1058

THEORY AND PRACTICE OF ENGINEERING.

Rook 11.

in a lantern turned the cylinders, and they in their motion brought up the loaded scuttlesmade fast to the endless chain : when either of the scuttles had arrived above the uppercylinders* it became inclined, and deposited its contents, which were immediately drawnaway by a vessel or trough, and in this manner the scuttles were kept in motion and dis-charged.

When the depth was greater or less, the machine was made to accommodate itself by theintroduction or taking away of some of the links, and mounting higher the two lowercylinders.

The winches being turned, moved the lantern fixed to their common axis ; this engaging ina toothed wheel fixed to the upper cylinder, in turning drew the chain and scuttle attachedto it, and also turning round, occasioned the descending scuttle to enter the ground, and toelevate the loaded one to the top of the machine, where it was thrown over, and depositedits contents upon a hinged trough, attended by a workman, who directed its further course.

Peyronnet describes a similar machine, and also furnishes the dimensions for its con-struction, and the cost in his time : he makes the chain 17 inches in length, and placesupon it six scuttles. The cylinders were formed of elm, hooped with iron, and coveredwith strips of plate iron : this machine, mounted on two boats, was employed with two othersat the bridge of Orleans, and each was worked by six men, who raised about twelve cubeyards per day, from a depth of upwards of 6 feet: such a machine was preferred to clearout the cofferdams to the scoop previously used, which had, by means of a handle, the poweronly of clearing the entire width between two rows of piles; it was drawn up anddown by a rope attached to it, worked by a capstan. The scuttles answered admi-rably well, where the bottom was not stony, but great care is requisite in the manufactureof the chains; the best were those made with bolts and screws, as they facilitated thelengthening and shortening.

We find in many of the works published in the sixteenth century descriptions of dredgingmachines, and at the commencement of the following century, Savory patented an inventionfor raising ballast out of rivers by steam : and Cornelius Meyer, a Dutch engineer, aboutthe vear 1680, contrived a machine, which strongly resembled the one in use, with thisexception, that boards were made to lift the ballast, and a horse wheel was employed.Mortier and Hertel, Dutch engineers, also turned their attention to this subject, and Balmemade a vertical wheel, which worked between two boats armed with six buckets, whichlifted avast deal of mud ; these and many other inventions were brought over to Eng-land, and used in the time of Charles I. for dredging the fens, both in Lincolnshire andYorkshire ; and from them great improvements were afterwards made: from the evidenceof Mr. Watts, we find that in 1796 he manufactured an engine for dredging to be em-ployed in the harbour at Sunderland.

The Bag and Sj>oon, which has succeeded the box-shovel, consists of a ring of malleableiron, 2 feet in diameter, and 2 feet 4 inches deep, sharpened and steeled on the under side,4 inches broad, for about one third of its circumference, and pierced on the inner edge withholes for the lacing of the bag. The remainder of the ring is of round iron, 1^ inch indiameter, and on the upper side, or that opposite to the mouth, a hose is welded to receivethe pole or handle, the length of which must be in proportion to the depth to be dredged :on eaeli side, about half way up the spoon, is fastened a chain 30 inches in length, whichis united by a ring at top, where the working rope is made fast: the bag is made ofstrong tanned leather, about 3.^ feet in depth, laced with leather thongs to the spoon, and asufficient number of holes is pierced through the bag to allow the water to escape. Aflat-built barge, of thirtv or forty tons burthen, is usually employed to work this machine,and all that is required is a small projecting crane, so made that it can be readily thrownout of gear.

The Bucket dredging Machine, worked by steam, is now universally adopted to deepenall navigable rivers, harbours, and docks, or wherever any accumulation of mud or sandis required to be removed. The contrivances of Perronet, and other French engineers,applied to the machine earlv used at Venice, no doubt gave rise to the introduction of thisvery powerful one, now almost indispensable in all ports.

Mr. John Iluges seems to have been the first who used it in clearing out the bed of theThames, about the year 1804; that originally contrived was apparently very defective,but after expending a considerable sum of money, he brought the machine to such perfection,that in one day he was enabled to raise, opposite to Woolwich, 2000 tons, where therewas a depth of water of more than 30 feet. On this occasion it was constructed in an oldbomb-vessel, and bad a thirty-horse engine, the whole costing nearly 8000 pounds. In allprobability it was similar in plan to the first, made by Boulton and Watt, which was fixedin a boat, and had four rollers, each of which had one spoon ; the rollers were made tomove at the rate of 10 feet per minute, and each spoon could bring up 15 cwt. at a time.

The machine employed bv the Hull Dock Company in 1802 had eleven wooden scuttlesworking on a ladder that passed over rollers, the motion given by a horse-wheel: those nowused in the harbours and navigable rivers, worked by powerful steam-engines, have a