Part 30

The possibility of sudden strain necessitates a constant watching of the dredge rope, as the ship's engines may at any moment be needed to ease the tension by stopping the vessel's way, and the hauling engines by paying out more rope. The use of accumulators both renders the strain more gradual and gives warning of an increase or decrease; indeed they can be calibrated and used as dynamometers to measure the strain. One of the best forms of accumulator consists of a pile of perforated rubber disks, which receive the strain and become compressed in doing so. The arrangement is in essence as follows. The disks form a column resting on a cross-bar or base, from which two rods pass up one on each side of the column. Another cross-bar rests on the top disk, and from it a rod passes freely down the centre perforation of disks and base. Eyes are attached to the lower end of this rod and to a yoke connecting the side rods at the top: a pull exerted on these eyes is thus modified by the elasticity of the dredge. In the "Porcupine" and other early expeditions the accumulator was hung from the main yard arm, and the block through which the dredge rope ran suspended from it. In more recent ships a special derrick boom is rigged for this block, and a second accumulator is sometimes inserted between the topping lift by which this is raised and the end of the boom.

The margin of safety of steel wire rope is much larger than is that of hempen rope, a fact of importance both in towing in a rough sea and in hauling. Galvanized steel wire with a hempen core was first used by Agassiz on the "Blake." He states that his wire weighed one pound per fathom, against two pounds per fathom of hempen rope, and had a breaking strain nearly twice that of hempen rope, which bore two tons. Thus in hauling the wire rope has both greater capability and less actual strain. It has also the advantages of occupying a mere fraction (1/9) of the storage space needed for rope, of lasting much longer, and its vibrations transmit much more rapid and minute indications of the conduct of the dredge.

Wire rope is kept wound on reels supplied with efficient brakes to check or stop its progress, and an engine is often fitted for winding it in and veering it out. From the reel it passes to the drum of the hauling engine, round which it takes some few turns; care is taken by watching or by the use of an automatic regulator (Tanner) that it is taken at a rate equal to that at which it is moving over the side. From the hauling engine it passes over leading wheels (one of which should preferably be a registering wheel and indicate the amount of rope which has passed it), and so it reaches the end of the derrick boom.

The dredge is lowered from the derrick boom, which has been previously trained over to windward so that its end is well clear of the ship, while the ship is slowly moving forward. The rope is checked until the net is seen to be towing clear, and then lowered rapidly. Where a weight is used in front of the trawl Captain Calver successfully adopted the plan of backing after sufficient line had been paid out: the part of the rope from weight to surface thus became more vertical, while the shorter remainder, previously in line with it, sank to the bottom without change of relative position of weight and dredge. The ship was then ready for towing. When no front weight is used the manoeuvre is unnecessary.

There should be a relation maintained between speed of vessel onward and of rope downward, or a foul haul may result owing to the gear capsizing (in the case of a trawl), or getting the net over the mouth (in a dredge). The most satisfactory method of ensuring this relation seems to be so to manage the two speeds that the angle made by the dredge rope is fairly constant. This angle can be observed with a simple clinometer. The following table abridged from Tanner most usefully brings together the requisite angles with other useful quantities.

+----------+----------------+---------+---------------+---------------+ | Depth of | Speed of ship |Length of|Angle of dredge|Angle of dredge| | water. | while shooting | rope | rope while | rope while | | |dredge or trawl.|required.|lowering trawl.|dragging trawl.| +----------+----------------+---------+---------------+---------------+ | Fathoms. | Knots. | Fathoms.| | | | 100 | 3 | 200 | 60 | 55 | | 200 | 3 | 400 | 60 | 55 | | 400 | 3 | 700 | 60 | 52 | | 600 | 2¾ | 1000 | 55 | 50 | | 800 | 2½ | 1200 | 50 | 44 | | 1000 | 2½ | 1500 | 50 | 40 | | 1500 | 2¼ | 2166 | 50 | 40 | | 2000 | 2 | 2670 | 45 | 35 | | 3000 | 2 | 4000 | 40 | 35 | +----------+----------------+---------+---------------+---------------+

The speed of towing, always slow, may be assumed to be approximately correct if the appropriate angle is maintained. Hauling should at first be slow from great depths, but may increase in speed as the gear rises.

For further details of deep-sea dredging, especially of the hauling machinery and management of the gear, the special reports of the various expeditions must be consulted. Commander Tanner, U.S.N., has given in _Deep Sea Exploration_ (1897) a very full and good account of the equipment of an exploring ship; and to this book the present article is much indebted.

