Diving Bell.— The most useful of ancient contrivances is the diving bell, which, introduced at an early period and gradually improved, is now the well-known apparatus used by engineers in the present day; and it may be interesting to trace the successive improvements that have brought it to its present state of perfection and usefulness in conducting submarine works.

The conception of the diving bell is very simple. The air contained in an inverted jar sunk in a vessel of water excludes the water from the interior, and if the vessel be made of sufficient size to contain persons within it, it may be sunk without their being wetted, and they may continue to be submerged so long as the air within the bell continues pure enough to support animation. Such were the “divingchests” of the first makers, which, though they differed in form and details, were constructed on the same principle as the modern bell, and were generally formed of wood, girded with iron hoops, like a barrel.

It will be obvious that if such a vessel were submerged in shallow water, having a depth of say one foot of water, a large supply of air would be inclosed in the bell, and the bottom on which it rested would, from the small depth of water upon it, be easily reached for any operation to be performed on it. But if we conceive the same bell to be lowered further below the surface, the air being compressible will be reduced in volume, and the water will rise ir. the bell to fill its place. The result would be that at the depth of about 33 feet the air would be compressed into about one-half its original bulk, and the bell itself would be half filled with water; and the bottom of the sea on which it rested would no longer be so conveniently reached as when the water was only a few inches above the lips of the bell. Moreover, the air by repeated inspiration becomes unfit to support life, and the ancient bells had to be raised to the surface at very short intervals of time that fresh air might be supplied to the men employed. Although, therefore, the original diving bell was a step towards the perfect appliances afterwards introduced, it will readily be seen that its use in diving operations was very limited indeed.

Dr Halley, the secretary of the Royal Society, who seems to have taken an interest in diving and divers, and compassionated their want υf fresh air, communicated a paper to the Royal Society in which, to use his own words, he proposes a plan “for carrying the pabulum vitae down to the divers, who must without being supplied therewith return very soon to the surface or’ perish.” The following is the description of his arrangements for this purpose. After describing the bell itself, which was of wood of the form of a truncated cone, with a capacity of 60 cubic feet, and was suspended by a sprit from the mast of a ship, he says—

“To supply air to this bell when under water, I caused a couple of barrels, of about 36 gallons each, to be cased with lead, so as to sink empty, each of them having a bung-hole in its lowest parts to let in the water, as the air in them condensed on their descent, and to let it out again when they were drawn up full from below. And to a hole in the uppermost part of these barrels I fixed a leathern hose, long enough to fall below the bung-hole, being kept down by a weight appended, so that the air in the upper part of the barrels could not escape, unless the lower ends of these hose were first lifted up.

“The air-barrels being thus prepared, I fitted them with tackle proper to make them rise and fall alternately, after the manner of two buckets in a well; and in their descent they were directed by lines fastened to the under edge of the bell, which passed through rings on both sides of the leathern hose in each barrel, so that, sliding doλvn by these lines, they came readily to the hand of a man, who stood on purpose to receive them, and to take up the ends of the hose into the bell. Through these hose, as soon as their ends came above the surface of the water in the barrels, all the air that was included in the upper parts of them was blown with great force into the bell, whilst the water entered at the bung-holes below and filled them, and as soon as the air of one barrel had been thus received, upon a signal given that was drawn up, and at the same time the other descended, and, by an alternate succession, furnished air so quick, and in so great plenty, that I myself have been one of five who have been together at the bottom, in nine to ten fathoms water, for above an hour and a half at a time, without any sort of ill consequence, and I might have continued there so long as I pleased, for anything that appeared to the contrary. I only observed that it was necessary to be let down gradually at first, at about 12 feet at a time; and then to stop and drive out the air that entered, by receiving 3 or 4 barrels of fresh air before I descended further. But being arrived at the depth designed, I then let out as much of the hot air that had been breathed as each barrel would replenish with cool, by means of the cock at the top of the bell, through whose aperture, though very small, the air would rush with so much violence as to make the surface of the sea boil, and to cover it with a white foam, notwithstanding the weight of the water over us.

