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DIVERS and DIVING APPARATUS. To " dive " (Old Eng. (Wan, dyfan; cf. "See also:dip") is to plunge under See also:water, and in the See also:ordinary See also:procedure of swimmers is distinguished from See also:simple plunging in that it involves remaining under the water for an See also:interval of more or less duration before coming to the See also:surface. In. the See also:article See also:SWIMMING the See also:sport of diving in this sense is considered. Here we are only concerned with diving as the See also:function of a " See also:diver," whose business it is to go under water (in See also:modern times, assisted by specially devised apparatus) in See also:order to See also:work.
Unassisted or Natural Diving.—The earliest reference to the practice of the See also:art of diving for a purpose of utility occurs in the Iliad, 16, 745–750, where Patroclus compares the fall of See also:Hector's charioteer to the See also:action of a diver diving for oysters. Thus it would seem that the art was known about loco years before the See also:Christian era. See also:Thucydides is the first to mention the employment of divers for See also:mechanical work under water. He relates that divers were employed during the See also:siege of See also:Syracuse to saw down the barriers which had been constructed below the surface of the water with the See also:object of obstructing and damaging any Grecian See also:war vessels which might See also:attempt to enter the See also:harbour. At the siege of See also:Tyre, divers were ordered by See also: The employment of divers for the See also:salvage of sunken See also:property is first mentioned by See also:Livy, who records that in the reign of See also:Perseus considerable treasure was recovered from the See also:sea. By a See also:law of the Rhodians, their divers were allowed a proportion of the value recovered, varying with the See also:risk incurred, or the See also:depth from which the treasure was salved. For instance, if the diver raised it from a depth of eight cubits (12 ft.) he received one-third for himself; if from sixteen cubits (24 ft.) one See also:half; but upon goods lost near the See also:shore, and recovered from a depth of two cubits (36 in.), his See also:share was only one tenth. These are examples of unassisted diving as practised by the Ancients. Their See also:primitive method, however, is still in See also:vogue in some parts of the world—notably in the See also:Ceylon See also:pearl See also:fisheries and in the Mediterranean sponge fisheries, and it may, therefore, be as well to mention the See also:system adopted by the natural, or naked, diver of to-day. The See also:volume and See also:power of respiration of the lungs vary in different individuals, some persons being able to hold their breath longer than others, so that it naturally follows that one See also:man may be able to stay longer under water than another. The longest See also:time that a natural diver has been known to remain beneath the surface is about two minutes. Some pearl and sponge divers rub * See also:Lawrence's C. pacificus seems hardly to deserve specific recognition. 6 In this connexion should be mentioned the remarkable occurrence in See also:Europe of two birds of this See also:species which had been previously wounded by a weapon presumably of transatlantic origin. One had " an arrow headed with See also:copper sticking through its See also:neck," and was shot on the Irish See also:coast, as recorded by J. See also:Vaughan See also:Thompson (Nat. Hist. See also:Ireland, iii. p. sot); the other, says Herr H. C. See also: See also:Early Diving Appliances.—The earliest mention of any appliance for assisting divers is by See also:Aristotle, who says that divers are sometimes provided with See also:instruments for respiration through which they can draw See also:air from above the water and which thus enable them to remain a See also:long time under the sea (De Fart. Anim. 2, 16), and also that divers breathe by letting down a metallic See also:vessel which does not get filled with water but retains the air within it (Problem. 32, 5). It is also recorded that Alexander the Great made a descent into the sea in a See also:machine called a colimpha, which had the power of keeping a man dry, and at the same time of admitting See also:light. See also:Pliny also speaks of divers engaged in the See also:strategy of See also:ancient warfare, who See also:drew air through a See also:tube, one end of which they carried in their mouths, whilst the other end was made to See also:float on the surface of the water. See also:Roger See also: For this purpose he used a large pair of See also:bellows. See also: The helmet was fitted with an air inlet See also:valve, to which one end of a flexible tube was attached, the other end being connected at the surface with a pump which supplied the diver with a See also:constant stream of fresh air. The air, which kept the water well down, forced its way between the jacket and the under-garment; and escaped to the surface on exactly the same principle as that of the diving See also:bell; hence the See also:term " open " as applied to this dress. Although most excellent work was accomplished with this dress —work which could not be attempted before