ll plant in the form with which we are
familiar to-day, that celebrated engineer having designed a square bell
of iron, for use on the Ramsgate harbour works, in 1788. This bell,
which measured 4-1/2 ft. in length, 3 ft. in width and 4-1/2 ft. in height,
and weighed 2-1/2 tons, was made sufficiently heavy to sink by its own
weight. It afforded room enough for two men to work, and was supplied
with air by a force pump worked from a boat at the surface.

Though the diving bell has been largely superseded by the modern diving
apparatus, it is still used on certain classes of work the magnitude of
which justifies the expense entailed, for it is not only a question of
the cost of the bell, but of the powerful steam-driven crane which is
needed to lower and raise it, and also of the gantry on which the crane
travels. Sometimes a barge or other vessel is used for working the bell.

At the present day, two types of diving bell are employed--the ordinary
bell, and the air-lock bell, which, however, is not so largely used.

On the new national harbour works at Dover, four large diving bells of
the ordinary type (fig. 6) were employed. These bells, in each of
which from four to six men descended at a time, consisted of steel
chambers, open at the bottom, measuring 17 ft. long by 10-1/2 ft. wide by
7 ft. high, and each weighed 35 tons. The ballast, which at once gives
the necessary sinking weight to the bell and maintains its
equilibrium, consisted of slabs of cast iron bolted to the walls of
the bell, inside. Each bell was fitted with loud-sounding telephonic
apparatus, by means of which the occupants could communicate either
with the men attending the crane or the men looking after the air
compressors at the surface. Electric lamps, supplied with current by a
dynamo in the compressor room, gave the necessary light inside the
bell. Seats and foot rails were provided for the men, and there were
racks and hooks for the various tools. Suspended from the roof was an
iron skip into which the men threw the excavated material, which was
emptied out when the bell was brought to the surface. Air was supplied
to the bells by means of steam-driven compressors worked in a house
erected on the gantry. The air was delivered into a steel air
receiver, and thence it passed through a flexible tube connected to a
gun-metal inlet valve in the roof of the diving bell; the pressure of
air was regulated accord