DREDGING IN MODERN TIMES—WHAT IT HAS TAUGHT US—DEEP SEA SOUNDINGS—FIRST ATTEMPTS—IMPLEMENTS USED FOR IT—THE CHANCE FOR INVENTORS.

In modern times we have learned a great deal more of the ocean than the ancients knew, from dredging. By this means we have become acquainted not only with the outline of the bottom, but have also become acquainted with the temperature of deep seas, with the varied forms of animal and vegetable life which are present there, and have come to know, with far greater certainty and completeness than ever before, the part which the ocean has played and is still playing in the preparation of the land.

By sounding, the ancients, of course, knew the depths of the shallow waters along their coasts. It would be the most natural thing for a sailor to tie a stone to a string, and let it down into the water, when he wanted to know whether it was deep enough to float his vessel, and the same means would also be used to discover whether there were any sunken rocks in such harbors as he was frequenting. But the ocean, to all antiquity, was unfathomable; they dared not attempt to cross it, and of course did not think they could measure its depth. Long after the ocean had been crossed by ships the belief was still current that it was impossible to measure its depth, and this belief was made the stronger by the unsuccessful attempts made in mid ocean to obtain soundings with the ordinary lead and line.

Before we arrived at a positive knowledge of the depth of the ocean, scientific men attempted to calculate it by various methods. Laplace, calculating the mean elevation of the land, supposed the sea must be of about equal depth. Young, drawing his deductions from the tides, calculated the depth of the sea. This method has been recently used to calculate the depth of the Pacific. A wave of a certain velocity indicates water of such a depth. In the case of the earthquake of 1854, in Japan, which caused a wave that extended to California, the rate of its progress afforded an indication of the mean depth of the sea it passed over, and authentic soundings taken since have confirmed the general accuracy of the calculation.

The ordinary lead used for soundings is a pyramid of lead, the bottom of which has a depression in it, which is filled with tallow; on striking the bottom a little of the sand or mud adheres to this tallow and is brought up to the surface. In this way something is learned about the depth and bottom of the sea, but not enough to satisfy the naturalists, who inquired whether it might not be possible to dredge the bottom of the sea in the ordinary way, and to send down water bottles and registering instruments to settle finally the conditions of the deep waters, and determine with precision the composition and temperature at great depths.

An investigation of this kind is beyond the powers of private enterprise. It requires more power and sea skill than naturalists usually have. It is a work for governments. That of the United States has contributed fully its share. The coast survey has added a great deal to our knowledge of the deep sea, and the ships of the navy took part in the soundings by which the existence of the plateau across the bed of the North Atlantic, which has been used for the ocean telegraphic cable, was proved.

In 1868 the English government provided the vessels and crews for the purpose of conducting deep sea dredgings, under the direction of Dr. Carpenter and Mr. Wyville Thompson. These expeditions have found that it is quite possible to work with certainty, though not with such ease, at the depth of 600 fathoms, as at a depth of 100; and in 1869 it carried on deep sea dredging at a depth of 2,435 fathoms, 14,610 feet, or very nearly three miles, with perfect success. Dredging in such deep water is very trying. Each haul occupied seven or eight hours, and during the whole of this time the constant attention of the commander was necessary, who stood with his hand on the regulator of the accumulator, ready at any moment to ease an undue strain, by a turn of the ship's paddles. The men, stimulated and encouraged by the cordial interest taken by the officers in the operations, worked with a willing spirit; but the labor of taking up three miles of rope, coming up with a heavy strain, was very severe. The rope itself, of the very best Italian hemp, 2 1/2 inches in circumference, with a breaking strain of 2 1/4 tons, looked frayed out and worn, as if it could not have been trusted to stand such an extraordinary ordeal much longer.

The ordinary deep sea lead used for soundings weighs from 80 to 120 pounds. The samples of the bottom which it brings up are marked upon the charts as mud, shells, gravel, ooze or sand, thus 2,000 m. sh. s. means mud, shells and sand at 2,000 fathoms; 2,050 oz. st. means ooze and stones at 2,050 fathoms; 2,200 m. s. sh. sc. means mud, sand, shells, and scoriÆ, at 2,200 fathoms, and so on. When no bottom is found with the lead it is entered on the chart thus:——3,200, meaning no bottom was reached at that depth.