its introduction—it was still far from perfect. It was absolutely necessary for the diver to maintain an upright, or but very slightly stooping, position whilst under water; if he stumbled and See also:fell, the water filled his dress, and, unless quickly brought to the surface, he was in danger of being drowned. To overcome this and other defects, Siebe carried out a large number of experiments extending over several years, which culminated, in the year 1830, in the introduction of his " See also:close " dress in combination with a helmet fitted with air inlet and regulating outlet valves. Though, of course, vast improvements have been introduced since Siebe's See also:death, in 1872, the fact remains that his principle is in universal use to this day. The submarine work which it has been instrumental in accomplishing is incalculable. But some See also:idea of the importance of the invention may be gathered from the fact that diving apparatus on Siebe's principle is universally used to-day in harbour, See also:dock, See also:pier and See also:breakwater construction, in the pearl and, sponge fisheries, in recovering sunken See also:ships, cargo and treasure, and that every See also:ship in the British See also:navy and in most See also:foreign navies carries one set or more of diving apparatus. A modern set of diving apparatus consists essentially of six parts:—(1) an air pump, (2) a helmet with breastplate, (3) diving dress, (4) a pair of heavily weighted boots, (5) a pair of back and chest weights, (6) a flexible non-collapsible air tube. Air Pumps.—The type of air pump varies with the depth of water to which the diver has to descend; it will be readily understood that the greater the depth the greater the quantity of air required by the diver. The pat-See also:tern most generally in favour amongst divers of all classes is a three - cylinder single-acting pump, which is suitable for almost every description of work which the diver may be called upon to perform, either in deep or shallow water. Another most useful type is a two-cylinder See also:double-acting pump (See also:figs. 1 and 2), which is designed to supply two divers working simultaneously in moderate depths of water, or one diver only in deep water. An air-distributing arrangement is fitted, whereby, when it is desired to send two men A, Air-distributing ar- D, Cylinders. rangement, for one E, Pressure gauges. diver or two divers. F, Nozzles to which B, Water jacket. divers' air pipes C, Suction and dis- are attached. See also:charge valves. down together, each cylinder supplies air independently of the other; and when it is required to send one diver into deep water, the two cylinders are connected and the full volume of air from both is delivered to the one man. The same See also:duty is also performed by a four-cylinder single-acting pump. Smaller pumps, having one double-acting or two single-acting cylinders, are also used for shallow water work. In most cases these air pumps are worked by See also:manual power; this method• of working is rendered necessary by the fact that the See also:machines are usually placed in small boats from which the divers work and on which other See also:motive power is not available. In cases, however, where See also:steam or electric power is available the pumps are sometimes worked by their means—more particularly on harbour and dock See also:works. In such instances the air is not delivered See also:direct from the pump to the diver, but is delivered into an intermediate See also:steel See also:receiver to which the diver's air pipe is connected, the object being to ensure a reserve supply of air in case of a breakdown of the pump. Some of these combinations of pumps and See also:motors are so arranged that, in the event of an See also:accident to the motor, the pump can be thrown out of gear with it, and be immediately worked by See also:hand power. Each pump is fitted with a See also:gauge (or gauges), indicating not only the pressure of air which the pump is supplying, but also the depth of water at which the diver is working. The cylinders are water-jacketed to ensure the air delivered to the diver being cool, the water being drawn in and circulated See also:round the cylinders by means of a small metal pump worked from an See also:eccentric on the See also:main See also:crank-See also:shaft. Filters are sometimes attached to the suction and delivery sides of the pumps to ensure the inlet of air being free from dirt, and the See also:discharge of air free from dirt and oil. Helmet.