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volume of the “ Transactions” of the Institution, we haveextracted the following brief sketch.

The medium width of the river at the site of the bridgemay be taken at about 2,350 feet, the strength of the currentafter heavy land-floods is very great, and the site so muchexposed, that it is not uncommon for the ships lying in thevicinity of the bridge to drag their moorings. The bridgeis a large flat-bottomed vessel, of a width nearly equal toits length. The vessel is divided in the direction of itslength into three parts—the middle one being appropriatedto the machinery—each of the side divisions to carriages, &c.These side divisions or decks are raised about 2 feet abovethe line of flotation, and by means of movable platforms, aneasy communication is afforded with the shore on embarkingor landing. The bridge is guided by two chains, whichpassing through it over cast-iron wheels, are laid across theriver and fastened to the opposite shores, forming as it werea road along which the vessel travels backwards and forwards.

The moving power employed is two small steam-enginesturning a shaft, on each end of which is a large iron wheelwhereon the guide-chains rest. The peripheries of thesewheels are cast with sockets fitted to the links of the chains,so that when the bridge is put in motion by the steam-engines, it is moved in the reverse direction of, and with thesame velocity as the wheels. The ends of the chains havebalance-weiglqs attached to them, which rise or fall as thetension of the chains becomes more or less.

A similar bridge has been established at Portsmouth, andplies between that place and Gosport.

Under this article we may also mention Portable Bridges,which are easily taken to pieces, and as readily put togetheragain. M. Couplet speaks of a bridge of this kind, 200 feetlong, carried by 40 men.

Writers on architecture have bestowed considerable atten-tion on the subject of bridge-building, which is justly esteemedas one of the most noble and striking specimens of humanart. The earliest of these is Alberti, a native of Florence,who flourished about the middle of the loth century ; hehas given several judicious precepts, which, with littlealteration, were afterwards laid down by Palladio, Serlio ,and Seamozzi. The best of these rules are likewise givenby Goldman and Baukhurst, as well as by Hawkesmoor, inhis History of London Bridge. —M. Gautier has written alarge volume on bridges, ancient and modern.—M. Belidorhas trea.ted on this subject, in his Architecture Ilydravlique;us has M. Parent, in his Essais et RechercMs Mathematiques,vol. iii.—De la Hire , too, has touched on it, in his Traitede Meclianique. —Perronet has given the result of his expe-rience in a magnificent work, which,has acquired him greatcredit in France.—Bosset has given an excellent treatise onbridge-building, in the Memoires de 1 Academic. —Regemortespublished, in 1771, an account of the bridge built by himover the Allier, at Moulins. —In 1760, Mr. Riou publisheda work, entitled, Short Principles for the Architecture ofBridges; and Mr. Semple has given some excellent prac-tical remarks in his Treatise on Building in Hater, publishedin 1776. Other writers on the construction and principlesof arches and bridges, are Muller, Labelye, Atwood,Emerson, and Dr. Hutton.

‘When a bridge is constructed of stone, and arched over,it requires, in the act of building, to be supported upona mould, called a centre ; the construction of which is shownunder the article Centre.

Bridge Board. See Notch Board.

Bridge over : when there are any number of paralleltimbers, and another piece fixed transversely over them,then the transverse piece is said to bridge over the other

parallel pieces. In framed roofing, the common raftersbridge over the purlins ; likewise in framed flooring, theupper joists, to which the boarding is fixed, bridge overthe beams or binding joists, and are therefore called bridgingjoists.

Bridge Stone, a stone laid from the pavement to theentrance-door of a house, over a sunk area, not supported •by an arch.

BRIDGED GUTTERS, those made with boards, sup-ported below with bearers, and covered above with lead.

BRIDGING FLOORS, those in which bridging joistsare used. See Naked Flooring.

Bridging Joists, those which are sustained by transversebeams below, called binding-joists; also those on which theboarding for walking upon is nailed or fixed. See NakedFlooring.

BRIDGINGS, or Bridging Pieces. See StrainingPieces, and Strutting Pieces.

BRING UP, a term used by workmen for carrying upthe walls to it certain height: they say, “ bring up that partbut the term carry up is more frequently used.

BROACH, an old English term for a spire, still in usein the north of England. The term is specifically appliedto spires which spring directly from the eaves of the toweror other substructure, without the intervention of a parapet.This kind of spire is confined more especially to the earlierstyles of Gothic architecture ; in the later ones, the parapetis seldom dispensed with.

BROAD-STONE, the same as Free-Stone.

BRONZE; a compound of copper and other metals,especially zinc. It is used for cannon, medals, &c.

Bronze also denotes any piece of sculpture made of bronzemetal, as statues, busts, &c., whether in imitation of theantique, or representing a modern prototype. The methodof casting bronzes is described under Casting.

BROWN, a dusky colour inclining to redness. Of thisthere are various shades, distinguished by different appella-tions, as Spanish brown, sad broivn, tawny brown, London brown, and clove brown. Spanish brown is a dark dull red,of a horseflesh colour, of great use to painters, being generallyused in house-painting, for priming the timber work, or firstcoating. The best is that of a deep colour, and free fromstones. It is best and brightest when burnt in the fire tillit is red-hot. The various browns used in drawing areBistre, Cologne Earth, and Umber.

BRUNELLESCHI, Fiiilip, the son of a notary, born atFlorence in 1377, was at first designed for the bar ; butnot liking that profession, he was apprenticed to a goldsmith.His genius, however, turned him to the study of sculpture,geometry, and architecture. The first model by which heformed his taste in architecture was the church of St. John,at Florence, a building of good style, and much inclining tothe antique ; he afterwards went to Rome , to study theancient monuments there, the best of which he measuredand took drawings from ; and he is said to have first dis-tinguished the three ancient orders.

When the Florentines first thought of raising a dome uponthe church of St. Mary del Fiore, they invited all the primcipal architects of Europe to a consultation, at which Bn 1 'nelleschi proposed a double cupola, with a space between theinner and outer vaults, sufficient to admit of staircases andpassages to the top. This idea was deemed so preposterous,that he was actually turned out of the assembly, for havin 0presumed to insult the good sense and judgment of so manyexperienced artists, who had never heard of such a thing,and held it to be impracticable. Undaunted by this treat'ment, Brunelleschi persisted in maintaining the practicability