so many more plants to drink it in, yet the fresh-water courses are far more numerous and copious on the north than they are on the south side of the equator. 24. Southern seas the boiler, and northern lands the condenser.—These facts have suggested the comparison in which the southern hemisphere has been likened to the boiler and the northern to the condenser of the steam-engine. This vast amount of steam or vapour rising up in the extra-tropical regions of the south, expels the air thence, causing the barometer to show a much less weight of atmosphere on the polar side of 40° S., than we find in corresponding latitudes north.
25. Offices of the atmosphere.—The offices of the atmosphere are many, marvellous, and various. Though many of them are past finding out, yet, beautiful to contemplate, they afford most instructive and profitable themes for meditation.
26. Dr. Buist.—When this system of research touching the physics of the sea first began—when friends were timid and co-labourers few, the excellent Dr. Buist stood up as its friend and champion in India; and by the services he thus rendered, entitled himself to the gratitude of all who, with me, take delight in the results which have been obtained. The field which it was proposed to occupy—the firstlings of which were gathered in this little book—was described by him in glowing terms, and with that enthusiasm which never fails to inspire zeal. They are apropos, and it is a pleasure to repeat the substance of them.
27. The sea and the atmosphere contrasted.—"The weight of the atmosphere is equal to that of a solid globe of lead sixty miles in diameter. Its principal elements are oxygen and nitrogen gases, with a vast quantity of water suspended in them in the shape of vapour, and commingled with these a quantity of carbon in the shape of fixed air, equal to restore from its mass many fold, the coal that now exists in the world. In common with all substances, the ocean and the air are increased in bulk, and, consequently diminished in weight, by heat; like all fluids, they are mobile, tending to extend themselves equally in all directions, and to fill up depressions wherever vacant space will admit them; hence in these respects the resemblance betwixt their movements. Water is not compressible or elastic, and it may be solidified into ice, or vaporized into steam; the air is elastic; it may be condensed to any extent by pressure, or expanded to an indefinite degree of tenuity by pressure being removed from it; it is not liable to undergo any change in its constitution beyond these, by any of the ordinary influences by which it is affected.
28. Influence of the sun.—"These facts are few and simple enough; let us see what results arise from them: As the constant exposure of the equatorial regions of the earth to the sun must necessarily there engender a vast amount of heat, and as his absence from the polar regions must in like manner promote an infinite accumulation of cold, to fit the entire earth for a habitation to similar races of beings, a constant interchange and communion betwixt the heat of the one, and the cold of the other, must be carried on. The ease and simplicity with which this is effected surpass all description. The air, heated near the equator by the overpowering influences of the sun, is expanded and lightened; it ascends into upper space, leaving a partial vacuum at the surface to be supplied from the regions adjoining. Two currents from the poles toward the equator are thus established at the surface, while the sublimated air, diffusing itself by its mobility, flows in the upper regions of space from the equator toward the poles. Two vast whirlpools are thus established, constantly carrying away the heat from the torrid toward the icy regions, and, there becoming cold by contact with the ice, they carry back their gelid freight to refresh the torrid zone.
29. Of diurnal rotation.—"Did the earth, as was long believed, stand still while the sun circled around it, we should have had directly from north and south two sets of meridional currents blowing at the surface of the earth toward the equator; in the upper regions we should have had them flowing back again to the place whence they came. On the other hand, were the heating and cooling influences just referred to to cease, and the earth to fail in impressing its own motion on the atmosphere, we should have a furious hurricane rushing round the globe at the rate of 1000 miles an hour—tornadoes of ten times the speed of the most violent now known to us, sweeping everything before them. A combination of the two influences, modified by the friction of the earth, which tends to draw the air after it, gives us the trade-winds, which, at the speed of from ten to twenty miles an hour, sweep round the equatorial region of the globe unceasingly.
30. Currents.—"Impressed with the motion of the air, constantly sweeping its surface in one direction, and obeying the same laws of motion, the great sea itself would be excited into currents similar to those of the air, were it not walled in by continents and subjected to other control. As it is, there are constant currents flowing from the torrid toward the frigid zone to supply the vast amount of vapour there drained off, while other whirlpools and currents, such as the gigantic Gulf Stream, come to preform their part in the same stupendous drama. The waters of this vast ocean river are, to the north of the tropic, greatly warmer than those around; the climate of every country it approaches is improved by it, and the Laplander is enabled by its means to live and cultivate his barley in a latitude which, everywhere else throughout the world, is condemned to perpetual sterility. There are other laws which the great sea obeys which peculiarly adapt it as the vehicle of interchange of heat and cold betwixt those regions where either exists in excess.
