the water on the legs and body, and by the time the top of the
diver's head reaches the surface his breathing becomes
laboured, because the pressure of air in his lungs equals the
atmospheric pressure, while the pressure upon his chest and
abdomen is greater by the weight of the water thereon.

He is thus breathing against a pressure, and if he has to
breathe deeply, as during exertion, the effect becomes serious;
so that the first thing he has to learn is to adjust the
pressure of the spring on the outlet valve, so that the amount
of air pumped in under pressure and retained in the diving
dress counterbalances the pressure of the water outside, which
is equal to a little under 1/2lb per square inch for every foot
in depth. If the diver be 6 ft tall, and stands in an upright
position, the pressure on his helmet will be about 3lb per
square inch less than on his boots. The breathing is easier if
the dress is kept inflated down to the abdomen, but in this
case there is danger of the diver being capsized and floating
feet upwards, in which position he is helpless, and the air
cannot escape by the outlet valve. Air is supplied to the diver
under pressure by an air pump through a flexible tube called
the air pipe; and a light rope called a life line, which is
used for signalling, connects the man with the surface. The
descent is made by a 3 in "shot-rope," which has a heavy sinker
weighing about 50 lb attached, and is previously lowered to the
bottom. A 1-1/4 in rope about 15 ft long, called a "distance-
line," is attached to the shot-rope about 3 ft above the
sinker, and on reaching the bottom the diver takes this line
with him to enable him to find his way back to the shot-rope,
and thus reach the surface comfortably, instead of being hauled