—The helmet and breastplate (fig. 3) are made from highly planished tinned copper, with See also:gun-metal valves and other fittings. The helmet is provided with a non-return air inlet valve to which the diver's air pipe is connected; the air when it lifts the inlet valve passes through three conduits—one having its outlet over the front See also:glass, the others their outlets over the See also:side glasses. In this way the diver gets the air fresh as it enters the helmet, and at the same time it prevents condensation of his breath on the glasses and keeps them clear. There is a regulating air outlet valve by which the diver adjusts his supply of air according to his requirements in different depths of water; the valve is usually made to be adjusted by hand, but sometimes it is so constructed as to be operated by the diver knocking his head against it, the spindle being extended through to the inside of the helmet and fitted at its inner extremity with a See also:button or disk. By unscrewing the valve, the diver allows air to escape, and thus the dress is deflated; by screwing it up the air is retained and the dress inflated. Thus the diver can See also:control his specific gravity and rise or sink at will. In case by any See also:chance the diver should inflate the dress inadvertently, and wish to get rid of the superfluous air quickly, he can do so by opening an emergency See also:cock, which is fitted on the helmet. Plate glasses in gun-metal frames are also fitted to the helmet, two, one on each side, being permanently fixed, while one in front is made either to See also:screw in and out, or to work on a hinged See also:joint like a ship's See also:scuttle; the side glasses are usually protected by metal See also:cross-bars, as is also sometimes the front glass. Some divers prefer unprotected• glasses at the side of the helmet, instead of protected See also:oval ones. The breastplate is fitted on its See also:outer edge with metal screws and bands. The disposition of the screws corresponds with that of the holes in the See also:india-See also:rubber See also:collar of the diving dress described below. There are other methods of making a watertight joint between the diver's breastplate and the diving dress, but, as these are only mechanical See also:differences, it will suffice to describe the Siebe-Gorman apparatus, as exclusively adopted by the British See also:government. Whatever the shape or See also:design of the helmet or dress, Siebe's principle is the one in universal use to-day. The metal tabs are for carrying the diver's See also:lead weights, which are fitted with suitable clips; the hooks—one on each side of the helmet —are for keeping the See also:ropes attached to the back See also:weight in position. The helmet and breastplate are fitted at their See also:lower and upper parts respectively with gun-metal segmental neck rings, which make it possible to connect these two main parts together by one-eighth of a turn, a catch at the back of the helmet preventing any chance of unscrewing. The small eyes at the See also:top of the helmet are for securing the diver's air pipe and See also:life See also:line in position and preventing them from swaying. Front view of Helmet. A, Helmet. B, Breastplate. F, Emergency cock. G, Glasses in frames. H, Metal screws and bands. I, 'Metal tabs. J, Hooks for keeping weight ropes in position. L, Eyes to which air pipe and life line are secured. See also:Plan of Helmet. C, Air inlet valve. E, Regulating outlet valve. G, Glasses in frames. L, Eyes to which air pipe and life line are secured. P, Connexion for See also:telephone See also:cable. The Diving Dress is a combination suit which envelops the whole body from feet to neck. It is made of two layers of tanned See also:twill with pure rubber between, and is fitted at the neck with a vulcanized India-rubber collar, or See also:band, with holes punched in it corresponding to the screws in the breastplate. This collar, when clamped tightly between the bands and the breastplate by means of the nuts, ensures a watertight joint. The sleeves of the dress are fitted with vulcanized india-rubber cuffs, which,, fitting tightly round the diver's wrists, prevent the See also:ingress of water at these parts also. Boots.—These are generally made with leather uppers, beechwood inner soles and leaden outer soles, the latter being secured to the others by copper rivets. Heavy leather straps with See also:brass buckles secure the See also:boot to the See also:foot. Each boot weighs about 16 lb. Sometimes the main See also:part of the boot-See also:golosh, toe and See also:heel, are in one brass casting, with leather upper part, heavy straps and brass buckles. Lead Weights.—These weigh 40 lb each, and the diver wears one on his back, another on his chest. These weights and the heavy boots ensure the diver's See also:equilibrium when under water. See also:Belt and See also:Knife and Small Tools.—Every diver wears a heavy See also:waist-belt in which he carries a strong knife in metal case, and some-times other small tools. Air .Pipe.—The diver's air pipe is of a flexible, non-collapsible description, being made of alternate layers of strong See also:canvas and vulcanized india-rubber, with steel or hard drawn metal See also:wire em-bedded. At the ends are fitted gun-metal couplings, for connecting the pipe with the diver's pump and helmet. Back view of Helmet. Side sectional view of Helmet. K, Segmental neck rings. D, Air conduits. M, Telephone receiver. N, Transmitter. 0, Contact piece to See also:ring bell. See also:Signal Line.—The diver's signal line (sometimes called life line) consists of a length of See also:reverse laid See also:Manila rope. In cases where the telephone apparatus is not used, the diver gives his.signals by means of a See also:series of pulls on the signal line in accordance with a prearranged See also:code. Telephonic Apparatus.