Transactions of the Asiatic Society of Japan/Series 1/Volume 2/Concerning Deep Sea Sounding
CONCERNING DEEP SEA SOUNDING.
BY
Captain BELKNAP, U.S.N.
Read before the Asiatic Society of Japan,
on the 13th May, 1874.
——o——
The accurate determination of the depth of the sea is a problem which has long puzzled the minds of seamen and scientists, but which now seems in a fair way of satisfactory solution.
The activity of scientific research in all branches of investigation, and the needs of commerce at the present day, demanding quick intercourse between remote parts of the world by means of telegraphic communication through submarine cables, have stimulated effort in the direction of Deep Sea Sounding, and finally made easy and indisputable a work which had hitherto been difficult and unreliable.
We hear no longer of almost bottomless depths in the Ocean; of pressures so great that nothing, whether of wood or iron, could sink below their plane; of an utter absence of life on the Ocean bed; or of a uniform temperature of 39° F., which was believed to exist after reaching down to a certain point beneath the surface. All these ideas have been exploded by the invention of the needed appliances, and the results of Deep Sea work during the past twenty years.
Under old methods with ordinary sinkers and heavy hempen lines, it was found exceedingly difficult to tell when the lead reached bottom in depths beyond 1,200 fathoms, the friction and weight increasing to such a degree that the touch of the plummet could not be felt sensibly enough to make the fact sure; and the line would continue to run out indefinitely simply, from its own weight.
For many years, distinguished officers in the principal Naval services, strove in vain to solve the problem. Spun-yarn, silken lines, fishing lines and wire were tried, but generally, with little or no success.
Captain Denham, of H. M. S. Herald, thought he found bottom, sounding in the South Atlantic, at a depth of 46,000 feet. Lieut. Parker of the U. S. S. Congress, sounding off the coast of Brazil, ran out 50,000 feet of line, reporting no bottom at that great depth, (some 9 miles). Lieut. Walsh, U. S. N. sounded with 34,000 feet of wire without feeling bottom, and Lieut. Berryman, in the U. S. brig Dolphin, ran out a line of 39,000 feet with no more definite results.
We know now that all those soundings were defective, and that hardly more than half or two-thirds of those depths exist anywhere in the Ocean. The deepest reliable sounding yet on record was recently made by H. M. S. Challenger, between St. Thomas and Bermuda, where a depth of 23,250 feet was found.
One trouble with the small lines was that they were not strong enough to bring the sinker back to the surface, but would generally break from the strain imposed upon them at great depths; another trouble arose from the fact that the line was let run as fast as it would go out, and, in fact, was rather assisted than retarded, so that the shock of striking, communicated through the dense mass of water by the line, was not felt perceptibly enough to make the fact unquestionable, and, in short, the moment of touch was never known, but guessed at, more or less.
Again, it was almost impossible to keep a sailing vesssel directly over the line, and the drift of the ship and action of currents upon the rope, gave very imperfect results, even at depths of no more than 1,000 fathoms, and where the indications were good that bottom had been reached.
In surveying the immense coast line of the United States, the U.S. Coast Survey, then under the direction of Prof. Bache, undoubtedly initiated the first systematic endeavour to grapple with this important problem; and Lieut. Maury, of the National Observatory, seizing the opportunity, proposed that strong twine, made expressly for the purpose, should be used with 32 lb. and 68 lb. shot for sinkers, and, instead of sounding from the ship, he suggested the work should be done from a boat; the idea being that the boat could be kept directly over the line by means of the oars, and the twine being so small and light in proportion to the weight of the sinker, the shock of striking might be felt as it ran through the hand the twine to be cut when bottom was reached, without trying to haul it back; thus a proportionately heavier sinker could be used than with the methods previously in vogue.
The U. S. brig Dolphin, under the command of Lieutenant, now Rear-Admiral, S. P. Lee, U.S.N., was the first to try that experiment, and after a number of failures which tested the patience and skill of that officer to the utmost, he finally succeeded, and the results obtained by that vessel were probably the most reliable which had been obtained up to that time. But this success lacked one important feature; specimens of the bottom were needed, not only to put beyond doubt the accuracy of the sounding, but to bring to the light of investigation the character of the soil from the ocean bed.
