Physical Geography of the Sea and its Meteorology/Chapter 13
CHAPTER XIII.
§ 560-575.—THE DEPTHS OF THE OCEAN.
560. Submarine scenery.—"We dive," says Schleiden,[1] "into the liquid crystal of the Indian Ocean, and it opens to us the most wondrous enchantments, reminding us of fairy tales in childhood's dreams. The strangely branching thickets bear living flowers. Dense masses of meandrinas and astræas contrast with the leafy, cup-shaped expansions of the explanaries,'the variously-ramified Madrepores, which are now spread out like fingers, now rise in trunk-like branches, and now display the most elegant array of interlacing branches. The colouring surpasses everything; vivid green alternates with brown or yellow; rich tints of purple, from pale red-brown to the deepest blue. Brilliant rosy, yellow, or peach-coloured Nullipores overgrow the decaying masses, and are themselves interwoven with the pearl-coloured plates of the Retipores, resembling the most delicate ivory carvings. Close by wave the yellow and lilac fans, perforated like trellis-work, of the Gorgonias. The clear sand of the bottom is covered with the thousand strange forms and tints of the sea-urchins and star- fishes. The leaf-like flustras and escharas adhere like mosses and lichens to the branches of the corals; the yellow, green, and purple-striped limpets cling like monstrous cochineal insects upon their trunks. Like gigantic cactus-blossoms, sparkling in the most ardent colours, the sea-anemones expand their crowns of tentacles upon the broken rocks, or more modestly embellish the flat bottom, looking like beds of variegated ranunculuses. Around the blossoms of the coral shrubs play the humming-birds of the ocean, little fish sparkling with red or blue metallic glitter, or gleaming in golden green, or in the brightest silvery lustre. Softly, like spirits of the deep, the delicate milk-white or bluish bells of the jelly-fishes float through this charmed world. Here the gleaming violet and gold-green Isabelle, and the flaming yellow, black, and vermilion-striped coquette, chase their prey; there the band-fish shoots, snake-like, through the thicket, like a long silver ribbon, glittering with rosy and azure hues. Then come the fabulous cuttle-fishes, decked in all the colours of the rainbow, but marked by no definite outline, appearing and disappearing, intercrossing, joining company and parting again, in most fantastic ways; and all this in the most rapid change, and amid the most wonderful play of light and shade altered by every breath of wind, and every slight curling of the surface of the ocean. When day declines, and the shades of night lay hold upon the deep, this fantastic garden is lighted lip in new splendour. Millions of glowing sparks, little microscopic medusas and crustaceans, dance like glow-worms through the gloom. The sea-feather, which by daylight is vermilion-coloured, waves in a greenish, phosphorescent light. Every corner of it is lustrous. Parts which by day were perhaps dull and brown, and retreated from the sight amid the universal brilliancy of colour, are now radiant in the most wonderful play of green, yellow, and red light; and, to complete the wonders of the enchanted night, the silver disk, six feet across, of the moon fish,[2] moves, slightly luminous, among the cloud of little sparkling stars. The most luxuriant vegetation of a tropical landscape cannot unfold as great wealth of form, while in the variety and splendour of colour it would stand far behind this garden landscape, which is strangely composed exclusively of animals, and not of plants; for, characteristic as the luxuriant development of vegetation of the temperate zones is of the sea bottom, the fullness and multiplicity of the marine Fauna is just as prominent in the regions of the tropics. Whatever is beautiful, wondrous, or uncommon in the great classes of fish and Echinoderms, jelly-fishes and Polypes, and the Mollusks of all kinds, is crowded into the warm and crystal waters of the tropical ocean—rests in the white sands, clothes the rough cliffs, clings, where the room is already occupied, like a parasite, upon the first comers, or swims through the shallows and depths of the elements—while the mass of the vegetation is of a far inferior magnitude. It is peculiar in relation to this that the law valid on land, according to which the animal kingdom, being better adapted to accommodate itself to outward circumstances, has a greater diffusion than the vegetable kingdom—for the polar seas swarm with whales, seals, sea-birds, fishes, and countless numbers of the lower animals, even where every trace of vegetation has long vanished in the eternally frozen ice, and the cooled sea fosters no sea-weed—that this law, I say, holds good also for the sea, in the direction of its depth ; for when we descend, vegetable life vanishes much sooner than the animal, and, even from the depths to which no ray of light is capable of penetrating, the sounding-lead brings up news at least of living infusoria."—Schleiden's Lectures, p. 403—406.