31. Icebergs.—"In obedience to these laws water warmer than ice attacks the basis and saps the foundations of the icebergs—themselves gigantic glaciers, which have fallen from the mountains into the sea, or which have grown to their present size in the shelter of bays and estuaries, and by accumulations from above. Once forced from their anchorage, the first storm that arises drifts them to sea, where the beautiful law which renders ice lighter than the warmest water, enables it to float, and drifts southward a vast magazine of cold to cool the tepid water which bears it along—the evaporation at the equator causing a deficit, the melting and accumulation of the ice in the frigid zone giving rise to an excess of accumulation, which tends, along with the action of the air and other causes, to institute and maintain the transporting current. These stupendous masses, which have been seen at sea in the form of church spires, and Gothic towers, and minarets, rising to the height of from 300 to 600 feet, and extending over an area of not less than six square miles, the masses above water being only one-tenth of the whole, are often to be found within the tropics.
32. Mountain ranges.—"But these, though among the most regular and magnificent, are but a small number of the contrivances by which the vast and beneficent ends of nature are brought about. Ascent from the surface of the earth produces the same change, in point of climate, as an approach to the poles; even under the torrid zone mountains reach the line of perpetual congelation at nearly a third less altitude than the extreme elevation which they sometimes attain. At the poles snow is perpetual on the ground, and at the different intervening latitudes reaches some intermediate point of congelation betwixt one and 20,000 feet. In America, from the line south to the tropics, as also, as there is now every reason to believe, in Africa within similar latitudes, vast ridges of mountains, covered with perpetual snow, run northward and southward in the line of the meridian right across the path of the trade-winds. A similar ridge, though of less magnificent dimensions, traverses the peninsula of Hindoostan, increasing in altitude as it approaches the line, attaining an elevation of 8500 feet at Dodabetta, and about 6000 in Ceylon. The Alps in Europe, and the gigantic chain of the Himalayas in Asia, both far south in the temperate zone, stretch from east to west, and intercept the aerial current from the north. Others of lesser note, in the equatorial or meridional, or some intermediate direction, cross the paths of the atmospherical currents in every direction, imparting to them fresh supplies of cold, as they themselves obtain from them warmth in exchange: in strictness the two operations are the same.
33. Water.—"Magnificent and stupendous as are the effects and results of the water and of air acting independently on each other, in equalizing the temperature of the globe, they are still more so when combined. One cubic inch of water, when invested with a sufficiency of heat, will form one cubic foot of steam—the water before its evaporation, and the vapour which it forms being exactly of the same temperature; though in reality, in the process of conversion, 1100 degrees of heat have been absorbed or carried away from the vicinage, and rendered latent or imperceptible; this heat is returned in a sensible and perceptible form the moment the vapour is converted once more into water. The general fact is the same in the case of vapour carried off by dry air at any temperature that may be imagined; for, down far below the freezing-point, evaporation proceeds uninterruptedly.
34. Latent heat.—"The air, heated and dried as it sweeps over the arid surface of the soil, drinks up by day myriads of tons of moisture from the sea—as much, indeed, as would, were no moisture restored to it, depress its whole surface at the rate of eight or ten feet annually. The quantity of heat thus converted from a sensible or perceptible to an insensible or latent state is almost incredible. The action equally goes on, and with the like results, over the surface of the earth, where there is moisture to be withdrawn. But night and the seasons of the year come round, and the surplus temperature, thus withdrawn and stored away at the time it might have proved superfluous or inconvenient, is rendered back so soon as it is required; thus the cold of night and the rigour of winter are modified by the heat given out at the point of condensation by dew, rain, hail, and snow.
