, or Pontoon, a kind of flat-bottomed boat, whose carcass of wood is lined within and without with tin. Some nations line them on the outside only, and that with plates of copper, which is better. Our Pontoons are 21 feet long, nearly 5 feet broad, and 2 feet 1 1/2 inch deep within. They are carried along with an army upon carriages, to make temporary bridges, called Pontoon-bridges. See the next article.

Pontoon-Bridge, a bridge made of Pontoons slipped into the water, and moored by anchors and o<*>herwife fastened together by ropes, at small distances from one another; then covered by beams of timber passing over them; upon which is laid a flooring of boards. By this means, whole armies of infantry, cavalry, and artillery are quickly passed over rivers.—For want of Pontoons, &c, bridges are sometimes formed of empty powder casks, or powder barrels, which support the beams and flooring. Julius Cæsar and Aulus Gellius both mention Pontoons (pontones); but theirs were no more than a kind of square flat vessels, proper for carrying over horse &c.

PONT-Volant, or Flying-bridge, is a kind of bridge used in sieges, for surprising a post or outwork that has but narrow moats. It is made of two small bridges laid over each other, and so contrived that, by means of cords and pullies placed along the sides of the under bridge, the upper may be pushed forwards, till it join the place where it is designed to be sixed. The whole length of both ought not to be above 5 fathoms, lest it should break with the weight of the men.

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Entry taken from A Mathematical and Philosophical Dictionary, by Charles Hutton, 1796.

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PORTA (John Baptista)