Then it was that, Lieutenant J. M. Brooke, U.S.N., invented the simple and beautiful contrivance of detaching the sinker and dropping it on the bottom, leaving a small rod, hollowed out at the bottom, in which were fixed open quills, to be hawed back on board by the twine. In the act of striking, the quills would fill with mud, and retain it till drawn up to the surface.
Lieutenant, now Rear-Admiral, B. F. Sands, U.S.N., also devised an apparatus by which a split sinker was made to fall apart when it touched bottom, leaving a cup, ingeniously arranged to bring up specimens of the bottom, but the Brooke apparatus seemed to find the most favour, and from that time forward, 1854, that apparatus, or modifications of it, or machines based upon the principle of getting rid of the sinker, have been used in all services making deep sea explorations. On this head Prof. Austed, in his “Geological Gossip” says, “We have to thank our brethren from the other side of the Atlantic for a number of trials and experiments, with various modifications of the old sounding-line, and also for the introduction of a simple and efficacious contrivance for overcoming the difficulty. Brooke’s sounding apparatus, slightly modified in matter of detail, is now generally employed, with the greatest success, to obtain proofs not only of the depth, but of the nature of the bottom of ocean.” In the English service the “Bull-dog,” the “Fitzgerald,” and “Hydra” machines, have been mostly used, the latter being the favourite, and which is now in use on board H. M. S. Challenger.
It was about this time too, that Mr. Massey, an English inventor, devised his sounding machine, which was a contrivance of cogwheels turned by the action of the water on a screw.
The machine was attached to the line above the lead, and in descending, the revolutions of the screw gave motion to the cogwheels, which registered the number of fathoms corresponding to the number of fathoms reached. This machine was a good step in advance, but owing to the enormous pressure of the water at great depths, which seemed to effect the perfect working of the wheels, the results were not so reliable as at first glance would appear.
These inventions happened just at the “nick of time,” for the first Atlantic cable was then in contemplation, and the U. S. steamer Active, the first steamer used in making deep-sea soundings, was fitted out with every appliance, including a steam-reel, which experience suggested up to that time, and was placed under the command of Lieut. O. H. Berryman for the purpose of sounding out a route for the proposed cable. The line was run, both the Brooke and Massey apparatus being used, and many good specimens of bottom soil were brought up, but Lieutenant Maury, questioning the accuracy of some of the Active’s work, the English Admiralty sent H. M. steamer Cyclops, Lieut. Dayman, to go over the same ground. Lieut. Dayman used Brooke’s apparatus, slightly modified, and the soundings made by him substantially verified those made by Berryman.
In 1858, Brooke, in the U. S. brig Dolphin tested his own apparatus in sounding in various parts of the North Pacific, and in 1868, Captain Shortland, R.N., in H. M. S. Hydra, ran a line of soundings from Bombay to Aden for cable purposes. On board that vessel was devised the Hydra machine, in which a spring was substituted for the trigger in the Brooke apparatus, and the tube for specimens was fitted with a piston and a series of valves. This machine, as before mentioned, is the one now prefered in the English service, and in use on board the Challenger. Captain Shortland kept a certain amount of tension on the line, and noted the time each hundred fathoms took in running out, then watching closely when the sinker was supposed to reach bottom,—the line was still permitted to run on, and if with diminished speed, it was considered that bottom had been reached: of course, if the specimen tube came up alone, leaving the sinker on the bottom, there could be little doubt of the value of the sounding. In 1870 and 1871, Commander Jno. Irwin, in the U.S.S. Yantic sounded among the West India Islands and in the Carribbean Sea. He used Massey’s apparatus and undetachable lead, with specimen cup invented by Rear Admiral Sands, and sometimes duplicated the soundings in order to verify results.
The very successful sounding and dredging expeditions of H. M. Ships Lightning and Porcupine in 1868, 1869 and 1870 under the scientific direction of Dr. Carpenter and Professor Wyville Thomson, led the English Admiralty to fit out the Challenger for the cruise upon which she is now engaged. She has a large scientific corps on board with Professor Wyville Thomson at its head, and I believe may be expected to arrive in the waters of Japan sometime in 1875.
