A Treatise On The Principles And Practice Of Harbour Engineering

SÜRVEYING, MARINE AND SUBMARINE. 55 water and surmounted by a spécial chamber, known as an air-lock. This chamber has two tightly fitting doors ; one giving on to the open, and the other in to the tube. After entrance to the chamber from above or below, the door is closed and the pressure equalised with that of the bell or the atmosphère as the case may be. The air-lock thus forms a convenient means for the transmission of material to and from the base of operations—for the passing out of excavation and the taking in of stone and cement; and it becomes, in fact, essential, if the progress of the work is to be uninterrupted. In many cases, however, owing to the bulk and weight of the foregoing apparatus, submarine operations have been mainly, and even entirely, carried on with the aid of individual divers, each equipped with a helmet diving-dress and capable of acting in perfect independence of any submerged chamber. Where the locality is free from currents, there can be little doubt that this method of working is preferable in many ways ; but a current exceeding 3 miles per hour constitutes not only a trying force for the diver to contend against, but it throws considerable strain on the air-pipe and, to a less degree perhaps, upon the life-line. It must be borne in mind that a diver, when immersed, is a very buoyant object, and that he necessarily finds it difficult to withstand any powerful lateral force. It is comparatively easy for him to be swept off his feet, and even a moderate flow makes his foothold far from secure. The author recollects with painful vividness how one diver, engaged on submarine work at Liverpool, was suddenly sucked through a culvert to his death. There was gross negligence which contributed to the fatal result, but the incident illustrâtes the uncertainty of a diver’s equilibrium and the great risk he oftentimes runs. Apart from this drawback, it must be admitted that work, as a rule, can be more expeditiously performed by men moving in perfect freedom over a large area than is possible when they are confined within a narrow space, where there is a limit to the number of men employable and the likelihood of their impeding one another’s movements. Diving’Dresses. —The diver’s outfit comprises the helmet, the dress, the air-pipe and life-line, and the air-pump. The helmet, which is spherical in appearance, is of highly planished tinned copper, as also is the breastplate or corselet to which it is connected, though gun-metal is sometimes employed for the latter. Connection is effected by means of segmental screw neck-rings of gun-metal, the joint being rendered perfectly water-tight by turning the helmet through an angle of 45 degrees. The breastplate is moulded to the shape of the shoulders on which it sits, sometimes with a padded bearing. It receives the collar of the india-rubber dress over a series of brass screws through corresponding eyelet holes. Gun- metal flanges and wing nuts form a secure and impervious connection. The headpiece is fitted with side and front lights in the form of round or oval plate glasses, set in brass frames, with stout wire-guards. The front glass is detachable by unscrewing, or hinged to open. Air should be introduced into the helmet in such a way as to pass closely over the surfaces of these glasses,