-contained Diving Dress._--The object of the self-contained diving
dress is to make the diver independent of air supply from the surface.
The dress, helmet, boots and weights are of the ordinary pattern
already described, but instead of obtaining his air supply by means of
pumps and pipes, the diver is equipped with a knapsack consisting of a
steel cylinder containing oxygen compressed to a pressure of 120
atmospheres (= about 1800 lb.) to the square inch, and chambers
containing caustic soda or caustic potash. The helmet is connected to
the chambers by tubes, and the oxygen cylinder is similarly connected
to the chambers. The breath exhaled by the diver passes through a
valve into the caustic soda, which absorbs the carbonic acid, and it
is then again inhaled through another valve. This process of
regeneration goes on automatically, the requisite amount of oxygen
being restored to the breathed air in its passage through the
chambers. This type of apparatus has been used for shallow water work,
but the great majority of divers prefer the apparatus using pumps as
the source of the air supply.

An emergency dress, using this self-contained system for breathing,
has been designed by Messrs Fleuss and Davis, of the firm of Siebe,
Gorman & Co., primarily as a life-saving apparatus, for enabling men
to escape from disabled submarine boats.

The helmet diver is indispensable in connexion with harbour and dock
construction, bridge-building, pearl and sponge fishing, wreck raising
and the recovery of sunken cargo and treasure. Every ship in the
British navy carries one set or more of diving apparatus, for use in
ease of emergency, for clearing fouled propellers, cleaning valves or
ship's hull below the water line, repairing hulls if necessary, and
recovering lost anchors, chains, torpedoes, &c.

[Illustration: FIG. 5.--Submarine Electric Lamp, with and without
Reflector.

A, Metal case containing electrical fittings.
B, Glass globe and incandescent lamp.
C, Stand, which also protects the globe.
D, Ring for suspending lamp.
E, Reflector.]

_Greatest Depths attained._--The greatest depth at which useful work has
been performed by a diver is 182 ft. From this depth a Spanish diver,
Angel Erostarbe, recovered L9000 in silver bars from the wreck of the
steamer "Skyro," sunk off Cape Finisterre; Alexander Lambert succeeded
in salving L70,000 from the