“Thus I found that I could do anything that required to be done just under us, and that I could, for a space as wide as the circuit of the bell, lay the bottom of the sea so far dry, as not to be over shoes thereon. And, by the glase window, so much light was transmitted, that when the sea was clear, and especially when the sun shone, I could see perfectly well to write or read, much more to fasten or lay hold on anything under us that was to be taken up; and, by the return of the air barrels, I often sent up orders, written w ith an iron pen on small plates of lead, directing how to move up from place to place as occasion required. At other times when the air was troubled and thick, it would be as dark as night below; but in such cases I have been able to keep a candle burning in the beÚ as long as I pleased, notwithstanding the great expense of air necessarv to maintain flame. This I take to be an invention applicable to various uses, such as fishing for pearls, diving for coral or sponges and the like, in far greater depths than has hitherto been thought possible; also for the fitting and placing of the foundations of moles, bridges, &c., in rocky bottoms, and for cleaning and scrubbing of ships’ bottoms when foul, in cairn weather at sea. I shall only intimate that, by an additional contrivance, I have found it not impracticable for a diver to go out of an engine, to a good distance from it, the air being conveyed to him with a continued stream by small flexible pipes; which pipes may serve as a clue to direct him back again when he would return to the belh”

Such is an account of Dr Halley’s apparatus, which undoubtedly effected an important improvement; but it involved the sending down of constant relays of air vessels, and the great loss of time and interruption which attended such a means of supply. It remained for Smeaton to overcome these objections. In repairing the shoeing of the foundations of Hexham Bridge, in 1778, there being but a small depth of water, to work in, he contrived a bell to the top of which he attached a force pump in lieu of Dr Halley’s air-barrels, and as the bell, in consequence of the small depth of water, did not require to be wholly submerged, the supply of air for the divers was forced directly into the bell, being the first application of the force pump for that purpose. 1 Subsequently to this, in 1748, having occasion to remove stones in clearing the foundations for a pier at Ramsgate, he applied an air-pump placed in a ship or barge, and pumped air into the bell at any depth under water by means of a hose screwed into an air-hole in the top of the bell. The following is Smeaton’s description of his last improvement :—

“Instead of the usual form of a bell, or of a conical tub of wood sunk by weights (externally applied), this for convenience was a square chest of cast iron, which being 50 cwts. was heavy enough to sink itself, and being 4⅛ feet in height, 4⅜ feet in length, and 3 feet wide, afforded room sufficient for two men at a time to work under it. But it was peculiar to this machine that the men therein were supplied with a constant influx of fresh air without any attention of theirs, that necessary article being amply supplied by »forcing air-pump in a boat upon the water’s surface.” a

It will thus be seen that Smeaton’s Ramsgate bell contained all the elements of the present appliances, which, as improved in details, and constructed by Messrs Rennie, has been so extensively employed in harbour works.

The bell as now used is shown in plan and section in figs. 1 and 2. It is a cast-iron chest weighing about 5 tons, and is suspended by block and tackle.

On the top of the bell there are 8 apertures α, fitted with very thick glass for admitting light; and in the centre is the passage δ, into which the hose is screwed for admitting the air supply. The interior is fitted with two seats e, which can be removed to make room when the men are at work; and in the centre is a lifting chain c, to which stones are attached to facilitate their being lifted and properly adjusted to the beds on which they are to be laid. The bell is used according to two different systems, depending on the nature of the work to be performed. In building masonry under water it is suspended from a staging of timber, but in excavating rock or removing boulders, scattered over a considerable area, where a staging would be inapplicable, it is suspended from a barge or lighter.

Fig. 3 shows the arrangement as employed in laying Bell-stones or blocks of concrete. It represents a cross section staging, of the staging, bell framing, and bell carriage, in which a is the staging, δ longitudinal beams on which the bellframing cc traverses on the wheels and toothed racks d. The diving bell e is suspended from the bell carriage/, which traverses on the bell framing by the wheels and toothed rack g across the whole breadth of the pier. The stones h, are brought along the surface of the finished part of the pier, and lowered down by the travelling crab-winch I. The force-pumps by which the bell is supplied with air are shown at m, and the air-hose at n. It will be understood from this description that the bell framing c, moves freely along the staging, while the bell carriage has a 1 Smeaton’s Reports, vol. iii. p. 279.

α Historical Report on Ramsgate Harbour, by John Smeaton, London 1791, p. 70.

motion at right angles across the work, so that the position of the bell· can be altered with the greatest ease so as to bring it over any spot within the area of the staging.