35. Effects upon the earth.—"The earth is a bad conductor of heat; the rays of the sun, which enter its surface and raise the temperature to 100° or 150°, scarcely penetrate a foot into the ground; a few feet down, the warmth of the ground is nearly the same night and day. The moisture which is there preserved free from the influence of currents of air is never raised into vapour; so soon as the upper stratum of earth becomes thoroughly dried, capillary action, by means of which all excess of water was withdrawn, ceases; so that, even under the heats of the tropics, the soil two feet down will be found, on the approach of the rains, sufficiently moist for the nourishment of plants. The splendid flowers and vigorous foliage which burst forth in May, when the parched soil would lead us to look for nothing but sterility, need in no way surprise us; fountains of water, boundless in extent and limited in depth only by the thickness of the soil which contains them, have been set aside and sealed up for their use, beyond the reach of those thirsty winds or burning rays which are suffered to carry off only the water which is superfluous, and would be pernicious. They remove it to other lands, where its agency is required, or treasure it up, as the material of clouds and dew, in the crystal vault of the firmament, the source, when the fitting season comes round again, of those deluges of rain which provide for the wants of the year. Such are some of the examples which may be supplied of general laws operating over nearly the whole surface of the terraqueous globe. Among the local provisions ancillary to these are the monsoons of India, and the land and sea breezes prevalent throughout the tropical coasts.
36. The tides.—"We have not noticed the tides, which, obedient to the sun and moon, daily convey two vast masses of water round the globe, and which twice a month, rising to an unusual height, visit elevations which otherwise are dry. During one half of the year the highest tides visit us by day, the other half by night; and at Bombay, at spring tide, the depths of the two differ by two or three feet from each other. The tides simply rise and fall, in the open ocean, to an elevation of two or three feet in all; along our shores, and up gulfs and estuaries, they sweep with the violence of a torrent, having a general range of ten or twelve feet—sometimes, as at Fundy, in America, at Brest and Milford Haven, in Europe, to a height of from forty to sixty feet. The tides sweep our shores from filth, and purify our rivers and inlets, affording to the residents of our islands and continents the benefits of a bi-diurnal ablution, and giving a health, and freshness, and purity wherever they appear. Obedient to the influence of bodies many millions of miles removed from them, their subjection is not the less complete; the vast volume of water, capable of crushing by its weight the most stupendous barriers that can be opposed to it, and bearing on its bosom the navies of the world, impetuously rushing against our shores, gently stops at a given line, and flows back again to its place when the word goes forth, 'Thus far shalt thou go, and no farther;' and that which no human power or contrivance could have repelled, returns at its appointed time so regularly and surely that the hour of its approach, and measure of its mass, may be predicted with unerring certainty centuries beforehand.
37. Hurricanes.—"The hurricanes which whirl with such fearful violence over the surface, raising the waters of the sea to enormous elevations, and submerging coasts and islands, attended as they are by the fearful attributes of thunder and deluges of rain, seem requisite to deflagrate the noxious gases which have accumulated, to commingle in one healthful mass the polluted elements of the air, and restore it fitted for the ends designed for it. We have hitherto dealt with the sea and air—the one the medium through which the commerce of all nations is transported, the other the means by which it is moved along—as themselves the great vehicles of moisture, heat, and cold throughout the regions of the world—the means of securing the interchange of these inestimable commodities, so that excess may be removed to where deficiency exists, deficiency substituted for excess, to the unbounded advantage of all. This group of illustrations has been selected because they are the most obvious, the most simple, and the most intelligible and beautiful that could be chosen.
38. Powers of the air.—"We have already said that the atmosphere forms a spherical shell, surrounding the earth to a depth which is unknown to us, by reason of its growing tenuity, as it is released from the pressure of its own superincumbent mass. Its upper surface cannot "be nearer to us than fifty, and can scarcely be more remote than five hundred miles. It surrounds us on all sides, yet we see it not; it presses on us with a load of fifteen pounds on every square inch of surface of our bodies, or from seventy to one hundred tons on us in all, yet we do not so much as feel its weight. Softer than the finest down, more impalpable than the finest gossamer, it leaves the cobweb undisturbed, and scarcely stirs the lightest flower that feeds on the dew it supplies; yet it bears the fleets of nations on its wings around the world, and crushes the most refractory substances with its weight. When in motion, its force is sufficient to level with the earth the most stately forests and stable buildings, to raise the waters of the ocean into ridges like mountains, and dash the strongest ships to pieces like toys. It warms and cools by turns the earth and the living creatures that inhabit it. It draws up vapours from the sea and land, retains them dissolved in itself or suspended in cisterns of clouds, and throws them down again, as rain or dew, when they are required. It bends the rays of the sun from their path to give us the aurora of the morning and twilight of evening; it disperses and refracts their various tints to beautify the approach and the retreat of the orb of day. But for the atmosphere, sunshine would burst on us in a moment and fail us in the twinkling of an eye, removing us in an instant from midnight darkness to the blaze of noon. We should have no twilight to soften and beautify the landscape, no clouds to shade us from the scorching heat; but the bald earth, as it revolved on its axis, would turn its tanned and weakened front to the full and unmitigated rays of the lord of day.