—Without doubt one of the most useful adjuncts to the modern diving apparatus is the loud-See also:sounding telephone (fig. 4), introduced by Siebe, Gorman & Co., which enables the diver to communicate viva voce with his attendant, and See also:vice versa. In the British navy the type of submarine telephonic apparatus used is the See also:Graham-See also:Davis system. This is made on two plans, (I) a single set of instruments, for communication between one diver and his attendant direct, (2) an intercommunication set which is used where two divers are employed. With this type the attendant can speak to No. i or No. 2 diver separately, or with both at the same time, and vice versa; and No. i can be put in communication with No. 2 whilst they are under water, the attendant at the surface being able to hear what the men are saying. The advantages of such a system are obvious. It is more particularly useful where two divers are working one either side of a ship, or where the divers may be engaged upon the same piece of work, but out of sight of one another, or out of See also:touch. It would prove its utility in a marked degree in cases where a diver got into difficulties; a second diver sent down to his assistance could receive and give verbal directions and thus greatly expedite the work of See also:rescue. The telephone instruments In the helmet consist of one or more loud-sounding receivers placed either in the See also:crown of the helmet, or one on each side in close proximity to the diver's ears. A transmitter of a See also:special watertight See also:pattern is placed between the front glass and one of the side glasses, and a contact piece, which, when the diver presses his See also:chin against it, rings a bell at the surface, is fitted immediately below the front glass. A buzzer is sometimes fixed in the helmet to See also:call the diver's See also:attention when the attendant wishes to speak, but as a See also:rule the See also:voice is transmitted so loudly that this See also:device is unnecessary. A connexion, through which the insulated wires connecting the instruments pass, terminates in contact pieces, and the telephone cable, embedded in the diver's signal line, is connected with it. The other end of the signal line is connected to a See also:battery See also:box at the surface. This box contains, besides the cells, a receiver and transmitter for the attendant, an electric bell, a terminal box, and a special switch, by means of which various communications between diver, or divers, and attend-See also:ant are made. If, as is sometimes the case, the diver hap-pens to be somewhat See also:deaf, he can, whilst he is taking a See also:message, stop the vibration of the outlet valve and the See also:noise made by the escaping air, by merely pressing his See also:finger on a spindle which passes through the disk of the valve, and thus momentarily ensure See also:absolute silence. Speaking Tube.—The rubber speaking tube which was the fore-runner of the telephonic apparatus is now practically obsolete, though it is still used in isolated cases. Submarine Electric Lamps.—Various forms of submarine lamps are used, from a powerful arc light to a self-contained hand See also:lamp, the former giving about 2000 or 3000 See also:candle-power, and requiring a steam-driven See also:dynamo to supply the necessary current, the latter (fig. 5) giving a light of about 10 candle-power and having its own batteries, so that the diver carries both the light and its source in his hand. These submarine lamps are all constructed on the same principle, having the incandescent lamps, or carbons as the case may be, enclosed in a strong glass globe, the mechanism and connexions being fitted in a metal case above the globe, which is flanged and secured watertightly to the case. Self-contained Diving Dress.—The object of the self-contained diving dress is to make the diver See also:independent of air supply from the surface. The dress, helmet, boots and weights are of the ordinary pattern already described, but instead of obtaining his air supply by means of pumps and pipes, the diver is equipped with a knapsack consisting of a steel cylinder containing See also:oxygen compressed to a pressure of 120 atmospheres (=about 180o lb) to the square See also:inch, and See also:chambers containing See also:caustic soda or caustic potash. The helmet is connected to the chambers by tubes, and the oxygencylinder is similarly connected to the chambers. The breath exhaled by the diver passes through a valve into the caustic soda, which absorbs the carbonic See also:acid, and it is then again inhaled through another valve. This See also:process of regeneration goes on automatically, the requisite amount of oxygen being restored to the breathed air in its passage through the chambers. This type of apparatus has been used for shallow water work, but the great See also:majority of divers prefer the apparatus using pumps as the source of the air supply. An emergency dress, using this self-contained system for breathing, has been designed by Messrs Fleuss and Davis, of the firm of Siebe, Gorman & Co., primarily as a life-saving apparatus, for enabling men to escape from disabled submarine boats. The helmet diver is indispensable in connexion with harbour and dock construction, See also:bridge-See also:building, pearl and sponge fishing, See also:wreck Reflector. A, Metal case containing C, Stand, which also See also:pro-
See also:electrical fittings. tects the globe.
