DIVING (from dire, AS. dyfan, causative of dtifan. to plunge). The act of working under water—either with or without mechanical aids to enable respiration—as in pearl and sponge fishing, the raising of sunken vessels, the laying of subaqueous foundations, or other operations under water. Formerly diving operations were confined mostly to pearl and sponge fisheries and were performed by divers who plunged beneath the water, remained as long as they were able to do without respiration, and then returned to the surface with their load. It has been asserted that the pearl-divers of the East acquired by practice the power to remain under water for fifteen or twenty minutes. There is absolutely no truth in such assertion:, as no such endurance is possible; two, and sometimes three. minutes under water is the limit of endurance of the most skillful divers unaided by mechanical means to support respiration. Most divers suffer se verely from the continua] efforts in holding the breath: bloodshot eyes and the spitting of blood are common among them. This rude method of diving is hut little used now, oven in the pearl and sponge fisheries, where it is particularly ap plicable. Diving operations are now performed by means of diving-bells or special diving-dress.
Divixc;-11Ett. The raeab us aqua t inns, or aquatic kettle. described by 'falsifier as having been used by two Greeks in Spain, at Toledo, in 153S, in the presence of the Emperor V. and a multitude of spectators. is one of the earliest reliable aceounts of a diving-bell. From his description. this must have been similar in principle and construction to the modern div ing-hell. but of elumsy dimensions. and wanting in efficient means of renewing the supply of air. Dr. Valley's diving-bell. devised about 1720, was a wooden chamber, open at the bottom. where it was loaded with lead to keep it perpen dicular in its descent. Strong pieces of glass were set in the upper part to admit light. Casks filled with air, and loaded with lead. were let down with the bung-hole downward: and from these a supply of air was drawn by means of a hose. The form of tl iv ing-bel now in use was first constructed by for e work- at 1:a111-1,,ate Harbor, England, 17SS. It was ot and weighed 50 rut.; its feet : hngth. the same: and width, ft et. It sank by its own weight, and was .1,flited by stout pieces of bull's•eye glass firmly etmented by brass ring. near the top. The prin. tilde of the diking-bell will be easily understood by floating a piece of lighted candle or a wax match on a cork, and then covering it with an inverted tumbler, and pressing downward: the ,andle At ill descend below the level of the sur rounding Water. and continue burning for a short
time, although the tumbler he entirely immersed. The reason is obvious enough: the air in the tumbler, having no vent. remains in it. and pre vents the water front occupying its place. so that the cork and candle. though apparently under water. are still floating, and surrounded by the air in the tumbler; the candle continues burning until the oxygen of the air is exhausted. and then it goes out. as would the life of a man unfit r •imilar circumstances. If vessels full of air, like the barrels of Dr. Halley. were sub merged, aml their emitents poured into the tumbler, the light might be maintained; but this could better be done if a tube passed through the tumbler, and air were pumped front above through the tube into the tumbler.
An account of early diving-bells and apparatus will be found in Gerland and Traunitiller's .ch ich le der !'Iryxiko1i.schen Experi men( jer k rots, ( Leipzig, IS931.
The modern diving-bell. which is made of cast iron like Smeaton's, is supplied with air in this manner. It must remembered that air is compressible. and diminishes in bulk in propor tion to the pressure. co that at a depth of about :33 feet in water it would half the it filled at the surface: if the inverted tumbler were carried to this depth. it would lie half tilled with water. A considerable quantity of air has, therefore, to be pumped into the diving bell. merely to keep it full as it descends: the air thus compressed exerts a eorre-ponding pres sure. and would rush up with great force if the tube were open and free. Thi, is prevented by a valve opening downward When the diving-bell has reached it- full depth. the pump ing is continued to supply air for respiration: and the redundant air overflows. or rather ti mkt- flow., by the opcn mouth, and ,cend: to the surface in Imbbles. The diving-bell is provided with a platform or seat for the workmen, and suspended from a suitable crane or beams pro jecting from a barge or pier: men above are sta tioned to work the pumps and attend to the sighals of the bellanin. These signals are -imply made by striking the sides of the iron diving bell with a ban user, and as sound is freely communicated throng]) %valor, they are easily heard ow ino to their great weight and (bnasy operation, diving-bells are now seldom used in -nbaquettus operation:. the modern ap pliance being tin diving-dress or diving-armor.