_Modifications and Additions to the Dredge._--From 1818, when Sir John Ross brought up a fine Astrophyton from over 800 fathoms on a sounding line in Baffin's Bay, instances gradually accumulated of specimens being obtained from great depths without nets or traps. The naturalists of the "Porcupine" and other expeditions found that echinoderms, corals and sponges were often carried up adhering to the outer surface of the dredge and the last few fathoms of dredge rope. In order to increase the effectiveness of this method of capture a bar was fastened to the bottom of the dredge, to which bunches of teased-out hemp were tied. In this way specimens of the greatest interest, and frequently of equal importance with those in the dredge bag, were obtained. The tangle bar was at first attached to the back of the net. From the "Challenger" expedition onward it has been fixed behind the net by iron bars stretching back from the short sides of the dredge frame which pass through eyes in their first ends (fig. 15). The swabs are thus unable to fold over the mouth of the dredge. Rope lashings to the lips of the dredge are sometimes added, and a weight is tied to the larger bar to keep it down.

[Illustration: FIG. 15.--Deep-sea Dredge, with Tangle Bar.]

Occasionally the tangle bar is used alone (Agassiz), and one form (Tanner) has two bars, stretching back like the side strokes of the letter A from a strong steel spring in the form of an almost complete circle. The whole is pulled forward from a spherical sinker fastened in front of the spring apex; and should the apex enter a crevice between rock masses, the side bars are closed by the pressure instead of catching and bringing up. This is said to be a very useful instrument among corals.

_The Blake Dredge._--In the soft ooze which forms the bottom of deep seas the common dredge sinks and digs much too deeply for its ordinary purpose, owing partly to its chief weight bearing on the frame only,

## partly to its everted lips. To obviate these defects Lieutenant

Commander Sigsbee of the "Blake" devised the Blake dredge. Its novel features were the frame and lips. The former was in the form of a skeleton box; that is, a rectangle of iron bars was placed at the back as well as the front or mouth of the net and four more iron bars connected the two rectangles. The lips instead of being everted were in parallel planes--those, namely, of the top and bottom of the net. The effect of this was to minimize digging and somewhat spread the incidences of the weight. Another advantage was that the net being constantly distended by its frame, and, moreover, protected top and bottom by an external shield of canvas, quite delicate specimens reached the surface uninjured. The dredge weighed 80 lb. and was 4 ft. square and 9 in. deep.

_Rake Dredges._--These are devices for collecting burrowing creatures without filling the dredge with the soil in which they live. Holt used, at Plymouth, a dredge whose side bars and lower lip were of iron, the latter armed with forward and downward pointing teeth which stirred up the sand and its denizens in front of the dredge mouth. The upper lip of the dredge was replaced by a bar of wood. The bag was of cheese-cloth or light open canvas, and the whole was of light construction. The apparatus was very useful in capturing small burrowing crustacea. The Chester rake dredge is a Blake dredge in front of which is secured a heavy iron rectangle with teeth placed almost at right angles to its long sides and in the plane of the rectangle. Each of these instruments has a width along the scraping edge of about 3 ft.

_Triangular and Conical Dredges._--Two other dredges are worthy of mention. The triangular dredge, much resembling Müller's but with a triangular mouth, and hung by chains from its angles, is an old fashion now not in general use. It is, however, very useful for rocky ground. At the Plymouth marine laboratory was also devised the conical dredge (1901), the circular form being the suggestion of Garstang. This dredge (fig. 16) was intended for digging deeply. It is of wrought iron, and of the following dimensions: diameter of mouth 16 in., length 33 in., depth of ring at mouth 9 in. Its weight is 67 lb. As at first used the spaces between the bars are closed by wire netting; if used for collecting bottom samples it is furnished with a lining of strong sail-cloth.

[Illustration: FIG. 16.--Conical Dredge being hoisted in.]

Its weight and the small length of edge in contact with the ground cause this dredge to dig well, and enable the user to obtain many objects which though quite common are of rare occurrence in an ordinary dredge. Thus on the Brown Ridges, a fishing-ground west of Holland, although _Donax vittalus_ is known from examination of fish stomachs to be abundant, it is rarely taken except in the conical dredge: the same is true of _Echinocyamus pusillus_, which is in many parts of the North Sea abundant in bottom samples and in no ordinary dredgings. With the sail-cloth lining the conical dredge fills in about 10 minutes on most ground, and no material washing out of fine sediment occurs on hauling. In shallow seas such as the North Sea commercial beam and other trawls are now used as quantitative instruments in the estimation of the fish population, especially of the _Pleuronectidae_.

_Use of Small Trawls for Dredging._--Although these trawls do not here concern us, certain adaptations of small beam trawls for biological exploration are of such identical use with the dredge, and differ from it so little in structure and size, that they may be here described.