The Tuscarora was fitted out at the Navy Yard, Mare Island, Cal., in the summer of 1873, for the purpose of sounding between the shores of the U.S. and Japan, to ascertain the practicability of a cable route across the North Pacific. She was originally fitted with two machines; one, a heavy dynamometer, devised by Passed Assistant Engineer T. W. Rae, U. S. Navy, for sounding with a rope or cord; and the other, a small reel and dynamometer, invented by Sir William Thomson, of Glasgow University, to be used with fine piano wire.
The heavy dynamometer worked well at depths of 1,800 fathoms, beyond which it was not tried, as, owing to the sudden complications with Spain it was taken out of the ship to make room for a gun. Had that machine been kept on board, it was further intended to use with it a small cord, or rope of wire, instead of the hempen line, and the results would undoubtedly have been good. When sounding with that machine, the line passed from the reel with two or three turns round a large drum twelve feet in circumference,—the revolutions being registered by a counter, so that the length of line out was indicated both by the counter and the marks on the line. The principle upon which the working of the machine was based, was essentially the same as that which constitutes the chief merit of the Thomson dynamometer; but this machine being out of the question for the cause above given, the Thomson machine had it all its own way, and so admirable has been its working, and so accurate are its indications that, it seems to be no more than due the genius of Sir William to say, that the appliances for what may be, not inaptly called, the perfection of Deep Sea Sounding, originated with him. Wire had been tried by Lieut. Walsh on board the U. S. schooner Taney, so far back as 1849, but the happy thought had not occurred to him to measure the weight of the wire as it ran out, and applying a counterbalancing weight inside to restrain it in its descent, hence the specific gravity of the wire being so great, it would continue to run on forever, if permitted, without giving any indication of touching bottom and so its use was abandoned.
The Thomson machine consists of a reel or drum six feet in circumference, made of galvanized sheet iron. The drum is about four inches in width and has a rim on each side from one and a half inches to two inches in height. Around the right side of the drum runs a V groove which takes the endless rope or pulley line which controls the revolutions of the drum in sounding.
The drum weighs about 60 lbs., and will readily hold five miles of the piano wire. It rests on a light iron frame bolted to a wooden bed and can be readily unshipped when not required for use. Close behind the rim of the drum, and directly in line with the V groove, is fixed a light iron wheel ten inches in diameter; this wheel, called the dynamometer wheel, has one groove wide enough to hold two parts of line, and a second narrow groove to receive a cord simply. Back of this wheel is a common spring balance, which will register a strain of 110 lbs.
Some twenty-five feet from the reel is fixed a pully wheel, connected with the drum on one side, by the endless rope, and having a pendant on its other side running through a block suspended for the purpose. To the pendant are attached hooks from which to suspend weights of different sizes. The inventor used a tackle, instead of a pendant and weight, to be hauled taut as occasion required; but weights were substituted as being easier to manage and more satisfactory in their working, as by that means a steady, known and invariable strain could be had as desired, according as the weight of wire and sinker out, make increased power on the pulley necessary.
In getting the machine ready to sound, an endless rope of medium size is fitted into the grooves of the drum and pulley wheel, like an ordinary belt; then a full turn is taken round the dynamometer wheel, the latter being secured to the spring balance by a small cord resting in the narrow groove, and passing down through a small hole in the wheel; weights then being hooked to the pendant, the endless rope tautens, and the machine is ready for use.
When the machine is in operation, the pulley line, or endless rope, runs freely round with the drum and pulley wheel, but the dynamometer wheel being held fast by the small cord attached to the spring balance, the friction of the turns of the rope running round the wheel expends itself in bringing a strain on the balance, the index of which registers the number of pounds of that strain; it is needless to say the strain is in proportion to the amount of weight on the pendant.
The piano wire No. 22 in size, weighs, in water, about 12 lbs. to the statute mile, and will bear a strain of from 200 lbs to 230 lbs. The wire comes in lengths of from 200 fathoms to about 400 fathoms, and has to be spliced to make it available for sounding purposes. The splices are made some three feet in length, the parts being put together with a long jawed twist, and the ends and three or four intermediate points secured with solder. The whole length of the splice is then served with fine waxed thread and the splice is complete. In no case have the splices drawn or broken. To keep the wire free from rust, it is kept at all times when not in immediate use, in tank containing a solution of caustic soda. This protects the wire completely, and the piece before the Society this evening has been in use ten months.
