But the most extraordinary bridge in Great Britain, is that over the Taff, near Elantrissent, in Glamorganshire, called by the Welch Ponty-ty-Pridd. It is the work of William Edwards, an uneducated mason of the country, who engaged, in 1740, to erect a new bridge at this place, which for elegance of design, and neatness of execution, surpasses any thing of the kind throughout the Principality. The description ! and history of the progress of this bridge, we shall borrow from Mr. Malkin's Tour in South Miles : "It consisted of three arches, elegantly light in their construction. The hewn stones were excellently well dressed and closely jointed. It was admired by all who saw it. But this river runs through a very deep vale, that is more than usually woody, and crowded about with mountains. It is also to be considered, that many other rivers, of no mean capacity, as the Crue, the Bargoed Taff, and the Cunno, besides almost numberless brooks, that run through long, deep, and well-wooded vales or glens, fall into the Taff, in its progress. The descents into these vales from the mountains being in general very steep, the waters, in long and heavy rains, collect into these rivers with great rapidity and force, raising floods, that in their description would appear absolutely incredible to the inhabitants of open and flat countries, where the rivers arc neither so precipitate in their courses, nor have hills on each side to swell them with their torrents. Such a flood unfor tunately occurred soon after the completion of this under taking, which tore up the largest trees by the roots, and carried them down the river to the bridge, where the arches were not sufficiently wide to admit of their passage : here therefore they were detained. Brush-wood, weeds, hay, straw, and whatever lay in the way of the flood, came down, and collected about the branches of the trees, that stuck fist in the arches, and choked the free current of the water. In consequence of this obstruction, a thick and strong dam was formed, and the aggregate of so many collected streams being unable to get any farther, the waters rose to a pro digious height, and by the force of their pressure carried the bridge entirely away ! Edwards had given security for the stability of his bridge during the space of seven years; it had stood only about two years and a half; of course he was obliged to erect another, and he proceeded on his duty with all possible speed. The second bridge was of one arch, for the purpose of admitting freely under it whatever incum brances the floods might bring down. The span or chord of this arch was 140 feet ; its altitude 35 feet ; the segment of a circle, whose diameter was 170 feet. The arch was finished, but the parapets were not yet erected, when such was the pressure of the unavoidably ponderous work over the haunches, that it sprang in the middle, and the key-stones were forced out ! This was a severe blow to a man, who had hitherto met with nothing hut misffirtune in an enterprise which was to establish or ruin him in his profession. William Edwards, however, possessed a courage which did not easily forsake him ; he engaged in it a third time, and by means of cylindrical holes through the haunches, so reduced their weight, that there was no longer any danger to be appre hended. The second bridge fell in 1751 ; the third, which has stood ever since, was completed in 1755." The breadth of this bridge is about 11 feet in the widest part; but in order to strengthen it horizontally, it is eontracted towards the centre by seven offsets, so that the road-way is there one foot nine inches narrower than at the extremities. It consists of a single arch, 140 feet in width, forming die seg ment of a circle of 175 feet ; its height is 35 feet. This arch is between 40 and 50 feet wider than that of the cele brated Rialto, at Venice, and its additional altitude only in proportion. In each haunch are three cylindrical openings running quite through. from side to side, like circular win dows: the diameter of the lowest is nine feet ; of the middle one, six feet ; and of the uppermost, three feet.
Besides the bridges already mentioned, there are other neat and elegant structures in various parts of Great Britain and Ireland. In the latter kingdom, we cannot refrain from noticing the bridge over the Liffey. above Dublin, called ,.s'oroh, or Island Bridge, built in the year 17:12, by 2\1r. Alexander Stevens, a mason of Edinburgh. It consists of a single elliptical arch. 100 feet wide, rising • only 22, feet : and is consequently six feet wider than the Rialto, at Venice, and one foot less in altitude. The city of Dublin 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 year 1GS1, but being destroyed by a flood in 176'3, was rebuilt of hewn stone, and finished in 1708. It is built in a handsome light style, and consists of three arches, with paved ban quettes for loot-passengers, on each side of the carriage-way, guarded with stone balusters. The other is Essex Bridge, first built in 10S1, taken down in 1753, and rebuilt after the model of Westminster Bridge. It has five arches, the buttresses between which support semicircular niches. pro jecting from the parapet ; between these niches are balus trades, which are c011tilillvd to the ends of the bridge. The foot-ways arc flagged, and the whole is constructed of hewn stone, in very fine taste.
We come now to those magnificent exam ples of bridge archi tecture, equalling any that the 1:0111:111s have left, and surpass ing all others in the worb I—the bridges of London. Each of these noble structures may lie considered almost perfect in its kind, and as Ai 'riling a specimen of the application in its gran dest firm, of the peculiar material of winch it is constructed.
Four of these fine bridges are built of stone—namely, London Bridge, Blackfri:irs Bridge, Waterloo Bridge. and Westminster Bridge. They will lie fully described under STONE Baines. Southwark Bridge. built of 'rim, under IttoN IliIitcie. And the bt.antiful new bridge lately com pleted at I I InTerford, by 11rnnel, the celebrated engineer, under 81'SPENSION BRIDGE.
Among _Bridges of if (for the principles and methods of constructing which, see TIMBER 131111)0 e.) the fii'st that attracts our notice is the bridge of Caesar across the Rhine. It consisted of a donlde row 1 piles, leaning tO the course of the stream, and joined together at the distance of two feet from each other. Forty feet lower down the river, was another double row of piles, leaning against the stream, and towards the former row. Between the double piles, which were well rammed into the bed of the river, long beams, two feet thick, were placed. :11111 held fast at each end by two braces. These beams being joined by transverse pieces, the whole was sunlit Hinted with hurdles. To preserve this struc ture from injury by the force of the water, the supporters were guarded with piles as leatresses; and above the bridge, other piles were placed, to stop the progress of trees 01' timber, which by accident might 1:111 into the river, or be designedly floated down by an enemy, to destroy the work.
The bridge over the Cismone, a river from the mountains which separate Italy from Germany, is described by Palladio as an inten.stingoltject to the builder and architect. The river where this bridge is erected is 100 feet wide ; and because the eurrent is very rapid, and great quantities of timber are floated down it by the mountaineers, the bridge was constructed of a single span. The width is divided into six equal parts, and at the end of each part, except at the banks. which are strengthened with pilasters of stone, arc placed the beams that form the breadth of the bridge. On these, leaving it little space at their ends, other beams are platted lengthwise, constituting, the sides. The king-posts are disposed on either side, over both beams, connected with the projecting ends of those forming the breadth, by means of iron bolts and pins.