This method of sounding answers very well for comparatively shallow water, but it is useless for depths much over 1,000 fathoms, or six thousand feet. The weight is not sufficient to carry the line rapidly and vertically to the bottom; and if a heavier weight is used, the ordinary sounding line is not strong enough to draw up its own weight, and that of the lead from a great depth, and so breaks. No impulse is felt when the lead touches the bottom, and so the line continues running out, and any attempt to stop it breaks it. In some cases the slack of the line is carried along by currents, and in others it is found that the line has been running out by its own weight and coiling in a tangled mass on top of the lead.

These sources of error vitiate the results of very deep soundings. Thus Lieutenant Walsh, of the U.S. schooner Taney, reported 34,000 feet without touching bottom; and the U.S. brig Dolphin used a line 39,000 feet long without reaching bottom. An English ship reported 46,000 feet in the South Atlantic and the U.S. ship Congress 50,000 feet without touching bottom. These are, however, known to be errors, so that no soundings are entered on charts over 4,000 feet, and few over 3,000. The U.S. Navy introduced the first great improvement in deep soundings. This consisted in using a heavy weight and a small line. The weight, a 32 or 68-pound shot, was rapidly run down, and when it touched bottom, which was shown by the sudden change in the rapidity with which the line was run out, the line was cut and the depth estimated from the length of cord remaining on the reel. This, however, cost the loss of the shot and the line for each sounding.

One of the first attempts at deep sea dredging was made in 1818, by Sir John Ross, in command of the English navy vessel Isabella, on a voyage for the exploration of Baffin's Bay with a machine of his own invention, which he called a "deep sea clamm." It consisted of a pair of forceps, kept apart by a bolt, and so contrived that when the bolt struck the ground a heavy iron weight slipped down a spindle and closed the forceps, which retained a portion of the mud, sand, or small stones, from the bottom. With this instrument he sounded in 1,050 fathoms, and brought up six pounds of very soft mud, using a whale line, made of the best hemp, and measuring 2 1/2 inches in circumference.

The cup lead is another invention. With this there is a pointed cup at the bottom of the lead, fastened to it with a rod upon which a circular plate of leather plays, serving as a cover to the cup. As it strikes the bottom, the cup is driven in the mud, and on hauling up the cover is pressed into the cup by the water, and brings up the mud it contains. The objection to this is that it is too crude; in its passage up, the water washes away the mud, so that only on an average of once in three times does the cup come up with anything in it; and deep sea soundings take too much time, and are too valuable, to admit so large an average of loss.

About 1854 Mr. J. M. Brooke, of the U.S. Navy, who was at the time associated with Prof. Maury, so well known for his labor in gathering and diffusing a knowledge of the currents of the ocean, invented a deep sea sounding apparatus, which is known by his name. It is still in use, and all the more recent contrivances have been, to a great extent, only modifications and improvements upon the original idea, that of detatching the weight. The instrument is very simple. A 64-pound shot is cast with a hole in it. An iron rod, with a cavity in its end, fits loosely in the hole in the shot. Two movable arms at the top of the rod are furnished with eyes holding ends of a sling in which the ball hangs. The cavity at the end of the rod is furnished with tallow, and the apparatus is let down. On reaching the bottom, the rod is forced into the mud, the cavity becomes filled with it, and there being no more tension, on the rope holding up the movable arms, they fall, disengage the ends of the sling, and allow the ball to slide down the rod. The rod is then withdrawn, carrying up the portion of the bottom secured in the cavity at its foot, and leaving the ball on the bottom. This apparatus costs a ball each time it is used, and brings up but a small portion of the bottom, which is also apt to be diminished on its way to the top, by the water it passes through.

Commander Dayman, of the English Navy, in 1857 invented an improvement upon Mr. Brooke's original invention. He used iron wire braces to support the sinker, as these detach more easily than slings of rope. The shot he replaced by a cylinder of lead, as offering less surface to the water in its descent, and he fitted the cavity in the bottom of the rod with a valve opening inward. Commander Dayman used the apparatus, with these modifications, in the important series of soundings he made in the North Atlantic, while engaged in surveying the plateau for the ocean telegraphic cable, and reports that it worked well.