To the outer end of the wire is attached a light galvanized iron ring, or rope grummet, to which is made fast some 25 fathoms of cord or Albacore line; to the other end of this line is attached the apparatus for the detachable sinker and specimen cup. The purpose of this line is to prevent the wire from coming into contact with the bottom, for if that were allowed, the wire being stiff and elastic, would be apt to fly upward, kink, and break.
The sinkers used are 8-inch shot with holes bored through their centres 214 inches, and 234 inches in diameter, through which the Brooke detaching rod and the specimen cylinders are passed; their weight is 55 lbs. and 51 lbs. Sir William Thomson used a lead sinker weighing 30 lbs. which he hauled back with the wire, but that plan put too much stress on the machine in reeling in, and the heavier sinker to be detached by Brooke’s apparatus was adopted on board the Tuscarora. Sir William has now abandoned the hauling back of the sinker, I believe.
The cups or cylinders, of three different designs, used on board the Tuscarora with the Brooke apparatus, were devised on board, and work so well that mud enough to fill a five ounce vial is sometimes brought up.
The soundings are taken from the gangway, as being nearer the centre of motion than any other convenient part of the ship, and therefore less subjected to the pitching and yawing motion of the vessel.
When it is required to sound, supposing the ship to be under sail, the fires, which have been banked, are spread, and when steam is ready, say in half an hour, the usual time, all sails are furled, and kept in that position by the backing of the engines. In calm or light weather, the use of the engines is only required at intervals, at other times, when the wind is fresh and the sea heavy, they are kept backing all the time, and sometimes at full speed.
Meanwhile the machine has been got ready, and when the ship has lost headway and become steady, so that the wire can run straight down, the sinker is carefully lowered into the water by hand. Then the self-registering thermometer for ascertaing the bottom temperature is attached to the cod-line, and the line is allowed to run out gently until the wire is reached, when the latter is clamped to prevent further egress until a leaden weight of some four pounds can he attached to the ring. This precaution is necessary to prevent the wire flying upwards when the sinker strikes bottom, and relieves the wire of its tension, otherwise, it would be apt to take in kinks and break, as in the other case mentioned.
Now a man has been attending at the pendant with the weights during this time, and, being all ready, the officer in charge has the wire unclamped and lets it run slowly at first; then, when well started, directs some of the weights to be taken off to allow the wire to run more freely, but it is never allowed to run out faster than at the rate of 100 fathoms in 50 seconds, and seldom, at less rate than a minute.
For instance, at the beginning of the mast, the weights on the pendant generally aggregate 90 lbs.—the indication shown by the dynamometer being 37 lbs., and when the wire is going out with the greatest speed admissable the pendant weight is 25 lbs. and the indication shown by the dynamometer 15 lbs.
On the left side of the drum is attached a counter which registers the number of revolutions, and an officer stands with watch and book in hand to note the time of each 100 fathoms running out. The wire has previously been carefully measured as it was wound on the drum, the number of fathoms in each splice being registered in the book; thus when bottom is reached, the depth is known with great accuracy, especially as there is no appreciable stretch to the wire, as there is to rope or cord.
Now when it is supposed the sinker is nearing the bottom, the speed of egress is diminished by replacing the weight up to 90 lbs. or 100 lbs., the dynamometer showing from 35 lbs. to 40 lbs.
The moment the sinker strikes bottom it becomes detached, and the strain which has retarded the descent of the sinker, is now only resisted by the weight of the wire, and pulls back with a force equal to the weight of the shot now resting on the bottom. This causes the index hand of the dynamometer to fly up, and the drum to stop revolving. So perfect and unmistakable are the indications at whatever depth, that a person standing in any part of the ship and looking at the machine, can tell the moment bottom is reached. In reeling in, the dynamometer wheel is unshipped, and the pulley line is shifted for a larger one. The inventor’s plan was to reel in by men hauling in on the pulley line, hand over hand, but after a while a heavy balance wheel was fitted for reeling in on board the Tuscarora, enabling four men to do the work with more ease, facility and quickness, than six men could do it under the old method.