B, Glass globe and incan- D, Ring for suspending lamp.
descent lamp. E, Reflector.
raising and the recovery of sunken cargo and treasure. Every ship in the British navy carries one set or more of diving apparatus, for use in case of emergency, for clearing fouled propellers, cleaning valves or ship's See also:hull below the water line, repairing hulls if necessary, and recovering lost anchors, chains, torpedoes, &c.
Greatest Depths attained.—The greatest depth at which useful' work has been performed by a diver is 182 ft. From this depth a See also:Spanish diver, See also:Angel Erostarbe, recovered £9000 in See also:silver bars from the wreck of the steamer " Skyro," sunk off Cape Finisterre; Alexander See also:Lambert succeeded in salving £70,000 from the Spanish See also:mail steamer " See also:Alphonso XII," sunk in 162 ft. of water off See also:Las Palmas, See also:Grand See also:Canary; W. Ridyard recovered £50,000 in silver dollars from the " See also: The weighted tools employed by divers differ very little from those used by the workmen on terra firma. Pneumatic tools, worked by compressed air conveyed from the surface through flexible tubes, are great See also:aids, particularly in See also:rock removal work. With the rock See also:drill the diver bores a number of holes to a given depth, inserts in these the charges of See also:dynamite or other explosive used, attaches one end of a wire to a detonator which is inserted in the charge, and then comes to the surface. The boat from which he works is then moved away from the See also:scene of operations, paying out the wire attached to the detonators, and when at a safe distance the free end of the wire is connected to a magneto exploding machine, which is then set in See also:motion. A See also:complete set of diving apparatus See also:costs from £75 to £200, varying with the depth of water for which it is required. The pay of a diver depends upon the nature of the work upon which he is engaged, and also upon the depth of the water. On harbour and dock work the See also:average wage is 2s. to 2s. 6d. per See also:hour; on wreck work from 3s. to 5s. an hour, according to depth; on, treasure and cargo recovery so much per day, with a percentage on the value recovered, generally about 5 %. The pearl fishers of Australia get so much per ton of See also:shell, and the sponge fishers are also paid by results. . with the Surface. Q, Battery, with switch and bell in case. R, Attendant's receiver and transmitter. A problem which has been exercising the minds of those engaged in submarine work is the greatest depth at which it is possible to work, for, as is well known, many a See also:fine vessel with valuable cargo and treasure is lying out of reach of the diver owing to the pressure which he would have to sustain were he to attempt to reach her. Mr Leonard See also: Pressure.
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If a diving bell be sunk to a depth of, say, 33 ft., the air inside it will be compressed to about half its See also:original volume, and the bell itself will be about half filled with water. But if a supply of air be maintained at a pressure equal to the depth of water at which the bell is submerged, not only will the water be kept down to the cutting edge, but the bell will be ventilated and it will be possible for its occupants to work for See also:hours at a stretch.
