Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

“ Blowing up.” Pressure on the ears. Work on the Pump. Effect of compressed air on the voice. The danger in falling is due to the sudden diminution in the volume of the air; sudden ascents may be just as dangerous. A special danger of a sudden ascent is associated with the absorption of the air by the blood, and will be con- sidered later. A diver in preparing to ascend tightens up the valve to increase his buoyancy and allows himself more or less to float up the shot rope. II the valve is closed more than will allow the excess of air to escape, his ascent will, at first, be gradual, but soon, with each foot of ascent, the volume of air in the dress expands and his speed is quickened. At first the limbs are more or less capable of movement, and the diver has a chance of holding- on to the rope and adjusting- his valve, but verv soon the dress becomes so very much expanded that it is as hard as a board, and he cannot reach the valve : he is oracticallv powerless. If the dress were to «rive wav anywhere near the head under the strain, which fortvn^tolv i<< verv unlikelv. since the air alwavs cscaoes through the cuffs, the diver mie+t he in a still worse predicament, for if the attendant failed to haul in the slack of the life-line quickly enough he mi^ht sink like a stone, and be crushed by the pressure due to the depth he had fallen. One other effect we have to notice is the pressure on the ears. The ear may be compared with a cavalry drum, which has a parchment covering at one end only. If we were to place such a drum in a caisson or other air chamber, and pump in air, we should verv soon find that the head of the drum was beingr forced in ; but if we made a hole in the body of the drum there would be no change, since the pressure on the inside would always be equal to that on the outside. The condi- tion of the ear is the same as that of the drum. The middle car is the bodv of the drum, and across one end is stretched the “ drum of the ear; at the other end is a tube which leads into the nose and allows the air pressure on the inside of the ear to become equal to the pressure outside. But often, from a slight cold or other cause, the tube leading to the nose becomes blocked up, and we have pains in the ear until the passage is cleared. In the case of a diver this is best done by stopping in his descent for a moment and swallowing' his saliva, as the action of swallowing oocns the tube. If he cannot open the tube he must come up again. Usually, if the diver can reach five or six fathoms he will have little difficulty in attaining greater depths, where the relative differences in volume of the air become less and less. The effect of the law of pressure on the work of the pump can be considered here. As the diver requires the same volume of air at whatever depth he may be, if the pumps are taking in one cubic foot a minute when the diver is near the sur face, they must take in two cubic feet when the diver is at 33 feet, three cubic feet at 66, four cubic feet at 99, and so on. But not only have the pumps to take in and deliver a much larger quantity of air ; they have also to deliver it against a rapidly increasing pressure, so that the work is greatly increased. We saw that the density of the air increased with the pressure ; this leads to certain effects in connection with the voice, which at very great depths has a “ Punch ”-like quality, which is very distinctly noticed through the telephone. A diver cannot whistle when in deep water, as the density of the air hinders the vibration of the lips. 15 12