boilers. Two independent series of pumps, with separate connections,
feed the hydraulic lifting apparatus, thus permitting repairs to be
made when necessary, without interrupting the work. A special machine
with three cylinders drives the pumps of the condenser. An accumulator
regulates the hydraulic pressure and serves to raise or lower the
spuds.

At the end of the Suez Canal next to the Red Sea, the bottom consists
of various conglomerates containing gypsum, sandstone and sometimes
shells. It was upon a bed of this nature that the machine was first
put to work. The mean depth of water, originally 8.25 meters (26 ft. 3
in.), was for a long time sufficient for the traffic of the canal; but
as the variations in level of the Red Sea are from 1.8 to 3 meters (5
ft. 11 in. to 9 ft. 10 in.), the depth at the moment of low water is
scarcely adequate for the constantly increasing draught of water of
the steamers. Attempts were made to attack the rocky surface of the
bottom with powerful dredges, but this method was expensive because it
necessitated constant repairs to the dredges.

[Illustration: FIG. 3.--DREDGE MOVEMENT.]

These last, although of good construction, seldom raised more than 153
cubic meters (200 cubic yards) in from eight to fifteen days. Their
daily advance was often only from sixty to ninety centimeters (about 2
to 3 ft.), while with the "Derocheuse" it was possible to advance ten
times as rapidly in dredging to the same depth. The bottom upon which
the machine commenced its work was clean and of a true rocky nature.
It was soon perceived that this conglomerate, rich in gypsum,
possessed too great elasticity for the pointed battering rams to have
their proper effect upon it. Each blow made a hole of from fifteen to