_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 2½d. per ton, which covered the wages of three men working the dredger, eight men working the lighters and the keep of three horses. A dredger of this kind and power would only work in ballast, mud or other soft material, but the machine was gradually improved and increased in capacity and power by different manufacturers until it became a very efficient machine in skilful hands, excavating and raising material from depths of 5 ft. to 60 ft. of water at a cost not very different from, and in many cases less than, that at which the same work could be performed on land. With the powerful dredgers now constructed, almost all materials, except solid rock or very large boulders, can be dredged with ease. Loose gravel is perhaps the most favourable material to work in, but a powerful dredger will readily break up and raise indurated beds of gravel, clay and boulders, and has even found its way through the surface of soft rock, though it will not penetrate very far into it. In some cases steel diggers alternating with the buckets on the bucket frame have been successfully employed. The construction of large steam dredgers is now carried on by many engineering firms. The main feature of the machine is the bucket ladder which is hung at the top end by eye straps to the frame of the vessel, and at the lower end by a chain reived in purchase blocks and connected to the hoisting gear, so that the ladder may be raised and lowered to suit the varying depths of water in which the dredger works. The upper tumbler for working the bucket chain is generally square or pentagonal in form and made of steel with loose steel wearing pieces securely bolted to it. The tumbler is securely keyed to the steel shaft which is connected by gearing and shafting to the steam engine, a friction block being inserted at a convenient point to prevent breakage should any hidden obstacle causing unusual strain be met with in the path of the buckets. The lower tumbler is similar in construction to the upper tumbler, but is usually pentagonal or hexagonal in shape. The buckets are generally made with steel backs to which the plating of the buckets is riveted; the cutting edge of the buckets consists of a strong steel bar suitably shaped and riveted to the body. The intermediate links are made of hammered iron or steel with removable steel bushes to take the wear of the connecting pins, which are also of steel. The hoisting gear may be driven either from the main engine by frictional gearing or by an independent set of engines. Six anchors and chains worked by powerful steam crabs are provided for regulating the position of the dredger in regard to its work.