Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/809

 B R I ( t 7 ) B R I the fmalleft boats in their paflage through ene or more arches, built over a river, canal, or endanger the like, for the conveniency of croffing the fame. theItarches. confifts of thirteen large and two fmall arches, Bridges are a fort of edifices very difficult to exewith fourteen intermediate piers. cute, on account of the inconvenience of laying foun- together Each pier terminates with a faliant right angle adations, and walling under water. The parts of a gainft the two middle piers are each febridge are the piers, the arches ; the pavement, or venteeneitherfeetftream: in thicknefs at the fntinging of the way ever for cattle and carriages; the foot-way on arches, and contain thoufand cubic feet, or near each Tides for foot paffengej-s; the rail or parapet, two hundred tons ofthree ftone; and the others de~ which inclofes the whole; and the hutments or ends creafe in width equallyfolid on each fide by one foot. of the bridge on the bank. the arches of this bridge are femicircular; they The conditions required in a bridge are, that it be all All from about two feet above low-water mark; well-defigned, commodious, durable, and fuitably de- the fpring middle arch is feventy-fix feet wide, and the ocorated. The piers of ftone-bridges ffiould be equal thers in number, that there may be one arch in the middle, feet. decreafe in breadth equally on each fide by four where commonly the current is ftrongeft; their thickbridge is built of the beft materials ; and the nefs is not to be lefs than a fixth part of the fpan of fizeThis and difpofition of thefe materials are fuch, that the arch, nor more than a fourth; they are common- there is no falfe bearing, or fo much as a falfe joint in ly guarded in the front with angular fterlings, to break the force of the current: the ftrongeft arches are thofe the whole ftruflure ; befides that, it is built in a neat whofe fweep is a whole femicircle;. as the piers of brid- and elegant tafte, and with fuch fimplicity and granges always diminiffi the bed of a river, in cafe of inunda- deur, that, whether viewed from the water, or by tions, the bed niuft be funk or hollowed in proportion the paffengers who walk over it, it fills the mind with to the fpace taken up by the piers (as the waters gain an agreeable furprize. The femioftangular towers, in depth what they lofe in breadth) which otherwife which form the recefles of the foot-way, the manner conduce to waffi away the foundation and endanger the of placing the lamps, and the height of the baluftrade, piers: To prevent this, they fometimes diminiffi the are at once the moft beautiful, and, in every other current, either by lengthening its eburfe, or by ma- refpedt, the beft contrived. But the moft Angular bridge in Europe is that built king it more winding; or by flopping the bottom with rows of planks, ftakes, or piles, which break the over the river Tave in Glamorganffiire. It confifts current. It is alfo required that thq foundation of of one ftupenduous arch, the diameter of which is bridges be laid at that feafon of the year, when the 175 feet, the chord 140, the altitude 37, and the waters are loweft; and if the ground be rocky, hard abutments 32. This magnificent arch was built by gravel, or ftony, the firft ftones of the fohndation William Edward, a poor coUntry-malbn, in the year may be laid on the furface; but if the foil be foft fand, 1756. Bridges are either built of ftone or timber, as is it will be neceflary to dig till you come to a firm botjudged moft convenient. tom. Among the bridges of antiquity, that built by Tfa- 5r««e-B ridges confift of piers, arches, and hutments, jan over the Danube is allowed to be the moft magni- made of hewn ftone, foraetimes alfo intermixed with, ficent ; it was compofed of twenty arches, of an hun- bricks. dred and fifty feet in height, and their opening from IVooden-BRittGES are compofed of beams and joifts, one pier to another was an hundred and fixty feet: fupported by punchions, well cramped and bound The piers of this fine bridge are ftill to be feen in the together. Danube, being erefted between Servia and Moldavia', RuJhen-BRiDGES are made of great bundles of ruffies, bound faft together, over which planks are laid, and a little above Nicopolis. Among modern bridges, that of Weftminfter, built fattened: thefe are put Over marffiy places, to ferve over the river Thames, may be accounted pne of the for a croffihg ground. fineft in the world: It is forty-four feet wide, a com- Pendent or hanging-Bridges, called alfo philofophical modious foot-way being allowed for paftengers, on bridges, are thofe not fupported by ports or pillars, each fide, of about feven feet broad, raifed above the but hung at large in the air, fuftained only at the two ro^d allowed for carriages, and paved with broad ends or hutments. moor-ftones, while the fpace left between them is fuf- Dr^w-B ridge, one that is faftened with hinges at one ficient to 'admit three carriages and two horfes to go. end only, fo that the other may be drawn up; in a-breaft, without any danger. Its extent from wharf which cafe, the bridge ftands upright, to hinder the to wharf is 1220 Or 1222 feet, being full three hun- paffage of a ditch or moat. dred feet longer than London-bride. The free wa- Flying or floating Bridge, is generally made of two ter-way under the arches of this bridge is eight hun- fmall bridges, laid ene over the other in fuch a mar* dred and feventy feet, being four times as much as ner, that the uppermoft ftretches and runs out, by the free water-way left between the fteflings of Lon help of certain cords, running through pullies placed don-bridge: This difpofkion, ^together with the gen-' along the fides of the under bridge, which puffi it fortlenefs of the ftream, are the chief reafons why no wards, till the end of it joins the place it is intended fenfible fall of water can ever flop, or in the leaft to be fixed on. Vol. I. Numb. 29. ‘ 3 8I Bridges