As compared with rope, the time of the running out of the wire is about the same, the great gain being, in reeling in. For instance, Prof. Wyville Thomson states in his “Depths of the Sea,” that sounding from H. M. S. “Porcupine,” in 2435 fathoms, the deepest cast made from that vessel, the time occupied in descent of the line was 33 minutes, 35 seconds, and in “heaving up” 2 hours, 2 minutes; while on board the Tuscarora a cast was had in 2565 fathoms, the time of running out being 31 minutes, 7 seconds, and of reeling in, 39 minutes, 42 seconds, or a gain of nearly a hundred per cent in the total time occupied in the cast. And I can but consider the difference in accuracy in favor of the wire, to be somewhat in the same proportion; for a sinker attached to that light, thin attenuated material, goes straight to the bottom like a plummet dropping into a well, opposing an almost inappreciable surface to the action of ocean currents, while rope or cord, comparatively heavy, presents a not inconsiderable and rough surface, developing a good deal of friction as it runs down to great depths, and curves and bends in all directions in meeting the under currents, and the percentage of stretch should by no means be lost sight of.
When sounding, serial temperatures are taken at the same time from the topgallant forecastle with a duplicate Thomson machine. For instance, if the temperature is desired for every 100 fathoms below the surface down to 500 fathoms, a 7 lb. lead and a Miller-Casella thermometer is attached to the wire. Then the wire is allowed to rim out slowly till the 100 fathom mark is reached and another thermometer is attached, and so on, till the desired depth is reached, and thus, at one serial sounding, the several temperatures are taken. The thermometers are very accurate in their indications, as found by their close correspondence in the many series of temperatures observed.
In the Central North Pacific, from San Diego to the Bonin Islands, the under temperature curve of 40° F. is found to range from 400 fathoms to 500 fathoms in depth. At 1200 fathoms about the lowest temperature is reached; from that depth downward, the thermometer shows a uniform temperature of from 33° to 34° F., and the copper cases enclosing the thermometers come up from the bottom feeling very cold.
In September 1873, the Tuscarora sounded 1100 miles on a great circle from Cape Flattery, Washington Territory, towards Atcha, one of the Aleutian Islands. The work was then suspended owing to the lateness of the season. About 200 miles from Cape Flattery, a submarine elevation of 1800 feet was found, which is probably an under spur from Vancouver Island. From that point to the locality where the ship stopped work, the bottom descends in a remarkably regular manner, averaging a fall of about six feet per mile. Indeed, that part of the Pacific bed may he likened to a section of an immense shallow bowl, so gentle and regular is the curve of descent.
The character of the bottom varied considerably, mud, stiff clay, ooze, sand, pebbles and shingle being brought up at different points on the line sounded; in that respect differing materially from the character of the soil on the telegraphic plateau of the North Atlantic, which is almost precisely uniform in its nature throughout its whole extent.
On the way back to San Francisco, and from San Francisco to San Diego, soundings were made off and on the coast to determine the “True continental outline, or the beginning of the ocean bed proper.” The result shown was, that a slope or terrace, from 10 miles to 50 miles in width, makes off from the coast line in comparatively shoal water, and then drops very abruptly down to depths of 1,500 fathoms and 2,000 fathoms, constituting an immense buttress, as it were, to support the continent.
While sounding late one afternoon, some 140 miles off the coast of California, the lead suddenly brought up at a depth of 996 fathoms, where a depth of 1,600 fathoms or 1,700 fathoms was looked for. No specimen came up and the point of the end was found to be battered.
Sounding round the locality it was found that a rocky submarine peak, 4,000 feet in height, existed in that part of the ocean, rising very abruptly from the ocean bed on northern, eastern and western sides, with a gentle slope on its southern face.
The ocean bed between San Diego and the Hawaiian Islands is like the Atlantic plateau, gently undulating, but differs in this respect, that it is boldly abrupt near the respective coasts; the character of the bottom soil—a light yellowish brown mud or ooze,—is nearly uniform.
