Diving

Diving, the art of immersing one's self in, and remaining under, water for limited periods. It is pursued with or without the aid of artificial ap pliances. The chief difficulties to be contended with are lack of air and pressure of water, the latter, even at slight depths, being considerable, and at great ones terrible. A practised naked diver has been known to subsist under water for a little over two minutes, but the time is, of course, insufficient for the performance of much work; and, to enable divers to prolong it, many devices have been made use of. The earliest of these is the Diving Bell, a strong vessel usually made in the form of a truncated cone, with the smaller and upper end closed and the lower one open. It is so suspended that, when lowered into the water with the diver inside it, it may sink full of air, and with its base parallel with the horizon. The air hinders the rise of water within, though the deeper the apparatus, the greater the pressure, and consequently the higher the rise. At thirty-three feet, "jjwhen the pressure of the water equals that of the atmosphere, the bell becomes half full. To keep the water within limits, air under pressure is generally pumped into the bell. The diving bell was perfected by Spalding and others, but as its arrangements prevented the diver from going far away from it, it has, save for particular purposes, been generally superseded by one or other of the numerous forms of diving suits and helmets. The first diving suit seems to have been invented by Borelli. The principle, in its simplicity, is the placing of the diver's head in a water-tight chamber or helmet into which supplies of fresh air are continually pumped from above, the foul air being at the same time allowed to escape by means of a tube or a valve. The helmet is fitted with glass eyeholes. The bare principle has been developed in many directions. To some helmets are now attached reservoirs of compressed fresh air, which are placed under the control of the diver. Such is the apparatus of Rouquairol. Fleuss's helmet is connected with a portable supply of compressed oxygen, and arrangements are made whereby the air that has been breathed by the diver is purified by being passed through a solution of caustic soda. The wearer of such a helmet is, for a time, independent of communication with a boat or with the shore.