The apparatus known as the bull-dog machine is an adaptation of Sir John Ross' deep-sea clamms, together with Brooke's idea of disengaging the weight. It was invented during the cruise of the English Navy vessel, the Bull-dog, in 1860, and the chief credit for it belongs to the assistant engineer during that cruise, Mr. Steil. A pair of scoops are hinged together like a pair of scissors, the handles represented by B. These are permanently fastened to the sounding rope, F, which is here represented as hanging loose, by the spindle of the scoops. Attached to this spindle is the rope, D, ending in a ring. E represents a pair of tumbler hooks, like those used so generally. C is a heavy weight, of iron or lead, hollow, with a hole large enough for the ring upon D to pass through. B is an elastic ring of India rubber, fitted to the handles of the scoops, and designed to shut them together as soon as the weight, C, which now holds them apart, is removed. When the bottom is reached, the scoops, open, are driven into the ground, the tension on the rope ceases, the tumbler hooks open and release the weight, which falls on its side, and allows the elastic ring to shut the scoops, inclosing a portion of the bottom in which they have been forced. The trouble with this apparatus is its complicated character; pebbles may get in the hinge and prevent the scoops from closing. In all apparatus to be used for such a purpose the greater the simplicity the better, and an invention, which shall at once be simple and effective, capable of bringing up a pound or two from the bottom at a depth of 2,000 fathoms or more, without fail, and without too much trouble, is still a desideratum, and its invention is well worth the attention of the ingenious.

Another arrangement, called the Hydra sounding machine, is intended to bring up portions of the bottom and water from the lowest strata reached. It consists of a strong brass tube, which unscrews into four chambers, closed with valves, opening upward, so that in the descent the water passes through them, freely; but when it is commenced to haul up, the pressure of the water closes the valves. This apparatus is also furnished with weights to sink it, which are released, on reaching the bottom, by a similar method to those described. This instrument was used during the deep sea sounding cruise of the Porcupine, and never once failed. Its faults are its complication, and that it brings up only small samples of the bottom. Captain Calver, who used it, could always, when at the greatest depths, distinctly feel the shock of the arrest of the weight upon the bottom communicated to his hand.

Various attempts have been made to construct instruments which should accurately determine the amount of the vertical descent of the lead by self-registering machinery. The most successful and the one most commonly used is Massey's sounding machine. This instrument, in its most improved form, is shown in the accompanying cut. It consists of a heavy oval brass shield, furnished with a ring at each end of its longer axis. To one of these a sounding rope is attached, and to the other, the weight is fastened at about a half fathom below the shield. A set of four brass wings or vanes are set obliquely to an axis, so that, like a windmill or propeller wheels, it shall turn by the force of the water as it descends. This axis communicates its motion to the indicator, which marks the number of revolutions on the dial plate. One of these dials marks every fathom, and the other every fifteen fathoms of descent. This sounding machine answers very well in moderately deep water, and is very valuable for correcting soundings by the lead alone, where deep currents are suspected, as it is designed to register vertical descent alone. In very deep water it is not satisfactory, from some reason which it is difficult to determine. The most probable explanation is that it shares the uncertainty inherent in all instruments using metal wheel work. Their machinery seems to get jammed in some way, under the enormous pressure of the water, at great depths.

To ascertain the surface temperature of the water of the sea is simple enough. A bucket of water is drawn up, and a thermometer is placed in it. With an observation of this kind the height of the thermometer in the air should be always noted. Until very recently, however, very little or nothing was known with any certainty about the temperature of the sea at depths below the surface. Yet this is a field of inquiry of very great importance in physical geography, since an accurate determination of the temperature at different depths is certainly the best, and frequently the only means, for determining the depth, the width, the direction and general path of the warm ocean currents, which are the chief agents in diffusing the equatorial heat; and more especially of those deeper currents of cold water which return from the poles to supply their places, and complete the watery circulation of the globe. The main cause of this want of accurate knowledge of deep sea temperatures is undoubtedly the defective character of the instruments which have been hitherto employed.