561. Ignorance concerning the depth of "blue water"—Until the commencement of the plan of deep-sea soundings, as they have been conducted in the American and English navies, the bottom of what the sailors call "blue water" was as unknown to us as is the interior of any of the planets of our system. Ross and Dupetit Thouars, with other officers of the English, French, and Dutch navies, had attempted to fathom the deep sea, some with silk threads, some with spun-yarn (coarse hemp threads twisted together), and some with the common lead and line of navigation. All of these attempts were made upon the supposition that when the lead reached the bottom, either a shock would be felt, or the line, becoming slack, would cease to run out.
562. Early attempts at deep-sea soundings—unworthy of reliance.—The series of systematic experiments recently made upon this subject show that there is no reliance to be placed on such a supposition, for the shock caused by striking bottom cannot be communicated through very great depths. Furthermore, the lights of experience show that, as a general rule, the under currents of the deep sea have force enough to take the line out long after the plummet has ceased to do so. Consequently, there is but little reliance to be placed upon deep-sea soundings of former methods, when the depths reported exceeded eight or ten thousand feet.
563. Various methods tried or proposed.—Attempts to fathom the ocean, both by sound and pressure, had been made, but out in "blue water" every trial was only "a failure repeated. The most ingenious and beautiful contrivances for deep-sea soundings were resorted to. By exploding petards, or ringing bells in the deep sea, when the winds were hushed, and all was still, the echo or reverberation from the bottom might, it was held, be heard, and the depth determined from the rate at which sound travels through water. But, though the concussion took place many feet below the surface, echo was silent, and no answer was received from the bottom. Ericsson and others constructed deep-sea leads having a column of air in them, which, by compression, would show the aqueous pressure to which they might be subjected. This was found to answer well for ordinary purposes, but in the depths of the sea, where the pressure would be equal to several hundred atmospheres, the trial was more than this instrument could stand. Mr. Baur, an ingenious mechanician of New York, constructed, according to a plan which I furnished him, a deep-sea sounding apparatus. To the lead was attached, upon the principle of the screw propeller, a small piece of clockwork for registering the number of revolutions made by the little screw during the descent, and it having been ascertained by experiment in shoal water that the apparatus, in descending, would cause the propeller to make one revolution for every fathom of perpendicular descent, hands provided with the power of self-registration were attached to a dial, and the instrument was complete. It worked beautifully in moderate depths, but failed in blue water, from the difficulty of hauling it up if the line used were small, and from the difficulty of getting it down if the line used were large enough to give the requisite strength for hauling it up. An old sea-captain proposed a torpedo, such as is sometimes used in the whale fishery for blowing up the monsters of the deep, only this one was intended to explode on touching the bottom. It was proposed first to ascertain by actual experiment the rate at which the torpedo would sink, and the rate at which the sound or the gas would ascend, and so, by timing the interval, to determine the depth. This plan would afford no specimens of the bottom, and its adoption was opposed by other obstacles. One gentleman proposed to use the magnetic telegraph. The wire properly coated, was to be laid up in the sounding-line, and to the plummet was attached machinery, so contrived that on the increase of every 100 fathoms, and by means of the additional pressure the circuit would be restored, somewhat after the manner of Dr. Locke's electro-chronograph, and a message would come up to tell how many hundred fathoms up and down the plummet had sunk. As beautiful as this idea was, it was not simple enough in practical application to answer our purposes.
