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Britain and Ireland . In the latter kingdom, we cannotrefrain from noticing the bridge over the Liffey , aboveDublin , called Sarah, or Island Bridge, build in the year1792, by Mr. Alexander Stevens, a mason of Edinburgh .It consists of a single elliptical arch, 106 feet wide, risingonly 22 feet; and is consequently six feet wider than theRialto, at Venice, and one foot less in altitude. The city ofDublin has likewise five other bridges over the Liffey ,of which the two following are particularly worth notice:Arran , or Queen’s Bridge, originally erected in the year1684, but being destroyed by a flood in 1763, was rebuilt ofhewn stone, and finished in 1768. It is built in a handsomelight style, and consists of three arches, with paved ban-quettes for foot-passengers, on each side of the carriage-way,guarded with stone balusters. The other is Essex Bridge,first built in 1681, taken down in 1753, and rebuilt after themodel of Westminster Bridge. It has five arches, thebuttresses between which, support semicircular niches, pro-jecting from the parapet; between these niches are balus-trades, which are continued to the ends of the bridge. Thefoot-ways are flagged, and the whole is constructed of hewnstone, in very fine taste.

We come now to those magnificent examples of bridge archi-tecture, equalling any that the Romans have left, and surpass-ing all others in the world—the bridges of London . Eachof these noble structures maybe considered almost perfect in itskind, and as affording a specimen of the application in its gran-dest form, of the peculiar material of which it is constructed.

Four of these fine bridges are built of stone—namely,London Bridge , Blackfriars Bridge, Waterloo Bridge, andWestminster Bridge. They will be fully described underStone Bridge. Southwark Bridge, built of iron, underIron Bridge. And the beautiful new bridge lately com-pleted at Ilungerford, by Brunei , the celebrated engineer,under Suspension Bridge.

Among Bridges of Wood, (for the principles and methodsof constructing which, see Timber Bridge, ) the first thatattracts our notice is the bridge of Cassar across the Rhine .It consisted of a double row of piles, leaning to the course ofthe stream, and joined together at the distance of two feetfrom each other. Forty feet lower down the river, wasanother double row of piles, leaning against the stream, andtowards the former row. Between the double piles, whichwere well rammed into the bed of the river, long beams, twofeet thick, were placed, and held fast at each end by twobraces. These beams being joined by transverse pieces, thewhole was surmounted with hurdles. To preserve this struc-ture from injury by the force of the water, the supporters wereguarded with piles as buttresses; and above the bridge, otherpiles were placed, to stop the progress of trees or timber,which by accident might fall into the river, or be designedlyfloated down by an enemy, to destroy the work.

The bridge over the Cismone, a river falling from themountains which separate Italy from Germany , is describedby Palladio as an interesting object to the builder and architect.The river where this bridge is erected is 100 feet wide; andbecause the current is very rapid, and great quantities oftimber are floated down it by the mountaineers, the bridgewas constructed of a single span. The width is dividedinto six equal parts, and at the end of each part, except atthe banks, which are strengthened with pilasters of stone, areplaced the beams that form the breadth of the bridge. Onthese, leaving a little space at their ends, other beams areplaced lengthwise, constituting the sides. The king-postsare disposed on either side, over both beams, connected withthe projecting ends of those forming the breadth, by meansof iron bolts and pins.

At Wittengen, in Switzerland , is a very curious bridge,the contrivance of Ulrick Grubenhamm, an uneducated car-penter of Tuffen, in the canton of Appenzel, celebrated forseveral works of the same nature. It consists of two woodenarches parallel to each other, with the roadway hangingbetween them. The span is 230 feet, and rises only fivefeet. The arches approach the catenarian shape, and arebuilt of seven courses of solid oak logs, in lengths of 12 or14 feet, and 16 inches and upwards in thickness. Bypicking these logs of a natural shape suited to the intendedcurve, the wood is nowhere trimmed across the grain. Thelogs being laid one upon the other, with their abutting jointscarefully alternated, have the appearance of a wooden wall:instead of being pinned together, they are surrounded withstraps of iron, at every distance of five feet, and fastened bybolts and keys. The abutments are the natural rock. Theroad-way intersects these arches at about the middle of theirheight, and is supported by cross joists, resting on a longhorizontal beam, connected with the arches on either side byuprights bolted into them. Three of the spaces betweenthese uprights have struts or braces, giving the upper worka sort of trussing in that part. The whole is covered with aroof, projecting over the arches on each side of the roadway,to defend the timbers from the injuries of the weather. Thisbridge is of more than sufficient strength to bear any loadthat can be laid upon it, though the attempt to truss the endsdemonstrates that the builder was ignorant of true architec-tural principles.

In 1754, Grubenhamm erected another bridge, upon a plannearly similar to the foregoing, at Schaffhausen , where theriver (the Rhine ) is nearly 390 feet wide. The current isvery rapid at this spot, and had destroyed several stone,bridges, when Grubenhamm offered to throw a woodenbridge across, of a single span ; but the magistrates werealarmed at the proposition, on account of the breadth of theriver, and would scarcely listen to it: at last they consentedthat he should build a bridge, provided he would divide itinto two spans, and use the middle pier of the late stonebridge as a support at their junction. Grubenhamm compliedwith the wish of the magistrates, so far as to divide his bridgeinto two unequal parts, the span of the one being 172 feet,and of the other, 193, both appearing to rest upon the oldpier, though he contrived to leave it doubtful whether theyreally did so or not. This structure cost £8,000 sterling, andtravellers inform us, that though it sustained the most heavilyladen waggons in perfect security, yet the weight of a singlefoot-passenger caused it to tremble under him. It wasdestroyed by the French, when they evacuated Schaffhausen ,in April, 1799.

Among wooden-bridges, the Schuylkill bridges at Philadel'pliia, in America , are very remarkable.

Wooden-bridges, unsupported by posts or pillars, and sus-tained only by butments at the ends, have obtained the deno-mination of Pendent or Hanging Bridges, by some also calledPhilosophical Bridges, of which Palladio has described threemodes of erecting; such is the bridge over the Cismone,already described. Doctor Wallis has likewise given thedesign of a timber bridge, 70 feet long, without any pillars,which may be useful where supports cannot be convenientlyerected; and Doctor Plott assures us, that formerly there wasa large bridge over the castle ditch at Tutbury, in Stafford'shire, made of short timbers, none of them above a yard inlength, yet not supported from beneath, either by pillars orarches. The Spaniards use bridges of this kind for crossingthe torrents of Peru , over which it would be difficult, not tosay impossible, to throw more solid structures, either of woodor stone. Some of these hanging-bridges are sufficiently strong