Not so the bed from the Hawaiian Islands westward, which is irregular and mountainous, and the nature of the bottom soil dissimilar,—coral limestone, lumps of lava, coarse sand and ooze, containing particles of lava, coming up in specimen cylinders at various localities on the route sounded. Six (6) submarine elevations, ranging from 7,000 feet to near 13,000 feet in height were found, and the evidence seems indisputable that the entire region west of the Hawaiian group has been subjected, at some remote period, to volcanic disturbances. Professor Dana, the great authority on corals, states, the range of living corals to be no more than 120 feet in depth. Where then, did the disintegrated coral, brought up from the mountain peaks 11,000 feet below the surface come from? The answer would seem to point to the former elevation of these peaks, and their gradual subsidence during the long epochs of geological action.
The theory has been that the greatest depth in the Pacific would be found in its eastern part, but so far as the question relates to the North Pacific, the line of soundings run by the Tuscarora would seem to prove to the contrary, the deepest water having been found near the Bonin Islands.
The deepest water found between San Diego and Japan viâ the Bonin Islands was 3,287 fathoms, (19,722 feet), or, about three and three quarters statute miles, and as the weight of a column of water one inch square, is about a ton for every 800 fathoms, it follows that the pressure at that enormous depth amounts to four (4) tons per square inch. The total time occupied in sounding to that great depth and bringing back a bottom specimen, was 1 hour, 56 minutes, 32 seconds. The quickest time was made, when sounding at a depth of 3009 fathoms, which occupied 1 hour, 29 minutes, 32 seconds only.
The soundings are made at night as well as by day, and the incomparable working of the Thomson machine is a source of never ending wonder and admiration to all who witness it.
Nor is it a small gratification to receive back the specimen cups and thermometers which have travelled down so far, and snatched answers from those dark mysterious abysses which the heart of man has ever been questioning with but faintest replies.
[1]This paper has been hastily prepared, and is with diffidence respectfully submitted to the Asiatic Society of Japan.
GEO. E. BELKNAP,
Owing to the absence of the Recording Secretary the Minutes of the last Meeting were not read.
Printed copies of the Amended Constitution and By-Laws were laid on the table for the use of the members. Some Fossils were presented by Judge Goodwin, and a Crinoid from Inoshima by Rev. Mr. Cooper. Also a copy of Vol. I. of Botanical Researches in Japan by Dr. Sabatier of Yokoska.
The names of the following gentlemen, as new members, were announced:—Messrs. C. W. Goodwin, C. W. Kinder, Herbert Cope, John J. Quin, F. Ringer, J. C. Smith, T. B. Glover, Alex. Wright, D. D Inglis, J. J. Van der Pot, F. Heelyer, and Rev. H. Burnside.
A Committee was appointed to confer with the Literary Society on the subject of a new Hall to be occupied by the two Societies conjointly.
In the absence of the writer, C. W. Lawrence, Esq. of H. B. M. Legation, a paper “Notes of a Journey in Hatachi, Shimôsa and Kadzusa” was read by Mr. Satow; who afterwards explained in answer to an enquiry, that the removal of Buddhist Shrines and Temples about which so much had been said recently, was to be understood—not as an endeavour to extirpate Buddhism, but only as a clearing away from Shintô grounds and temples of what had been intruded there during the Shôgunate.
The Corresponding Secretary then read a paper by Captain Belknap, of the S. S. Tuscarora on Deep Sea Soundings, which was followed by explanations by Captain Belknap himself of the apparatus employed in the soundings; and also of a Diagram exhibiting an outline of the ocean bed from San Diego, in California, to the Sandwich Islands; thence to the Bonin Islands, and thence to Japan. The future line of soundings is to run along by the Aleutian Islands to Alsaka.
The President tendered the thanks of the Society—afterwards confirmed by a special vote—and remarked on the exceptional value and interest of papers such as that just read.