564. Physical problems more difficult than that of measuring the depth of the sea have been accomplished.—Greater difficulties than any presented by the problem of deep-sea soundings had been overcome in other departments of physical research. These plans and attempts served to encourage, nor were they fruitless, though they proved barren of practical results. Astronomers had measured the volumes and weighed the masses of the most distant planets, and increased thereby the stock of human knowledge. Was it creditable to the age that the depths of the sea should remain in the category of an unsolved problem? Its "ooze and bottom" was a sealed volume, rich with ancient and eloquent legends, and suggestive of many an instructive lesson that might be useful and profitable to man. The seal which covered it was of rolling waves many thousand feet in thickness. Could it not be broken? Curiosity had always been great, jet neither the enterprise nor the ingenuity of man had as yet proved itself equal to the task. No one had succeeded in penetrating and bringing up from beyond the depth of two or three hundred fathoms below the aqueous covering of the earth any solid specimens of solid matter for the study of philosophers.
565. The deep-sea sounding apparatus of Peter the Great.—The honour of the first attempt to recover specimens of the bottom from great depths belongs to Peter the Great of Russia. That remarkable man and illustrious monarch constructed a deep-sea sounding apparatus especially for the Caspian Sea. It was somewhat in the shape of a pair of ice-hooks, and such as are seen in the hands of the "ice-man," as, in his daily rounds, he lifts the blocks of ice from his cart in the street for delivery at the door. It was so contrived that when it touched the bottom the met would become detached, and the hook would bring up the specimen.
566. A plan of deep-sea sounding devised for the American navy.—The sea, with its myths, has suggested attractive themes to all people in all ages. Like the heavens, it affords an almost endless variety of subjects for pleasing and profitable contemplation, and there has remained in the human mind a longing to learn more of its wonders and to understand its mysteries. The Bible often alludes to them. Are they past finding out? How deep is it? and what is at the bottom of it? Could not the ingenuity and appliances of the age throw some light upon these questions? The government was liberal and enlightened; times seemed propitious; but when or how to begin, after all these failures, with this interesting problem, was one of the difficulties first to be overcome. It was a common opinion, derived chiefly from a supposed physical relation, that the depths of the sea are about equal to the heights of the mountains. But this conjecture was, at best, only a speculation. Though plausible, it did not satisfy. There were, in the depths of the sea, untold wonders and inexplicable mysteries. Therefore the contemplative mariner, as in mid-ocean he looked down upon its gentle bosom, continued to experience sentiments akin to those which fill the mind of the devout astronomer when, in the stillness of the night, he looks out upon the stars, and wonders. Nevertheless, the depths of the sea still remained as fathomless and as mysterious as the firmament above. Indeed, telescopes of huge proportions and of vast space-penetrating powers had been erected here and there by the munificence of individuals, and attempts made with them to gauge the heavens and sound out the regions of space. Could it be more difficult to sound out the sea than to gauge the blue ether and fathom the vaults of the sky? The result of the astronomical undertakings[3] lies in the discovery that what, through other instruments of less power, appeared as clusters of stars, were, by these of larger powers, separated into groups, and what had been reported as nebulae, could now be resolved into clusters; that in certain directions, the abyss beyond these faint objects is decked with other nebulæ, which these great instruments may bring to light but cannot resolve; and that there are still regions and realms beyond which the rays of the brightest sun in the sky have neither the intensity nor the force to reach, much less to penetrate. And what is more, these monster instruments have revealed to us, in those distant regions, forms or aggregations of matter which suggest to some the idea of the existence of physical forces there that we do not understand, and which raise the question in speculative minds, Is gravitation a universal thing, and do its forces penetrate every abyss of space? Could we not gauge the sea as well as the sky and devise an instrument for penetrating the depths of the ocean as well as the depths of space? Mariners were curious concerning the bottom of the sea. Though nothing thence had been brought to light, exploration had invested the subject with additional interest, and increased the desire to know more. In this state of the case, the idea of a common twine thread for a sounding-line, and a cannon ball for a sinker, was suggested. It was a beautiful conception; for, besides its simplicity, it had in its favour the greatest of recommendations, it could be readily put into practice.
