action. The block is lowered by its own crane on to the bottom. The
bell descends upon it, and the crew seize it with tackle suspended
inside the bell. Instructions are sent up as to the direction in which
the bell should be moved with its burden, and as soon as the exact spot
has been reached the signal for lowering is given, and the stone settles
on to the cement laid ready for it."[34]

For many purposes it is necessary that the worker should have more
freedom of action than is possible when he is cooped up inside an iron
box. Hence the invention of the

DIVING-DRESS,

which consists of two main parts, the helmet and the dress proper. The
helmet (Fig. 161) is made of copper. A breastplate, B, shaped to fit the
shoulders, has at the neck a segmental screw bayonet-joint. The
headpiece is fitted with a corresponding screw, which can be attached or
removed by one-eighth of a turn. The neck edge of the dress, which is
made in one piece, legs, arms, body and all, is attached to the
breastplate by means of the plate P^1, screwed down tightly on it by
the wing-nuts N N, the bolts of which pass through the breastplate. Air
enters the helmet through a valve situated at the back, and is led
through tubes along the inside to the front. This valve closes
automatically if any accident cuts off the air supply, and encloses
sufficient air in the dress to allow the diver to regain the surface.
The outlet valve O V can be adjusted by the diver to maintain any
pressure. At the sides of the headpiece are two hooks, H, over which
pass the cords connecting the heavy lead weights of 40 lbs. each hanging
on the diver's breast and back. These weights are also attached to the
knobs K K. A pair of boots, having 17 lbs. of lead each in the soles,
complete the dress. Three glazed windows are placed in the headpiece,
that in the front, R W, being removable, so that the diver may gain free
access to the air when he is above water without being obliged to take
off the helmet.

[Illustration: FIG. 161.--A diver's helmet.]

By means of telephone wires built into the life-line (which passes
under the diver's arms and is used for lowering and hoisting) easy
communication is established between the diver and his attendants above.
The transmitter of the telephone is placed inside the helmet between the
front and a side window, the receiver and the button of an electric bell
in the crown. This last he can press by raising his head. The life-line
s