A small beam trawl was first used from the "Challenger" (fig. 17). It was sent down in 600 fathoms off Cape St Vincent, the reason for its use being the frequency with which the dredge sank into the sea-bottom and there remained until hauling. The experiment was entirely successful. The sinking of the net was avoided, the net had a much greater spread than the dredge, and in addition to invertebrates it captured several fish. After this the trawl was frequently used instead of the dredge. Indeed tangle bar, dredge and trawl form a series which are fitted for use on the roughest, moderately rough and fairly firm, and the softest ground respectively, although the dredge can be used almost anywhere.

[Illustration: From Sir Charles Wyville Thomson's _Voyage of the "Challenger."_ By permission of Macmillan & Co., Ltd

FIG. 17.--Trawl of the "Challenger."]

The frame of the "Challenger" trawl consisted of a 15 ft. wooden beam which in use was drawn over the sea-bed on two runners resembling those of a sledge, by means of two ropes or bridles attached to eyes in the front of the runners or "trawl heads." A net 30 ft. long was suspended by one side to the beam by half-a-dozen stops. The remainder of the net's mouth was of much greater length than the beam, and was weighted with close-set rolls of sheet lead; it thus dragged along the bottom in a curve approximately to a semicircle, behind the beam. The net tapers towards the hinder end, and contains a second net with open bottom, which, reaching about three-quarters of the way down the main net, acts as a valve or pocket. Both heels (or hinder ends) of the trawl heads and the tail of the net were weighted to assist the net in digging sufficiently and to maintain its balance--an important point, since if the trawl lands on its beam the net's mouth remains closed, and nothing is caught.

The main differences of this trawl from the dredge are the replacement of scraping lip by ground rope, the position of this ground rope and the greater size of the mouth. The absence of a lip makes it less effective for burrowing and sessile creatures, but the weighted ground rope nevertheless secures them to a very surprising extent. The position of the ground rope is an important feature, as any free swimming creature not disturbed until the arrival of the ground rope cannot escape by simply rising or "striking" up. This and the greater spread make the trawl especially suitable for the collection of fishes and other swiftly moving animals. The first haul of the "Challenger" trawl brought up fishes, and most of our knowledge of fish of the greatest depths is due to it.

A tendency to return to the use of the small beam trawl for deep-sea work has lately shown itself. That used by Tanner on the "Albatross" has runners more heart-shaped than the "Challenger's" instrument; the net is fastened to the downward and backward sloping edge of the runner as well as to the beam, being thus fixed on three sides instead of one; and a Norwegian glass float is fastened in a network cover to that part of the net which is above and in front of the ground rope in use, to assist in keeping the opening clear. These floats can stand the pressure at great depths, and do not become waterlogged as do cork floats. The largest "Albatross" trawl has a beam 11 ft. long, runners 2 ft. 5 in. high, and its frame weighs 275 lb.

_Agassiz or Blake Trawl._--This is generally considered to possess advantages over the preceding, and is decidedly better for those not experts in trawling. Its frame (fig. 18) consists of two iron runners each the shape of a capital letter D, joined by iron rods or pipes which connect the middle of each stroke with the corresponding point on the other letter. The net is a tapering one, its mouth being a strong rope bound with finer rope for protection till the whole reaches a thickness of some 2 in. It is fastened to the frame at four points only, the ends of the curved rods, and thus has a rectangular opening.

[Illustration: From Alexander E. Agassiz's _Three Cruises of the "Blake."_ By permission of Houghton, Mifflin & Co.

FIG. 18.--Agassiz or Blake Trawl.]

The chief advantage of this frame is that it does not matter in the least which side lands first on the bottom; it is to the other trawls what Ball's dredge is to an oyster dredge. The course can also be altered during shooting or towing the Blake trawl with far greater ease than is the case with others. An Agassiz trawl very successful in the North Sea has the following dimensions: length of the connecting rods and therefore of the mouth 8 ft., height of runners and of mouth 1 ft. 9 in., extreme length of runners 2 ft., length of net 11 ft. 3 in., weight of whole trawl 94 lb., 63 of which are due to the frame.

It is instructive to note how closely our knowledge of bottom-living forms has been associated with the instruments of capture in use. As long as small vessels were used in dredging, the belief that life was limited to the regions accessible to them was widely spread. The first known denizens of great depths were the foraminifera and few echinoderms brought up by various sounding apparatus. Next with the dredge and tangles the number of groups obtained was much greater. As soon as trawls were adopted fish began to make their appearance. The greatest gaps in our knowledge still probably occur in the large and swiftly moving forms, such as fish and cephalopods. As we can hardly hope to move apparatus swiftly over the bottom in great depths, the way in which improvement is possible probably is that of increasing the spread of the nets; and a start in this direction appears to have been made by Dr Petersen, who has devised a modified otter sieve which catches fish at all events very well, and has been operated already at considerable depths.

