Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/314

296 DIVING 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. Tn 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, Bast ; 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 BO 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, and. 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 w r ay, 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 f or removing rock or boulder stones for FIG. 4. Longitudinal Section of Diving Bell Lighter (56 feet long and 24 feet beam). 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 working the bell and air-pumps, and a crane for raising the 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- Pia. 5. Plan of Bell Lighter (56 feet long and 24 feet beam). 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