Tradition gives Roger Bacon, in 1250, the See also:credit for being the originator of the diving bell, but actual records are lost in antiquity. Of the records preserved to us, probably one of the most trustworthy is an See also:account given in Kaspar Schott's work, Technica curiosa, published in the year 1664, which quoted from one John Taisnier, who was in the service of See also: See also:Francis Bacon, in the Novum Organum, See also:lib. ii., makes the following reference to a machine, or See also:reservoir, of air to which labourers upon wrecks might resort whenever they required to take breath: ” A hollow vessel, made of metal, was let down equally to the surface of the water, and thus carried with it to the bottom of the sea the whole of the air which it contained. It stood upon three feet—like a tripod—which were in length something less than the height of a man, so that the diver, when he was no longer able to contain his breath, could put his head into the vessel, and having filled his lungs again, return to his work.” But it was to Dr See also:Edmund See also:Halley, secretary of the Royal Society, that undoubtedly the See also:honour is due of having invented the first really practical diving bell. This is described in the Philosophical Transactions, 1717, in a See also:paper on " The Art of Living Under Water by means of furnishing air at the bottom of the sea in any ordinary depth." Halley's bell was constructed of See also:wood, and was covered with lead, which gave it the necessary sinking weight, and was so distributed as to ensure that it kept a perpendicular position when in the water. It was in the See also:form of a truncated See also:cone, 3 ft. in See also:diameter at the top, 5 ft. at the bottom and 8 ft. high. In the roof a See also:lens was introduced for admitting light, and also a tap to let out the vitiated air. Fresh air was supplied to the bell by means of two lead-lined barrels,each having a bung-hole in the top and bottom. To the hole in the top was fixed a leathern tube, weighted in such a manner that it always fell below the level of the bottom of the See also:barrel so that no air could escape. When, however, the tube was turned up by the attendant in the bell, the pressure of the water rising through the hole in the bottom of the barrel, forced the air through the tube at the top and into the diving bell. These barrels were raised and lowered alternately, with such success that Halley says that he, with four others, remained at the bottom of the sea, at a depth of 9 to 10 fathoms, for an hour and a half at a time without inconvenience of any sort. This type of bell was used by John See also:Smeaton in repairing the See also:foundations of See also:Hexham Bridge in 1778, but instead of weighted barrels, he introduced a force pump for supplying the necessary air. To Smeaton too we are indebted for the first diving bell plant in the form with which we are familiar to-day, that celebrated engineer having designed a square bell of iron, for use on the See also:Ramsgate harbour works, in 1788. This bell, which measured 4i ft. in length, 3 ft. in width and 4 ft. in height, and weighed 2i tons, was made sufficiently heavy to sink by its own weight. It afforded See also:room enough for two men to work, and was supplied with air by a force pump worked from a boat at the surface. Though the diving bell has been largely superseded by the modern diving apparatus, it is still used on certain classes of work the magnitude of which justifies the expense entailed, for it is not only a question of the cost of the bell, but of the powerful steam-driven See also:crane which is needed to lower and raise it, and also of the gantry on which the crane travels. Sometimes a See also:barge or other vessel is used for working the bell. At the See also:present day, two types of diving bell are employed—the ordinary bell, and the air-See also:lock bell, which, however, is not so largely used. On the new See also:national harbour works at See also:Dover, four large diving bells of the ordinary type (fig. 6) were employed. These bells, in each of which from four to six men descended at a time, consisted of steel chambers, open at the bottom, measuring 17 ft. long by 10 ft. wide by 7 ft. high, and each weighed 35 tons. The See also:ballast, which at once gives the necessary sinking weight to the bell and maintains its equilibrium, consisted of slabs of See also:cast iron bolted to the walls of the bell, inside. Each bell was fitted with loud-sounding telephonic apparatus; by means of which the occupants could communicate either with the men attending the crane or the men looking after the air compressors at the surface. Electric lamps, supplied with current by a dynamo in the See also:compressor room, gave the necessary light inside the bell. Seats and foot rails were provided for the men, and there were racks and hooks for the various tools. Suspended