39. Its functions.—"The atmosphere affords the gas which vivifies and warms our frames; it receives into itself that which has been polluted by use, and is thrown off as noxious. It feeds the flame of life exactly as it does that of the fire. It is in both cases consumed, in both cases it affords the food of consumption, and in both cases it becomes combined with charcoal, which requires it for combustion, and which removes it when combustion is over. It is the girdling encircling air that makes the whole world kin. The carbonic acid with which to-day our breathing fills the air, to-morrow seeks its way round the world. The date-trees that grow round the falls of the Nile will drink it in by their leaves; the cedars of Lebanon will take of it to add to their stature; the cocoa-nuts of Tahiti will grow rapidly upon it; and the palms and bananas of Japan will change it into flowers. The oxygen we are breathing was distilled for us some short time ago by the magnolias of the Susquehanna and the great trees that skirt the Orinoco and the Amazon; the giant rhododendrons of the Himalayas contributed to it, and the roses and myrtles of Cashmere, the cinnamon-tree of Ceylon, and the forest, older than the flood, that lies buried deep in the heart of Africa, far behind the Mountains of the Moon, gave it out. The rain we see descending was thawed for us out of the icebergs which have watched the Polar Star for ages, or it came from snows that rested on the summits of the Alps, but which the lotus lilies have soaked up from the Nile, and exhaled as vapour again into the ever-present air."
40. The operations of water.—There are processes no less interesting going on in other parts of this magnificent field of research. Water is nature's carrier. With its currents it conveys heat away from the torrid zone and ice from the frigid; or, bottling the caloric away in the vesicles of its vapour, it first makes it impalpable, and then conveys it, by unknown paths, to the most distant parts of the earth. The materials of which the coral builds the island, and the sea-conch its shell, are gathered by this restless leveller from mountains, rocks, and valleys in all latitudes. Some it washes down from the Mountains of the Moon, or out of the gold-fields of Australia, or from the mines of Potosi, others from the battle-fields of Europe, or from the marble quarries of ancient Greece and Rome. These materials, thus, collected and carried over falls or down rapids, are transported from river to sea, and delivered by the obedient waters to each insect and to every plant in the ocean at the right time and temperature, in proper form, and in due quantity.
41. Its marvellous powers.—Treating the rocks less gently, it grinds them into dust, or pounds them into sand, or rolls and rubs them until they are fashioned into pebbles, rubble, or boulders: the sand and shingle on the sea-shore are monuments of the abrading, triturating power of water. By water the soil has been brought down from the hills and spread out into valleys, plains, and fields for man's use. Saving the rocks on which the everlasting hills are established, everything on the surface of our planet seems to have been removed from its original foundation and lodged in its present place by water. Protean in shape, benignant in office, water, whether fresh or salt, solid, fluid, marvellous in its powers.
42. It caters on land for insects of the sea.—It is one of the chief agents in the manifold workshops in which and by which the earth has been made a habitation fit for man. Circulating in veins below the surface, it pervades the solid crust of the earth in the fulfilment of its offices; passing under the mountains it runs among the hills and down through the valley's in search of pabulum for the moving creatures that have life in the sea. In rivers and in rain it gathers up by ceaseless lixiviation food for the creatures that wait upon it. It carries off from the land whatever of solid matter the sea in its economy requires.
43. Leaching.—The waters which dash against the shore, which the running streams pour into the flood, or with which the tides and currents scour the bottom of their channel ways, have soaked from the soil, or leached out of the disintegrated materials which strew the beach or line the shores, portions of every soluble ingredient known in nature. Thus impregnated, the laughing, dancing waters come down from the mountains, turning wheels, driving machinery, and serving the manifold purposes of man. At last they find their way into the sea, and so make the lye of the earth brine for the ocean.
