DIVING, plunging into water and remain ing submerged for greater or less periods of time, with or without communication with the atmospheric air. Diving without the aid of some artificial means to supply the diver with air under water is now rarely practised (unless for amusement) except in sponge, coral and pearl fishing, and sometimes for recovering treasure from wrecked vessels. The best divers are able to remain about one minute and a third under water, and only in extreme and excep tional cases as long as two minutes. Instances are recorded of divers remaining four, five and even six minutes under water, but these are of questionable authenticity.
To enable divers to remain for a consider able time (sometimes five or six hours) under water a diving dress has been used, which is so contrived that the diver is constantly supplied with air from above. It consists of a water proof dress, to which is attached a neck-piece or breast-plate fitted with a segmental screw bayonet joint to which the head-piece or helmet, the neck of which has a corresponding screw, can be attached or removed by one-eighth of a turn. Air is supplied by means of a flexible tube, which enters the helmet and communicates with an air-pump. To allow of the escape of the used air there is another flexible tube which is led from the back part of the helmet to the surface of the water. There is a signal line attached to the diving dress, by which the diver communicates with the attendants, and he car ries another line in his hand to guide him in returning to the rope or ladder by which he descends.
The helmet of the diving dress is usually made of tinned copper. There are several dif ferent types with special arrangement of valves for the air supply and exhaust. There are three windows in the head-piece, one-half inch thick glass secured in brass frames, the inlet valve in the helmet is non-return and is very import ant, as in the event of the air pipe being broken the valve closes and the diver is given a short time to realize his danger and act for safety. The breastplate and corselet are also carefully designed; they join the helmet to the body dress and preserve the air-tightness of the whole. It is necessary to add weight to the
diver to overcome the too great buoyancy which otherwise would cause him to rise to the surface or prevent his descent, due to his displacement. The cuffs at the wrists are made secure by vulcanized rubber rings. The air-connecting pipes from the pumps to the diver are so made and arranged that the least inconvenience due to weight will be experienced by them. The boots are of stout leather with wooden soles and lead over soles. Electric lamps and tele phones are provided, so that not only has the diver the best means of seeing around him but can communicate with those above him regarding his operations and be communicated with.
A diving apparatus now in use makes the diver independent of any connection with per sons above the water. A strong metallic air reservoir of steel is carried on the diver's back. A respiratory tube issues from the chamber and is terminated by a mouth-piece which is held between his lips and teeth. This tube is fur nished with a valve which permits the expulsion of air, but opposes the entrance of water. When the diver wishes to leave the water he inflates his dress with air from his reservoir and imme diately rises to the surface. The greatest depth, and the pressure consequent upon it, which has been found safe for a diver of experience and of good physique to descend to, is 35 fathoms, the pressure being about 100 pounds. The pres sure on the outside of the diver's dress due to the head of water is counterbalanced in the inside by the air pressure delivered by the air pump. Consult Bo(cott, 'Compressed Air Work and Diving) (London 1909) ; Dunville Fife, 'Submarine Engineering of To-day' (Lon don and Philadelphia 1914) ; British Admiralty 'Report of the Committee on Deep-Water Div ing' (London 1907) ; Siebe, Gorman & Company, Apparatus,) with notes and tables for the guidance of those conducting diving opera tions (London 1916).