Prof. W. E. Ayrton said:—
Captain Belknap has ably described in his paper the history of deep sea sounding apparatus. As he has said, the methods by which attempts have been made to obtain accurate results may be divided into four classes— the use of a very heavy weight to keep the line approximately vertical, which weight had to be left at the bottom at every sounding so that the mere cost of metal thrown away was, in a long expedition like the present, considerable—next, an apparatus like a patent-log which recorded on a tell-tale arrangement attached to it, its descent in the sea—thirdly, sounding by time, in which case there was attached to the weight only a very light line the object of which was merely to determine when the weight reached the bottom, it having been proved that a body falling unimpeded through water moves through equal spaces in equal times, quite unlike the case of a falling body in air, where if the time is doubled the space is quadrupled; with this latter method of sounding, however, not only the weight but the cord was also lost. All the above methods have proved more or less unsatisfactory in deep seas where there are surface or under-currents. After the paper we have heard from Captain Belknap, bearing valuable testimony as it does to the efficiency of Sir William Thomson's piano-forte wire arrangement, it is with diffidence that I am now going to say a few words regarding that system. Perhaps the fact of my having been present on the occasion when Sir William first brought his method before the notice of public, at the Meeting of the British Association held at Brighton in 1872, now enables me to say something about the line of thought which gave birth to this invention and may plead as an excuse for my apparently trenching on a subject Captain Belknap has made so throughly his own. Owing to that little hesitation naturally displayed by Mr. Syle regarding the infliction on the company of the valuable technical details contained in the paper we have just heard him read, I am afraid that the points of merit of the Thompson apparatus may not have been made clear to some of those present. It was quite evident to Sir William that in order to have accurate deep sea soundings fine wire and not cord must be used; the first point, therefore, was to devise a contrivance by which the paying out wheel should be automatically stopped the moment the weight reached the bottom. This he has succeeded in doing in a very ingenious way. To the end of the wire a small weight is attached; to this, one end of twenty-five fathoms of rope, to the other end of which hangs a much larger weight with a cup for bringing up specimens from the bottom. The existence of the two weights and the very important part played by them was not, I think, grasped by many during the reading of the paper. This wire is wound on a drum, made as little massive as possible. The motion of the drum is regulated by an exceedingly simple friction break, which is so adjusted that when the lower and heavier weight has nearly reached the bottom the retarding force is a little less than the total strain on the wire, but much greater than that strain becomes when the lower weight rests on the bottom, consequently the moment the bed of the ocean is reached the paying out gear automatically stops,—the wire hangs practically vertical without slack, and the total amount run out indicates the true depth. After arranging this apparatus one of the early difficulties experienced by Sir William was to obtain thin wire of sufficient strength. This he at last succeed in doing by the employment of piano-forte wire. But as the thin piano-forte wire is not that which is commonly used for sounding the deep C, considerable judgment had to be employed in the selection of wire of only the best quality. Another difficulty experienced was that it was necessary to make the drum on which the wire was wound very slight, for unless its mass is kept small the momentum the wheel would acquire by its rapid rotation would be such as to prevent it being suddenly stopped by the friction break when the weight reached the bottom. On the first trial of this apparatus when Sir William was making soundings in the Bay of Biscay the accumulated strain of the wire, produced on coiling in, completely crushed the slight drum on which it was wound, so that it became necessary for those engaged to seize the wire with their hands to pull it up. However, although the depth of the sea there is over twelve hundred fathoms, and although there were only two or three men in the small boat from which the soundings were being made, Sir William succeeded, by aid of that indomitable energy and perseverance that has characterised all his undertakings, in bringing up specimens of the bottom which he exhibited at that meeting of the British Association. Perhaps Captain Belknap will kindly give as the results of his experience with reference to the crushing of the drum, also whether he knows why the Challenger has made, as far as I know, no use of the wire apparatus that was supplied them.
Captain Belknap, in reply to various inquiries, stated that they had been quite successful in bringing up specimens of the bottom; that corals were found at a depth hitherto unthought-of; that evidences of life were found at the greatest depths; and that he had found it necessary once and again to strengthen the drum employed in the method of Sir Wm. Thompson, with whose views he was well acquainted, and who sympathized cordially with the work now being performed by the Tuscarora.- ↑ Erratum—p. 190, line 14, after the words “steam is ready” insert the words “and the ship brought stern to wind and sea.”