44. Solid ingredients.—Iron, lime, silver, sulphur, and copper, silex, soda, magnesia, potash, chlorine, iodine, bromine, ammonia, are all found in sea-water; some of them in quantities too minute for the nicest appliances of the best chemists to detect, but which, nevertheless, are elaborated therefrom by physical processes the most exquisite.
45. Quantity of silver in the sea.—By examining in Valparaiso the copper that had been a great while on the bottom of a ship, the presence of silver, which it obtained from the sea, was detected in it. It was in such quantities as to form the basis of a calculation, by which it would appear that there is held in solution by the sea a quantity of silver sufficient to weigh no less than two hundred million tons, could it all, by any process, be precipitated and collected into a separate mass.
46. Its inhabitants—their offices.—The salts of the sea, as its solid ingredients may be called, can neither be precipitated on the bottom, nor taken up by the vapours, nor returned again by the rains to the land; and, but for the presence in the sea of certain agents to which has been assigned the task of collecting these ingredients again, in the sea they would have to remain. There, accumulating in its waters, they would alter the quality of the brine, injure the health of its inhabitants, retard evaporation, change climates, and work endless mischief upon the fauna and the flora of both sea, earth, and air. But in the oceanic machinery all this is prevented by compensations the most beautiful, and adjustments the most exquisite. As in the atmosphere the plants are charged with the office of purifying the air by elaborating into vegetable tissue and fibre the impurities which the animals are continually casting into it, so also to the mollusks, to the madrepores, and insects of the sea, has been assigned the office of taking out of its waters and making solid again all this lixiviated matter as fast as the dripping streams and searching rains discharge it into the ocean.
47. Monuments of their industry.—As to the extent and magnitude of this endless task some idea may be formed from the coral islands, the marl beds, the shell banks, the chalk cliffs, and other marine deposits which deck the sea shore or strew the land.
48. Analysis of sea-water.—Fresh water is composed of oxygen and hydrogen gas in the proportion by weight of 1 to 8; and the principal ingredients which chemists, by treating small samples of sea-water in the laboratory, have found in a thousand grains, are—
Water....................... 962.0 grains
Chloride of Sodium........... 27.1 grains
Chloride of Magnesium......... 5.4 "
Chloride of Potassium......... 0.4 "
Bromide of Magnesia........... 0.1 "
Sulphate of Magnesia.......... 1.2 "
Sulphate of Lime.............. 0.8 "
Carbonate of Lime............. 0.1 "
Leaving a residuum of......... 2.9 " = 1000,
consisting of sulphuretted hydrogen gas, hydrochlorate of ammonia, etc., etc., in various quantities and proportions, according to the locality of the specimen.
49. Proportion of water to the mass of the earth.—If we imagine the whole mass of the earth to be divided into 1786 equal parts by weight, then the weight of all the water in the sea would, according to an estimate by Sir John Herschel, be equivalent to one of such parts. Such is the quantity, and such some of the qualities of that delightful fluid to which, in the laboratories and workshops of nature, such mighty tasks, such important offices, such manifold and multitudinous powers have been assigned.
50. The three great oceans.—This volume of water, that out-weighs the atmosphere (§1) about 400 times, is divided into three great oceans, the Atlantic, the Pacific, and the Arctic; for in the rapid survey which in this chapter we are taking of the field before us, the Indian and Pacific oceans may be regarded as one.
51. The Atlantic.—The Atlantic Ocean, with its arms, is supposed to extend from the Arctic to the Antarctic—perhaps from pole to pole; but, measuring from the icy barrier of the north to that of the south, it is about 9000 miles in length, with a mean breadth of 2700 miles. It covers an area of about 25,000,000 square miles. It lies between the Old World and the New: passing beyond the "stormy capes," there is no longer any barrier, but only an imaginary line to separate its waters from that great southern waste in which the tides are cradled.
52. Its tides.—The young tidal wave, rising in the circumpolar seas of the south, rolls thence into the Atlantic, and in 12 hours after passing the parallel of Cape Horn, it is found pouring its flood into the Bay of Fundy.
