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

As a diver enters the water, the superfluous air in his dress is driven out through the outlet valve by the pressure of the water on his legs and body. The water seems to grip him all round. If the valve is freely open, he will feel his breathing rather laboured by the time he gets his valve just under water. The reason of this is that the pressure in his lungs is that of the water at the valve outlet, whereas the pressure on his chest and abdomen is greater by something like a foot of water. He is thus breathing against pressure, and if he has to breathe deeply, as during exertion, the effect becomes serious. One of the first things, therefore, that a diver has to learn is to avoid this adverse pressure by adjusting the pressure of the spring on the outlet valve, so that the breathing is always quite free. The spring on the valve at the same time regulates the amount of air in the dress, and therefore the buoyancy of the diver. A practised diver can thus slip easily, and without exertion, up or down the shot>rope. The breathing is, of course, easiest when the dress is full of air down to the level of the abdomen ; but, when this is so, tha diver runs a risk of being “ blown up.” It will also be readily understood that a horizontal, or nearly horizontal, position is the easiest one for a diver s breathing, and many divers work crawling on the ground. In this position it may happen that too much air gets into the dress. If this air is allowed to get into the legs of the dress, the diver is capsized and blown helplessly to the surface, or he may be caught by a rope or other obstruction, and hung up in a helpless position with his legs upwards, the excess of air being unable to escape at the outlet valve since it is downwards. To avoid this risk, the arrangement for lacing up the legs, as shown in photo No. 5, page 13, is recommended. With the legs laced up, the head always comes uppermost if the diver tends to float upwards, hence the excess of air escapes by the valve. 6 b