Of the economy of quite shallow seas, however, we are still largely ignorant. Much as has been learnt of the bionomics of the sea, it is but a commencement; and this is of course especially true of deep seas. The dredge and its kindred have, however, in less than a century enabled naturalists to compile an immense mass of knowledge of the structure, development, affinities and distribution of the animals of the sea-bed, and in the most accessible seas to produce enumerations and morphological accounts of them of some approach to completeness. (J. O. B.)

DRELINCOURT, CHARLES (1595-1669), French Protestant divine, was born at Sedan on the 10th of July 1595. In 1618 he undertook the charge of the French Protestant church at Langres, but failed to receive the necessary royal sanction, and early in 1620 he removed to Paris, where he was nominated minister of the Reformed Church at Charenton. He was the author of a large number of works in devotional and polemical theology, several of which had great influence. His _Catechism_ (_Catéchisme ou instruction familière_, 1652) and his _Christian's Defense against the Fears of Death_ (_Consolations de l'âme fidèle contre les frayeurs de la mort, 1651_) became well known in England by means of translations, which were very frequently reprinted. It has been said that Daniel Defoe wrote his fiction of Mrs Veal (_A True Relation of the Apparition of Mrs Veal_), who came from the other world to recommend the perusal of _Drelincourt on Death_, for the express purpose of promoting the sale of an English translation of the _Consolations_; Defoe's contribution is added to the fourth edition of the translation (1706). Another popular work of his was _Les Visites charitables pour toutes sortes de personnes affligées_ (1669). Drelincourt's controversial works were numerous. Directed entirely against Roman Catholicism, they did much to strengthen and consolidate the Protestant party in France. He died on the 3rd of November 1669.

Several of his sons were distinguished as theologians or physicians. Laurent (1626-1681) became a pastor, and was the author of _Sonnets chrétiens sur divers sujets_ (1677); Charles (1633-1697) was professor of physic at the university of Leiden, and physician to the prince of Orange; Peter (1644-1722) was ordained a priest in the Church of England, and became dean of Armagh.

DRENTE, a province of Holland, bounded N. and N.E. by Groningen, S.E. by the Prussian province of Hanover, S. and S.W. by Overysel, and N.W. by Friesland; area, 1128 sq. m.; pop. (1900) 149,551. The province of Drente is a sandy plateau forming the kernel of the surrounding provinces. The soil consists almost entirely of sand and gravel, and is covered with bleak moorland, patches of wood, and fen. This is only varied by the strip of fertile clay and grass-land which is found along the banks of the rivers, and by the areas of high fen in the south-eastern corner and on the western borders near Assen. The surface of the province is a gentle slope from the south-west towards the north-east, where it terminates in the long ridge of hills known as the Hondsrug (Dog's Back) extending along the eastern border into Groningen. The watershed of the province runs from east to west across the middle of the province, along the line of the Orange canal. The southern streams are all collected at two points on the southern borders, namely, at Meppel and Koevorden, whence they communicate with the Zwarte Water and the Vecht respectively by means of the Meppeler Diep and the Koevorden canal. The Steenwyker Aa, however, enters the Zuider Zee independently. The northern rivers all flow into Groningen. The piles of granite rocks somewhat in the shape of cromlechs which are found scattered about this province, and especially along the western edge of the Hondsrug, have long been named _Hunebedden_, from a popular superstition that they were "Huns' beds." Possibly the word originally meant "beds of the dead," or tombs.

Two industries have for centuries been associated with the barren heaths and sodden fens so usually found together on the sand-grounds, namely, the cultivation of buckwheat and peat-digging. The work is conducted on a regular system of fen colonization, the first operation being directed towards the drainage of the country. This is effected by means of drainage canals cut at regular intervals and connected by means of cross ditches. These draining ditches all have their issue in a main drainage canal, along which the transport of the peat and peat-litter takes place and the houses of the colonists are built. The heathlands when sufficiently drained are prepared for cultivation by being cut into sods and burnt. This system appears to have been practised already at the end of the 17th century. After eight years, however, the soil becomes exhausted, and twenty to thirty years are required for its refertilization. The cultivation of buckwheat on these grounds has decreased, and large areas which were formerly thus treated now lie waste. Potatoes, rye, oats, beans and peas are also largely cultivated. In connexion with the cultivation of potatoes, factories are established for making spirits, treacle, potato-meal, and straw-paper. Furthermore, agriculture is everywhere accompanied on the sand-grounds by the rearing of sheep and cattle, which assist in fertilizing the soil. Owing to the meagreness of their food these animals are usually thin and small, but are quickly restored when placed on richer grounds. The breeding of pigs is also widely practised on the sand-grounds, as well as forest culture. Of the fen-colonies in Drente the best known are those of Frederiksoord and Veenhuizen.