The thermometer which has been generally used for making observations on the temperature of deep water is that known as Six's self-regulating thermometer, inclosed in a strong copper case, with valves or apertures above and below, to allow a free passage of the water through the case and over the face of the instrument. This registering thermometer, consists of a glass tube, bent in the form of a U. One arm terminates in a large bulb, entirely filled with a mixture of creosote and water. The bend in the tube contains a column of mercury, and the other arm ends in a small bulb, partly filled with creosote and water, but with a large space empty, or rather filled with the vapor of the mixture and compressed air. A small steel index with a hair tied round it, so as to act like a spring against the side of the tube, and keep the index at any point it may assume, lies free in either arm, among the creosote, floating on the mercury. This thermometer gives its indications only from the expansions and contractions of the liquid in the large full bulb, and consequently is liable to some slight error, from the variations of temperature upon the liquids in other parts of the tube. When the liquid in the large bulb expands, the column of mercury is driven upward toward the half-empty bulb, and the limb of the tube in which it rises is graduated from below, upward, for increasing heat. When the liquid contracts in the bulb, the mercury rises in this arm of the tube, which is graduated from above downward, but falls in the other arm. When the thermometer is going to be used, the steel indices are drawn down in each limb of the tube, by a strong magnet, till they rest, in each arm, upon the surface of the mercury. When the thermometer is drawn up from deep water, the height at which the lower end of the index stands in each tube indicates the limit to which the index has been driven by the mercury, the extreme of heat or cold to which the instrument has been exposed. Unfortunately, the accuracy of the ordinary Six's thermometer cannot be depended upon beyond a very limited depth, for the glass bulb which contains the expanding fluid yields to the pressure of the water, and compressing the contained fluid, gives an indication higher than is due to temperature alone. This cause of error is not constant, since the amount to which the bulb is compressed depends upon the thickness and quality of the glass. Yet, as in thoroughly well-made thermometers, the error from pressure is pretty constant, it has been proposed to make a scale, from an extended series of observations, which might be used to correct the observations, and thus closely approximate the truth.

A better plan has been proposed, and being practically applied, has been found to work very well. This consists in incasing the full bulb in an outer covering of glass, so that there shall be a coating of air between the bulb and the outside coating, and that this air being compressed by the pressure of the water outside, shall thus protect the inside bulb. Observations taken in 1869 with thermometers constructed in this way, as deep as 2,435 fathoms, in no instance gave the least reason to doubt their accuracy. A modification of the metallic thermometer, invented by Mr. Joseph Saxton, of the United States office of weights and measures, for the use of the coast survey, may be thus described. A ribbon of platinum and one of silver are soldered with silver solder to an intermediate plate of gold, and this compound ribbon is coiled round a central axis of brass, with the silver inside. Silver is the most expansible of the metals under the influence of heat, and platinum nearly the least. Gold holds an intermediate place, and its intervention between the platinum and silver moderates the strain and prevents the coil from cracking. The lower end of the coil is fixed to the brazen axis, while the upper end is fastened to the base of a short cylinder. Any variation of temperature causes the coil to wind or unwind and its motion rotates the axial stem. This motion is increased by multiplying wheels, and is registered upon the dial of the instrument by an index, which pushes before it a registering hand, moving with sufficient friction to retain its place, when pushed forward. The instrument is graduated by experiment. The brass and silver parts are thickly gilt by the electrotype process, so as to prevent their being acted upon by the salt water.

The box in which the instrument is protected is open to admit the free passage of the water. This instrument seems to answer very well for moderate depths. Up to six hundred fathoms its error does not exceed a half degree, centigrade; at 1,500 fathoms it rises however to five degrees, quite as much as an unprotected Six thermometer, and the error is not so constant. Instruments which depend for their accuracy upon the working of metal machinery cannot be depended upon when subjected to the great pressure of deep soundings.

For taking bottom temperatures at great depths, two or more of the thermometers are lashed to the sounding line at a little distance from each other, a few feet above the sounding instrument. The lead is rapidly run down, and after the bottom is reached an interval of five or ten minutes is allowed before hauling in. In taking serial temperature soundings, which are to determine the temperature at certain intervals of depth the thermometers are lashed to an ordinary deep sea lead, the required quantity of line for each observation of the series ran out, and the thermometers and lead are hove each time. The operation is very tedious; a series of such observations in the Bay of Biscay, where the depth was 850 fathoms and the temperature taken for every fifty fathoms, occupied a whole day. In taking bottom temperatures with a self-registering thermometer, the instrument of course simply indicates the lowest temperature to which it has been subjected, so that if the bottom stratum is warmer than any other through which the thermometer has passed, the result would be erroneous. This is only to be tested by serial observations; but from these it appears, wherever they have been made, that the temperature sinks gradually, sometimes very steadily, sometimes irregularly from the surface to the bottom, the bottom water being always the coldest.