567. The great depths and failures of the first attempts.—Well-directed attempts to fathom the ocean began now to be made with such a line and plummet, and the public mind was astonished at the vast depths that were at first reported. Lieutenant Walsh, of the United States schooner "Taney," reported a cast with the deep-sea lead at thirty-four thousand feet without bottom. His sounding-line was an iron wire more than eleven miles in length. Lieutenant Berryman, of the United States brig "Dolphin," reported another unsuccessful attempt to fathom mid-ocean with a line thirty-nine thousand feet in length. Captain Denham, of Her Britannic Majesty's ship "Herald," reported bottom in the South Atlantic at the depth of forty-six thousand feet; and Lieutenant J. P. Parker, of the United States frigate "Congress," afterwards, in attempting to sound near the same region, let go his plummet, and saw it run out a line fifty thousand feet long as though the bottom had not been reached. There are no such depths as these. The three last-named attempts were made with the sounding-twine of the American navy, which has been introduced in conformity with a very simple plan for sounding out the depths of the ocean. It involved for each cast only the expenditure of a cannon ball, and twine enough to reach the bottom. This plan was introduced as a part of the researches conducted at the National Observatory, and which have proved so fruitful and beneficial, concerning the winds and currents and other phenomena of the ocean. These researches had already received the approbation of the Congress of the United States; for that body, in a spirit worthy of the representatives of a free and enlightened people, had authorized the Secretary of the Navy to employ three public vessels to assist in perfecting the discoveries, and in conducting the investigations connected therewith.
668. The plan finally adopted.—The plan of deep-sea soundings finally adopted, and now in practice, is this: Every vessel of the navy, when she puts to sea, is, if she desires it, furnished with a sufficient quantity of sounding-twine, carefully marked at every length of one hundred fathoms—six hundred feet—and wound on reels of ten thousand fathoms each. It is made the duty of the commander to avail himself of every favourable opportunity to try the depth of the ocean, whenever he may find himself out upon "blue water," For this purpose he is to use a cannon-ball of 32 or 68 pounds as a plummet. Having one end of the twine attached to it, the cannon-ball is to be thrown overboard from a boat or a steamer, and suffered to take the twine from the reel as fast as it will. The reel is made to turn easily A silk thread, or the common wrapping-twine of the shops, would, it was thought, be strong enough for this purpose, for it was supposed there would be no strain upon the line except the very slight one required to drag it down, and the twine having nearly the specific gravity of sea water, this strain would, it was imagined, be very slight. Moreover, when the shot reached the bottom, the line, it was thought (§ 561), would cease to run out; then breaking it off, and seeing how much remained upon the reel, the depth of the sea could be ascertained at any place and time simply at the expense of one cannon-ball and a few pounds of common twine.
669. Discovery of currents in the depths of the sea.—But practical difficulties that were not expected at all were lurking in the way, and afterwards showed themselves at every attempt to sound; and it was before these practical difficulties had been fairly overcome that the great soundings (§ 667) were reported. In the first place, it was discovered that the line, once started and dragged down into the depths of the ocean, never would cease to run out (§ 662), and, consequently, that there was no means of knowing when, if ever, the shot had reached the bottom. And, in the next place, it was ascertained that the ordinary twine (§ 666) would not do; that the sounding-line, in going down, was really subjected to quite a heavy strain, and that, consequently, the twine to be used must be strong; it was therefore subjected to a test which required it to bear a weight of at least sixty pounds freely suspended in the air. So we had to go to work anew, and make several hundred thousand fathoms of sounding-twine especially for the purpose. It was small, and stood the test required, a pound of it measuring about six hundred feet in length. The officers intrusted with the duty soon found that the soundings could not be made from sailing vessels with any certainty as to the depth. It was necessary that a boat should be lowered, and the trial be made from, it; the men with their oars keeping the boat from drifting, and maintaining it in such a position that the line should be "up and down "the while. That the line would continue to run out after the cannon-ball had reached bottom, was explained by the conjecture that there is in the ocean, as in the air, a system of currents and counter currents one above the other, and that it was one or more of these submarine currents, operating upon the bight of the line, which caused it to continue to run out after the shot had reached the bottom. In corroboration of this conjecture, it was urged, with a truth-like force of argument, that it was these under currents, operating with a "swigging" force upon the bights of the line—for there might be several currents running in different directions, and operating upon it at the same time—which caused it to part whenever the reel was stopped and the line held fast in the boat.