In proceeding to work, the men take their seats in the bell from a boat, and the bell is then lowered to the required depth. If the work be that of building a wall a stone is lowered at the same time. The changes in the position of the bell are all made according to signs given by the divers by strokes of a hammer on the bell, which experience has shown can be heard at any depth at which the diving bell has been employed. The signals are— one stroke, more air; two, hold on; three, raise; four, lower ∙,five, north; six, south; seven, east; eight, west. These signals are narrowly observed by a watchman stationed in a boat, and reported to the men working the bell carriage. The rule for the supply of air both to the bell and diving dress is to give it so freely that there shall be a constant escape of air rising to the surface in air-bubbles all the time the men are under water. After being lowered, the bell is first moved over the stone to be laid; the divers then unhook the lowering chain from the lewis in the stone, and at the same time make fast the stone to the tackle within the bell, which is at once signalled to be raised, andL carries the stone with it. The bell is then moved over the site on which it is to be placed; it is then lowered until it has nearly reached its bed, on which it is finally deposited. The lewis is then removed and the bell raised for another stone; and with trained workmen it is surprising how expeditiously the bell is moved from place to place, and stone after stone is built in the walls. The staff of men required to work the bell is two divers, one watchman, four men working the air-pump, and four working the bell carriage, besides the men required to bring forward and send down the stones. The men engaged generally work in shifts of from 3 to 6 hours according to the depth, and the diving work may be continued as long as in ordinary day-work, as in clear water the light is good to the greatest depth at which the bell is used in harbour building.

When engaged in blasting, the bore is made in the ordinary way, and charged with a shot inclosed in a water-tight canvas case, to which is attached a length of 6 or 8 feet of patent fuse. The bell is then moved from above the bore, and the fuse ignited, and when the shot is fired the smoke rises to the surface clear of the bell.

When employed for removing rock or boulder stones—for example, in a river navigation,—it is of advantage that the bell be capable of being easily transported, and in that case it is swung from a barge or lighter, which contains the machinery for w orking the bell and air-pumps, and a crane for raising tħe boulders as the divers sling them. It is of course attended with greater trouble and risk to the divers to work the bell from a lighter than from a stage; but, on the other hand, the convenience in being enabled to trans port it from place to place, in a river navigation, is a great advantage.

Figs. 4 and 5 show the disposition of the various appliances in the most recent bell-lighter built by Messrs Simons of Renfrew for the River Clyde, which was communicated by Mr Deas, the engineer, to the Clyde Trustees. Fig. 4 is a longitudinal section, and fig. 5 a plan in which a is the bell, b the bell crab, c the air-pumps, and d the crane for lifting stones, &c., slung by the divers.

The large cost of a diving bell limits its use to works of magnitudo, especially as many submarine works can be done better by the diving dress, which is much less expensive; but there are certain operations, such as the clearing and levelling of foundations, for which the bell is peculiarly well adapted, that still enable it to take its place as one of the most useful appliances of the marine engineer. Mr B. B. Stoney has, in an interesting paper in the Minutes of Proceedings of the Institution of Civil Engineers, described a diving bell, or chamber, 20 feet square, with which he successfully built the foundation of the quays of Dublin. Mr Stoney’s apparatus does not come under the article diving, but belongs more properly to the subject of the compressed air cylinders used in bridge building, which are described under the article Bridge. Diving Dress.— The diving dress is peculiarly well fitted for such worksas the repair or overhaul of rollers and sluices of lock-gates, cleaning or repairing ships’ bottoms, descending into the hatches of wrecks to recover property, and, in short, everything that cannot be done from the interior of a bell. The inexpensiveness also of the diving dress, dispensing with all costly staging, and its ease of transport and appliance, are much in favour of its use. It is, indeed, so convenient in the repair of propellers, examining ships’ bottoms, recovering anchors, <fcc., that all ships in Her Majesty’s navy of sufficient size to be commanded by captains are now supplied with a diving dress or apparatus, and bear a certain number of divers in their complements; and all sea-going flagships and iron clads on foreign stations carry two sets of diving apparatus, and are allowed a suitable number of trained divers.

The invention of the diving dress, like that of most useful appliances, was gradual, and the work of many minds. Some early proposals, such as that already referred to in the quotation from Dr Halley’s paper in 1721, and others of more modern date, were made for providing the diver with a dress to enable him with safety to carry on his work, for an account of which the reader is referred to a paper by Mr J. W. Heinke in the Minutes of Proceedings of the Institution of Civil Engineers. But to Mr A. Siebe is due the credit of being the first to introduce a dress which was supplied with a constant stream of fresh air, and may be said to have been the precursor of the dress now in use. We allude to what was called the “open dress” invented in 1829, which consisted of a helmet and waterproof jacket, under which, and fitting more closely to the body, were worn trousers reaching to the arm pits, and between the jacket and trousers the air pumped in at the helmet was allowed to force its way and escape to the surface as in the diving bell, and hence it was called “open.” Although some divers of the old school are said still to give a preference to the open dress, its danger became manifest; for if a diver stumbled...