Several important facts of very general application in physical geography have been settled by the deep sea temperature soundings which have been recently made, and the theories formerly held on this subject shown to be erroneous. It has been shown that in nature, as in the experiments of M. Despretz, sea water does not share in the peculiarities of fresh water, which, as has been long known, attains its maximum density at four degrees, centigrade; but like most other liquids increases in density to its freezing point; and it has also been shown that, owing to the movement of great bodies of water at different temperatures in different directions, we may have in close proximity two ocean areas with totally different bottom climates, a fact which, taken along with the discovery of abundant animal life at all depths, has most important bearings upon the distribution of marine life, and upon the interpretation of palaeontological data.

Mr. Wyville Thompson, who conducted the series of important deep sea soundings undertaken in the Porcupine, says very truly, "It had a strange interest to see these little instruments, upon whose construction so much skilled labor and consideration had been lavished, consigned to their long and hazardous journey, and their return eagerly watched for by a knot of thoughtful men, standing, note-book in hand, ready to register this first message, which should throw so much light upon the physical conditions of a hitherto unknown world."

Up to the middle of the last century the little that was known of the inhabitants of the bottom of the sea beyond low water mark, appears to have been gathered almost entirely from the few objects thrown up on the beaches after storms or from chance specimens brought up on sounding lines, or by fishermen engaged in sea fishing or dredging for oysters. From this last source, however, it was almost impossible to obtain specimens, since the fishermen were superstitious concerning bringing home anything but the regular objects of their industry, and from a fear that the singular things which sometimes they drew up might be devils in disguise, with possibly the power to injure the success of their business, threw them again, as soon as caught, back into the sea. Such superstitions are dying out, and in fact so singular are many of the animals hid in the depths of the sea; their forms and general air are so different from anything which the fishermen were used to see, that we can hardly wonder at the fear they excited. When, however, the attention of naturalists was turned toward the sea, they used the dredge such as was used by the oyster fishermen, and all the dredges now in use are simply modifications of this.

The dredge for deep sea operations is made with two scrapers, so that it shall always present a scraping surface to the bottom, however it may fall. The iron work should be of the very best, and weighing about twenty pounds. The bag is about two feet deep, and is a hand-made net of very strong twine, the meshes half an inch to the side. As so open a net-work would let many small things through, the bottom of the bag, to the height of about nine inches, is lined with a light open kind of canvas, called by the sailors "bread-bag." Raw hides have been used for making the dredge bag, but, though very strong, they are apt to become too much so to another sense than touch. It is bad economy to use too light a rope in such operations, and best to fasten it to only one arm of the dredge, the eyes of the two arms being tied together with a thinner cord. In case, then, the dredge becomes entangled at the bottom, this cord will break first, and thus releasing one of the arms of the dredge, may so change the direction of the strain upon the rope as to free the dredge itself.

Dredging in deep water, that is, at depths beyond 200 fathoms, is a matter of some difficulty, and can hardly be done with the ordinary machinery at the disposal of amateurs. The description of the apparatus used in the Porcupine, in 1869 and '70, on her dredging cruise in the Bay of Biscay, will show what is necessary. These arrangements are also shown in the cut. This vessel, a gun-boat of the English navy, of 382 tons, was fitted out specially for this work. Amidships she was furnished with a double cylinder donkey-engine, of about twelve horse-power, with drums of various sizes, large and small. The large drum was generally used, except when the cord was too heavy, and brought up the rope at a uniform rate of more than a foot a second. A powerful derrick projected over the port bow, and another, not so strong, over the stern. Either of these was used for dredging, but the one at the stern was generally used for soundings. The arrangement for stowing away the dredge rope was such as made its manipulation singularly easy, notwithstanding its great weight, about 5,500 pounds. A row of some twenty large pins of iron, about two feet and a half long, projected over one side of the quarterdeck, rising obliquely from the top of the bulwark. Each of these held a coil of from two to three hundred fathoms, and the rope was coiled continuously along the whole row. When the dredge was going down, the rope was taken rapidly by the men from these pins in succession, beginning from the one nearest the dredging derrick, and in hauling up a relay of men carried the rope from the drum of the donkey-engine and laid it in coils on the pins, in reverse order. The length of the dredge rope was 3,000 fathoms, nearly three and a half miles. Of this, 2,000 fathoms were hawser-laid, of the best Russian hemp, 2 1/2 inches in circumference, with a breaking strain of 2 1/4 tons. The 1,000 fathoms next the dredge were hawser laid, 2 inches in circumference. Russia hemp seems to be the best material for such a purpose. Manilla is considerably stronger for a steady pull, but is more likely to break at a kink.

