a
windlass placed at the other end of the barge, the pole being prevented
from rising by a hitched rope which caused the "spoon" to penetrate the
bottom and fill the bag. When the "spoon" reached the end of the barge
where the windlass was placed, the winding was still continued, and the
suspended rope being nearly perpendicular the "bag" was raised to the
gunwale of the barge and the excavated material emptied into the barge.
The "bag" was then hauled back to the opposite end to be lowered for
another supply. This system is still in use, but is only adaptable to a
limited depth of water and a soft bottom; it has been largely used in
canals and frequently in the Thames. At the Fosdyke Canal in
Lincolnshire 135,000 tons were raised in the manner described. According
to J. J. Webster (_Proc. Inst. C. E._ vol. 89), the first application
of steam power for dredging operations was to a "spoon & bag" dredger
for cleansing Sunderland harbour, the engine being made by Messrs
Boulton & Watt of Soho, Birmingham.

_Dredging by Bucket between Two Lighters._--Another plan of dredging,
practised at an early period in rivers of considerable breadth, was to
moor two barges, one on each side of the river. Between them was slung
an iron dredging bucket, which was attached to both barges by chains
wound on the barrels of a crab winch worked by six men in one barge and
round a simple windlass worked by two men in the other barge. The
bucket, being lowered at the side of the barge carrying the windlass,
was drawn across the bottom of the river by the crab winch on the other
barge; and having been raised and emptied, it was hauled across by the
opposite windlass for repetition of the process. This process was in use
in the River Tay until 1833.

_Bucket Ladder Dredgers._--The earliest record of a bucket ladder
dredger is contained in the first paper of the first volume (1836) of
the _Transactions_ of the Institution of Civil Engineers. This machine
was brought into use at the Hull Docks about 1782. The bucket chain was
driven by two horses working a horse-gear on the deck of the vessel. The
buckets were constructed of 5/8 in. bars of iron spaced 1/8 in. apart,
and were 4 ft. long, 13 in. deep, 12 in. wide at the mouth and about 6
in. wide at the bottom. This dredger raised about 30 tons per hour at
the cost of 2-1/2d. per ton, which covered the wages of three men working
the dredger, eight men working the lighters and the keep of three
hor