1054

THEORY AND PRACTICE OF ENGINEERING.

Book II.

another bell has been since cast, 6 feet long and 4 feet broad, which permits the workmento proceed with greater alacrity.

The Camel is a machine used in Holland for raising ships by the buoyant power of water;it is a very ingenious contrivance, and consists of two similar hollow vessels, so constructedthat they can be applied on each side of the hull of a ship ; these hollow vessels aremade water-tight, and on the deck of each windlasses are attached, by wdiich ropes, whichare made to pass under the keel of the vessel to be raised, are worked. When the camel isemployed to raise a ship, the water is allowed to fill each half of it, and when the ropesfirmly unite the ship to the camel, the water is pumped out, and the buoyancy of the hollow

vessels raises the ship up.

The length of one of these camels employed to float vessels over the sands in Hollandwas 127 feet, the breadth at one end 22 feet, and the other 13 feet: the hollow partw’as divided into several compartments.

A vessel drawing 15 feet water could by this means he made to draw only 11 feet, andthe largest man-of-war in the Dutch service could be made to pass the sand banks of theZuyder Zee. Meuves Meindertszoon Bakker invented this curious machine at Amsterdam about 1688 : it has been used at Venice , on the Tiber, and elsewhere with success.

The camel is an excellent example to show that when a body is held beneath the surfaceof a fluid, the force with which it will ascend, if it he lighter than the fluid, or with whichit will descend if it be heavier, is equal to tbe difference between its own weight and theweight of an equal quantity of fluid. Ice by the same means can remove enormous massesof rock, it being specifically lighter than water: when a river is frozen, and large stonessurrounded by ice, the upward pressure of lift exerted upon them so far exceeds thatexerted downwards, that they are brought to the surface, and then floated by the ice, andoften carried to a great distance.

The Pontoon , made either of timber or copper, acts somewhat upon the same principle :when applied to close the mouth of a canal or entrance to a dock, they are sunk or raisedby either letting in orpumping out the wa-ter they contain, andit is by an adjustmentof its contents that itcan be kept at anyheight, shown by thelines figured l, 2, 3, 4,

5, 6, 7, 8, 9. If it berequired that watershould pass to or fromthe canal or dock,the pumps which arewithin the pontoon areworked sufficiently tolighten it and allowit to rise, or if it benecessary to lower it,this can be effectedby admitting thewater within it, bymean 1 : of a pipe andturncock, shown inthe transverse section.

The letters A,B, C,

D, E, show the width

of the corresponding parts of the plan and end elevation, as do the figures marked uponit and the transverse section. Such a contrivance working in two grooves effects thesame purpose as lock-gates, but when it is required to allow the passage of any vessel, it isnecessary that the pontoon should be floated out of its position and be moored aside: suchpontoons or lighters are found serviceable at ferries and piers, where the height of the watervaries with the tides.

Raising Vessels when sunk at Sea : one of the most celebrated efforts of this kind wasrecorded by the senator Zusto, by order of the Venetian government, after the ship of theline of 74 guns, named the Phoenix, which had sunk in the year 1783 in the canal ofSpignon, near the entrance of the Lagune, was raised by the Chevalier Morelatto, a distin-guished naval officer in the employ of the republic.

The Phoenix, sunk in a depth of 36 feet of water, and bedded several feet in the mud,was considerably injured by the concussions it had experienced in its descent; it wastherefore necessary, not only that the weight of the vessel should be sustained, but that

j V/ATCH

Fig. 1620.

PONTOONS.