The frame of the largest dredge used weighed 225 pounds. The bag was double, the outside of strong twine netting, lined with canvass. Three sinkers, one of 100 pounds, and two of 56 pounds each, were attached to the dredge rope at 500 fathoms from the dredge. A description of the sounding made in the Bay of Biscay on the 22d of July, 1869, will give an idea of the process. When the depth had been ascertained, the dredge was let go about 4:45 p.m., the vessel drifting slowly before a moderate breeze. At 5:50 p.m. the whole 3,000 fathoms of rope were out. While the dredge is going down the vessel drifts gradually to leeward; and when the whole 3,000 fathoms of rope are out, she has moved so as to make the line from the dredge slant. The vessel now steams slowly to windward, and is then allowed to drift again before the wind. The tension of the vessel's motion, thus instead of acting immediately on the dredge, now drags forward the weight, so that the dredging is carried on from the weight and not directly from the vessel The dredge is thus quietly pulled along, with the lip scraping the bottom, in the position it naturally assumes from the center of weight of its iron frame and arms. If, on the contrary, the weights were hung close to the dredge, and the dredge was dragged directly from the vessel, owing to the great weight and spring of the rope the arms would be continually lifted up, and the lip of the dredge be prevented from scraping. In very deep water this operation of steaming up to windward until the dredge rope is nearly perpendicular, after drifting for half an hour or so to leeward, is usually repeated three or four times. At 8:50 p.m. hauling-in is commenced, and the donkey-engine delivers the rope at a little more than a foot a second. A few moments before 1 o'clock in the morning the weights appear, and a little after one, eight hours after it was cast, the dredge appears and is safely landed on deck, having in the meantime made a journey of over eight miles. The dredge, as the result of this haul, contained 1 1/2 hundred weight of characteristic pale grey Atlantic ooze. The total weight brought up by the engine was as follows:

In many of the dredgings at all depths it was found that while few objects of interest were brought up within the dredge, many echinoderms, corals and sponges came to the surface sticking to the outside of the dredge bag, and even to the first few fathoms of the rope. The experiment was therefore tried of fastening to a rod attached to the bottom of the dredge bag, a half dozen swabs, such bundles of hemp as are used on ship-board for washing the decks. The result was marvelous; the tangled hemp brought up everything rough and movable that came in its way, and swept the bottom of the ocean as it would have swept the deck. So successful was this experiment, that the hempen tangles are now regarded as an essential adjunct to the dredge, and nearly as important as the dredge itself, and when the ground is too rough for using the dredge, the tangles alone are used.

The mollusca have the best chance of being caught in the dredge; their shells are comparatively small bodies mixed with the stones on the bottom, and they enter the dredge with these. Echinoderms, corals and sponges, on the contrary, are bulky objects, and are frequently partially buried in the mud, or more or less firmly attached, so that the dredge generally misses them. With the tangles it is the reverse, the smooth heavy shells are rarely brought up, while the tangles are frequently loaded with specimens; on one occasion not less than 20,000 examples came up on the tangles in a single haul.

In the Porcupine both derricks were furnished with accumulators, which were found of great value. The block through which the sounding line or dredging rope passed was not attached directly to the derrick, but to a rope which passed through an eye at the end of the spar, and was fixed to a bitt on the deck. On a bight of this rope, between the block and the bitt, the accumulator was lashed. This consists of thirty or forty, or more, vulcanized india-rubber springs, fastened together at the two extremities, and kept free from each other by being passed through holes in two wooden ends like barrel heads. The loop of the rope is made long enough to permit the accumulator to stretch to double or treble its length, but it is arrested far within its breaking point. The accumulator is valuable in the first place as indicating roughly the amount of strain upon the line; and in order that it may do so with some degree of accuracy it is so arranged as to play along the derrick, which is graduated, from trial, to the number of hundred weights of strain indicated by the greater or less extension of the accumulator; but its more important function is to take off the suddenness of the strain on the line when the vessel is pitching. The friction of one or two miles of cord in the water is so great as to prevent its yielding to a sudden jerk, such as is given to the attached end when the vessel rises to a sea, and the line is apt to snap.

The results which have been gained by deep sea dredging are so important that the English Government recently fitted out another vessel, the Challenger, for such a cruise, with every appliance. This vessel is now due in New York.