g 500 tons or more of excavation and of steaming loaded at a
speed of about 9 m. per hour. These hopper barges are made with hinged
flaps in their bottoms, which can be opened when the place of deposit is
reached and the dredgings easily and quickly discharged.

Good examples of these vessels are the two steam hopper barges built for
the Conservators of the river Thames in 1898. The dimensions are: length
190 ft., breadth 30 ft., depth 13 ft. 3 in., hopper capacity 900 tons.
They are propelled by a set of triple expansion engines of 1200 i.h.p.,
with two return-tube boilers having a working pressure of 160 lb.
Special appliances are provided to work the hopper doors by steam power
from independent engines placed at the forward end of the hopper. A
steam windlass is fixed forward and a steam capstan aft. The vessels are
fitted with cabins for the officers and crew. On their trial trip, the
hoppers having their full load, a speed of 11 knots was obtained, the
coal consumption being 1.44 lb. per i.h.p.

_Methods of Dredging._--In river dredging two systems are pursued. One
plan consists in excavating a series of longitudinal furrows parallel to
the axis of the stream; the other in dredging cross furrows from side to
side of the river. It is found that inequalities are left between the
longitudinal furrows when that system is practised, which do not occur,
to the same extent, in side or cross dredging; and cross dredging leaves
a more uniform bottom. In either case the dredger is moored from the
head and stern by chains about 250 fathoms in length. These chains in
improved dredgers are wound round windlasses worked by the engine, so
that the vessel can be moved ahead or astern by simply throwing them
into or out of gear. In longitudinal dredging the vessel is worked
forward by the head chain, while the buckets are at the same time
performing the excavation, so that a longitudinal trench is made in the
bottom of the river. After proceeding a certain length, the dredger is
stopped and permitted to drop down and commence a new longitudinal
furrow, parallel to the first one. In cross dredging, on the other hand,
the vessel is supplied with four additional moorings, two on each side,
and these chains are, like the head and stern chains, wound round
barrels worked by steam power. In cross dredging we may suppose the
vessel to be moored at one side of the channel to be excavated. The
bucket frame is set in motion, but instead of t