53. Its depths.—The Atlantic is a deep ocean, and the middle its deepest part, therefore the more favourable (§ 13) to the propagation of this wave.
54. Contrasted with the Pacific.—The Atlantic Ocean contrasts very strikingly with the Pacific. The greatest length of one lies east and west; of the other, north and south. The currents of the Pacific are broad and sluggish, those of the Atlantic swift and contracted. The Mozambique current, as it is called, has been found by navigators in the South Pacific to be upwards of 1600 miles wide—nearly as broad as the Gulf Stream is long. The principal currents in the Atlantic run to and fro between the equator and the Northern Ocean. In the Pacific they run between the equator and the southern seas. In the Atlantic the tides are high, in the Pacific they are low. The Pacific feeds the clouds with vapours, and the clouds feed the Atlantic with rain for its rivers. If the volume of rain which is discharged into the Pacific and on its slopes be represented by 1, that discharged upon the hydrographical basin of the Atlantic into the Atlantic would be represented by 5. The Atlantic is crossed daily by steamers, the Pacific rarely. The Atlantic washes the shores of the most powerful, intelligent, and Christian nations; but a pagan or a heathen people in the countries to which the Pacific gives drainage are like the sands upon its shores for multitude. The Atlantic is the most stormy sea in the world, the Pacific the most tranquil.
55. The Telegraphic Plateau.—Among the many valuable discoveries to which these researches touching the physics of the sea have led, none perhaps is more interesting than the Telegraphic Plateau of the Atlantic, and the fact that the bottom of the deep sea is lined with its own dead, whose microscopic remains are protected from the abrading action of its currents and the violence of its waves by cushions of still water.
56. New routes for an Atlantic Telegraph.—The idea of a telegraph from England or Ireland along this plateau to America, seems after the splendid failure of 1858 to have been abandoned, chiefly however on account of the electrical difficulties which stand in the way of so long a circuit. Other routes with shorter circuits are now proposed: these are engaging the attention of enlightened governments in Europe, and of enterprising men on both sides of the Atlantic.
57. The Greenland route.—A line via Iceland and Greenland to Labrador, and thence overland to Canada and the United States, is attracting attention in England. The Admiralty have despatched Captain McClintock in the "Fox," of Arctic renown, to run a line of deep-sea soundings along this route.
58. The French route.—Another line from France, via the Western Islands to St. Pierre Miquelon, a French fishing-station off Newfoundland, and thence to the United States, is attracting the attention of the French people. Their emperor has given his sanction with the most liberal encouragement.
59. Their length of circuit.—The longest reach by the Greenland route may require a circuit not exceeding 400 or 500 miles in length. The greatest distance between the relay batteries of the French line will be a little over a thousand. These distances, with wires properly insulated, are held to be within effective telegraphic reach.
60. Faulty cables.—One of the chief physical difficulties which seem now to stand in the way of these lines lies with the "cables." It so happens that all deep-sea lines have at the present writing ceased to work. The two Malta lines in the Mediterranean are out of order; so also are the Red Sea lines: no messages have passed between Kurrachee and Aden for some time, and the line to Algiers has been suspended, if not abandoned, for the present.
61. Their iron wrappings.— All these lines had cables encased in a wrapping of iron wire;—and it is a question whether the difficulty with them all be not owing to that circumstance. The wire wrapping of the Atlantic cable has been found in a state almost of complete disintegration, like the iron fastenings of coppered ships. This evidence of galvanic action excites suspicions as to the proper insulation of that cable. Iron, sea-water, and copper, will make a battery of no inconsiderable power; and the decayed state of the iron wire in this instance encourages the belief as to defective insulation.
62. Imperfect insulation.—Such are the facts. But the facts do not prove that gutta-percha is an imperfect insulator. With regard to the Atlantic cable, they suggest that the insulation of that cable, though perfect at first, might have been injured by the handling to which the cable was afterwards subjected, and above all by the heavy strains which were brought upon it by the "brakes" during the operation of laying it along the plateau.