from the roof was an iron skip into which the men threw the excavated material, which was emptied out when the bell was brought to the surface. Air was supplied to the bells by means of steam-driven compressors worked in a See also:house erected on the gantry. The air was delivered into a steel air receiver, and thence it passed through a flexible tube connected to a gun-metal inlet valve in the roof of the diving bell ; the pressure of air was regulated according to the depth at which the bell happened to be working. The maximum depth on the Dover works was between 6o and 70 ft., =about 25-30 lb to the square inch. A bell was lowered by means of powerful steam-driven See also:cranes, travelling on a gantry, to within a few feet of the water, and the men entered it from a boat. The bell then continued its descent to the bottom, where the men, with pick and See also:shovel, levelled the sea See also:bed ready to receive the large See also:concrete blocks, weighing from 1 1 I F. t See also:ICI i Fig. 7.—Air-lock Diving Bell. A, Working chamber. E, Tackles suspended from roof B, Air-lock. for raising and lowering C, Pulleys and wire ropes for See also:objects. lowering and raising bell. F, Air supply pipe. D, Iron See also:ladder. 30 to 42 tons apiece. Having completed one See also:section, the bell was moved along to another. The concrete blocks were then lowered and placed in position by helmet divers. The bell divers, clad in thick woollen suits and watertight thigh boots, worked in shifts of about three hours each, and were paid at the See also:rate of from Is. to 15d. per hour. The cost of an ordinary diving bell, including air compressor, telephonic apparatus and electric light, is from £60o to £1500, according to See also:size. The Air-lock Diving Bell (fig. 7) comprises an iron or steel working chamber similar to the ordinary diving bell, but with the addition of a shaft attached to its roof. At the upper end of the shaft is an air-tight See also:door, and about 8 ft. below this is another similar door. When the bell divers wish to enter the bell, they pass through the first door and close it after them, and then open a cock or. valve and gradually let into the space between the two doors compressed air from the working chamber in order to equalize the pressure; they then open the second door and pass down into the working chamber,closing the door after them. When returning to the surface they reverse the operation. It can readily be imagined that, owing to its unwieldy See also:character, the employment of the air-lock bell is resorted to only in those cases where the nature of the sea bed necessitates its remaining on a given spot for some considerable time, as for instance in the excavation of hard rock to a given depth. An air-lock bell supplied to the British Admiralty, for use in connexion with the laying of moorings at See also:Gibraltar, has a•working chamber measuring 15 ft. long by See also:io2 ft. wide, by 71 ft. high, and a shaft 37- ft. high by 3 ft. in diameter. It is built of steel plates, with cast-iron ballast, and its See also:total weight is about 46 tons. . The bell is electrically lighted, and is fitted with telephonic apparatus communicating with the air-compressor room and lifting-winch room. It is worked through a well in the centre of a specially constructed steel barge 85 ft. long by 40 ft. See also:beam, having a See also:draught of 7 ft. 6 in. The wire ropes, for lowering and raising the bell, work over pulleys which are carried on a superstructure erected over the well. Two sets of air compressors are fitted on the barge—one set for supplying air to the bell, the other set for working a pneumatic rock drill inside the bell. The greatest depth at which this particular bell will work is 40 ft. The cost of the whole plant, including barge, was about £14,000. The diving dress has, however, to a great extent supplanted the diving bell. This is due not only to the heavier cost of the latter, but more particularly to the greater mobility of the helmet diver. Bell divers are naturally limited to the See also:area which their bell for the time being covers, whereas helmet divers can be distributed over different parts of a See also:contract and work entirely independently of one another. The use of the diving bell is, therefore, practically limited to the work of levelling the sea bed, and the removal of rock. See also the article See also:CAISSON DISEASE as regards the physiological effects of compressed air. (R. H. D.*)
DIVES-SUR-MER, a small See also:port and seaside resort of See also:north-western See also:France on the coast of the See also:department of See also:Calvados, on the Dives, 15 M. N.E. of See also:Caen by road. Pop. (1906) 3286. Dives is celebrated as the harbour whence See also: Additional information and CommentsThere are no comments yet for this article.
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