570. Evidence in favour of a regular system of oceanic circulation.—A powerful train of circumstantial evidence was this (and it was derived from a source wholly unexpected), going to prove the existence of that system of oceanic circulation which the climates, and the offices, and the adaptations of the sea require, and which its inhabitants (§ 465) in their mute way tell us of. This system of circulation commenced on the third day of creation, with the "gathering together of the waters," which were "called seas;" it will probably continue as long as sea water shall possess the properties of saltness and fluidity.
571. Method of making a deep-sea sounding.—In making these deep-sea soundings, the practice is to time the hundred fathom marks (§ 568) as they successively go out; and by always using a line of the same size and "make," and a sinker of the same shape and weight, we at last established the law of descent. Thus the mean of our experiments gave us, for the sinker and twine used,
| 2 m. 21 s. | as the | average time | of descent from | 400 to 500 | fathoms. |
| ,, | ,, | ,, | ,, | 1000 to 1100 | ,, |
| 4 m. 29 s. | ,, | ,, | ,, | 1800 to 1900 | ,, |
572. The law of the plummets descent.—Now, by aid of the law here indicated, we could tell very nearly when the ball ceased to carry the line out, and when, of course, it began to go out in obedience to the current and drift alone; for currents would sweep the line out at a uniform rate, while the cannonball would drag it out at a decreasing rate. The development of this law was certainly an achievement, for it enabled us to show that the depth of the sea at the places named (§ 567) was not as great as reports made it. These researches were interesting: the problem in hand was important, and it deserved every effort that ingenuity could suggest for reducing it to a satisfactory solution.
573. Brooke's sounding apparatus.—As yet no specimens of the bottom had been brought up. The line was too small, the shot was too heavy, and it could not be weighed; and if we could reach the bottom, why should w^e not know its character? In this state of the case. Passed Midshipman J. M. Brooke, United States Navy, who at the time was associated with me on duty at the Observatory, proposed a contrivance by which the shot, on striking the bottom, would detach itself from the line, and send up a specimen of the bottom. This beautiful contrivance, called Brooke's Deep-sea Sounding Apparatus, is represented on p. 313. A is a cannon-ball, having a hole through it for the rod B. Figure 1 represents the rod B, and the slings D D, with the shot slung, ready for sounding. Figure 2 represents the apparatus in the act of striking the bottom; it shows how the shot is detached, and how specimens of the bottom are brought up, by adhering to a little soap or tallow,[4] called "arming," in the cup C, at the lower end of the rod B. With this contrivance specimens of the bottom have been brought up from the depth of nearly four miles.
574. The deepest part of the Atlantic Ocean.—The greatest depths at which the bottom of the sea has been reached with the plummet are in the North Atlantic Ocean, and the places where it has been fathomed do not show it to be deeper than twenty-five thousand feet. The deepest place in this ocean (Plate XI.) is probably between the parallels of 35° and 40° north latitude, and immediately to the southward of the Grand Banks of Newfoundland. The first specimens have been received from the coral sea of the Indian Archipelago and from the North Pacific. They were collected by the surveying expedition employed in those seas. A few soundings have been made in the South Atlantic, but not enough to justify deduction as to its depths or the precise shape of its floor.
575. Deep-sea soundings by the English navy.—The friends of physical research at sea are under obligations to the officers of the English navy for much valuable information touching this interesting subject. Certain officers in that service have taken up the problem of deep-sea soundings with the most praise-worthy zeal, energy, and intelligence. Dayman in the Atlantic, Captains Spratt and Mansell in the Mediterranean, with Captain Pullen in the Red Sea, have all made valuable contributions to the stock of human knowledge concerning the depths and bottom of the sea. To Mansell and Spratt we are indebted for all we know about deep-sea soundings in the Mediterranean, as we are to Pullen for those in the Red Sea. By their lines of soundings, their maps and profiles, they have enabled physical geographers to form, with some approach towards correctness, an idea as to the orography of the basins which hold the water for these two seas. We are also indebted to the French for deep-sea soundings in the Mediteranean. That sea appears to be about two miles deep in the deepest parts, which are in the isleless spaces to the west of Sardinia and to the east of Malta.