63. The Red Sea and Mediterranean cables.—These facts, however, do not suggest the same for the Red Sea and Mediterranean cables, for these cables had all been down for some time, and had been working more or less satisfactorily; nevertheless, we are reminded by these failures now, and that too from a fresh quarter, that iron wrappings about a telegraphic wire are of no use in the deep sea.[7]
64. A galvanic battery in the sea.—Two metals, as a copper conductor and an iron wrapper, would seem not to be desirable for the same cord, for in case of leakage a galvanic battery is at once formed in the sea, and brought into play upon the cable. not only so, the cable itself is a long and powerful Leyden jar; the iron wrapping assists to make it so. This circumstance may also assist to excite the two metals still more, and so hasten the destruction of the cable as an electrical conductor.
65. Two metals should not be used about a submarine cable.—But independent of these facts and views, there is another reason why iron wrappings and two metals should not he used, at least for deep-sea cables. Our researches at sea have shown that there is no running water at the bottom of the deep sea. Hence we infer that a telegraphic cord once lodged on the bottom of the ocean, there, as the tree that falls in the forest, it would lie; for there is nothing to disturb it more. Wherefore it has been held,[8] that the iron wrapping for deep-sea lines of telegraph, instead of being advantageous in any aspect, are not only a hindrance, but an incumbrance also and a waste: the weight of the cord may be adjusted to sinking by the size of the conducting wire within as well as by the character of the non-metallic wrapping without.
66. Rogers's cable "jacket."—Whether the insulating material be gutta-percha, india-rubber, or other matter, it requires to be protected from chafes and bruises while on board, and when it is being payed out. And it may be so protected by a covering, not of wire, but of silk, hemp, flax, or cotton. An ingenious American[9] has invented a "jacket," which will not only protect the cable while on board, but afterwards also, and when it is at the bottom even in shallow and running water. Thus one of the obstacles which have been interfering with the progress of submarine telegraphy is removed out of the way.
67. Deep-sea temperatures a desideratum.—But notwithstanding all that has been done with the sea and in the sea for the electro-magnetic telegraph, and for human progress, there still remain many agenda. There is both room and need for further research, more exploration, and many experiments. As bearing upon the best insulating material for submarine lines of telegraph, a good series of deep-sea temperatures is much needed. Of all those who are now engaged in observing and studying with us, and for us, the phenomena of the sea, are there none who will make deep-sea temperatures a speciality? They would no doubt prove as instructive and as useful too as deep-sea soundings have been and are. 68. Specimens from the depth of 19,800 feet.—Lieutenant Brooke, in the "Hancock," has obtained soundings in the North Pacific from the depth of 3300 fathoms, with specimens both of the ooze and the water at the bottom. These have been sent to Professor Ehrenberg of Berlin, for microscopic examination. He has not completed his study of these treasures, but he already reports the discovery in them of more than one hundred new species of animalculæ.
- ↑ Those of Mr. Welsh, in his ascent from Kew.
- ↑ "And be it further enacted. That the Secretary of the Navy be directed to detail three suitable vessels of the navy in testing new routes and perfecting the discoveries made by Lieut. Maury in the course of his investigations of the winds and currents of the ocean; and to cause the vessels of the navy to cooperate in procuring materials for such investigations, in so far as said co-operation may not be incompatible with the public interests."-From Naval Appropriation Bill, approved March 3, 1849.
- ↑ Encyclop. Metropol.
- ↑ Notes of a Russian Officer, p. 97, No. 2 (Feb. 1856), vol. xxv., Nautlcal Magazine, London.
- ↑ Ex. Doc. No. 22, Senate, 1st sess. 34th Congress, p. 342.
- ↑ Maury's Sailing Directions, vol. i. Sir John Herschel quotes it at 1.0275 for 62°.
- ↑ "Therefore it may now be considered a settled principle in submarine telegraphy, that the true character of a cable for the deep sea is not that of an iron rope as large as a man's arm, but of a single copper wire, or a fascicle of wire, coated with gutta-percha, pliant and supple, and not larger than a lady's finger."—[M.F. Maury's] Letter to Secretary of the Navy, November 8, 1850.
- ↑ Vide Letter to Secretary of the Navy, November 8, 1856. Maury's Sailing Directions, chapter Submarine Telegraphy; ditto, Physical Geography of the Sea, chapters XIII. and XXI. Harper Brothers, New York, 1859; also Journal Royal Dublin Society, numbers XII. and XIII. Letter to John Locke, on the Atlantic Telegraph causes of failure and probabilities of ultimate success. Read January, 1859.
- ↑ Henry J. Rogers of Baltimore