Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/313

DIVING 295 shoes thereon. And, by the glass 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 with 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 bell as long as I pleased, notwithstanding the great expense of air necessary to maintain flame. This I take to be an invention appli cable 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 found ations of moles, bridges, &c., in rocky bottoms, and for cleaning and scrubbing of ships bottoms when foul, in calm 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 i rom 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 bell." leaton s Such is an account of Dr Halley s apparatus, which un- ring-bell. doiibtedly 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 sub merged, 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 r,unk 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 4^ feet in height, 4^ 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 there in 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." 2 >lern It will thus be seen that Smeaton s Ramsgate bell con- niig bell tained 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 a, fitted with very thick glass for admit ting light ; and in the centre is the passage 6, 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 1 Smeaton s Reports, Tol. iii. p. 279. 3 Historical Report on Ramsgate Harbour, by John Smeaton, London 1791, p. 70. Fio. 1. Plan of Diving Bell. nature of the work to be performed. In building masonry under water it is suspended from a staging of timber, but in excavatiug rock or removing boulders, scattered over FIG. 2. Section of Diving Bell. 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 Fro. 3. Block-laying by Diving Bell. is the staging, b longitudinal beams on which the bell- framing 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 in, and the air-hose at n. It will be under stood from this description that the bell framing c, moves

freely along the staging, while the bell carriage has a