Chap. XIII.

DREDGING.

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series of iron or copper scuttles attached to a chain, which like a chapelet works round abeam elevated at the side of the vessel, and brings up large quantities of ballast at each dip.

The fly-wheel of the dredging machine is turned by a large spur-wheel, fixed on theshaft, acting in a pinion on the axis of the fly-wheel, to give it a greater velocity than thecrank, by which means a smaller fly-wheel is sufficient to regulate the motion of the engine.

The motion is conveyed from the steam-engine to the chain barrels by the inclined shaft,shown in the section ; at the lower end is a bevelled wheel, which receives its motion fromanother fixed on the main shaft of the engine. At the upper end also of the inclined shaftis another bevelled wheel, working in another fixed to the shaft, and situated in a linewith the centre ot the two chain barrels : at the two extremities of this shaft are twowheels, which communicate power to the chain barrels, and bring up the ballast ; anengine of 16 horse-power, dredging on a moderate depth, will raise 35 tons in an hour,and consume about 343 pounds ot Newcastle coal in that time.

DREDGING MACHINE.

The upper rollers is a square barrel, as is that at the lower end, and around them passesthe double endless chain, each alternate link of which carries a bucket; these are piercedfull of holes, to allow the water to drain out as the sand or gravel is brought up. Themouths have a semicircular form, to prevent their sticking fast during the operation.

DREDGING MACHINE.

Dredging machines of this kind are usually mounted in the hulk of an old sloop of 100tons burthen, and no expense should be spared in making it strong and substantial; forafter the machinery is introduced, the smallest twisting of the vessel occasions fracture ofthe wheels, or some other portion. The bucket frame is found to work best when at anangle of 45 degrees.

Artesian Wells have been considered of great importance, since their introduction nearLondon in 1794, when one was sunk at Norland House, on the N. W. of the residence ofLord Holland at Kensington, and which is described in the Philosophical Transactions of 1797.

The water was derived from sandy strata, of the plastic clay formation, but so much sandwas brought up, that the pipes were constantly obstructed : it was therefore found necessaryto pass through the loose strata, and obtain the water from the chalk.

31. Hericart de Thury , 31. Arago, and 31. Von Bruckinann, have all drawn attention tothis subject, and shown that throughout Europe there are extensive districts where, undercertain conditions of geological structure, and at certain levels, water maybe raised to the

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