The second iron bridge, of which the particulars have come to our knowledge, was that designed by Mr. Thomas Paine, author of many political works. It was constructed by Messrs Walkers, at Ro therham, and was brought to London, and set up in a bowling green at Pad dington, where it was exhibited for some time. After which it was intended to have been sent to America ; but Mr. Paine not being able to defray the ex pense, the manufacturers took it back, and the malleable iron was afterwards worked up in the construction of the bridge at Wearmouth The third iron bridge of importance erected in Great Ili itain was that over the river Wear, at Bishop Wearmouth, near Sunderland, the chief projector of which was Rowland Burdon, Esq. M. P. This bridge consists of a single arch, whose span is 236 feet ; and as the springing stones at each side project two feet, the whole opening is 240 feet The arch is a segment of a circle, of about 444 feet diameter, its versed sine is 34 feet, and the whole height from low water about 100 feet, admitting vessels of from two to three hundred tons burden to pass un der, without striking their masts. A se ries of one hundred and five blocks form a and six of these ribs compose the breadth of the bridge. The spandrels, or the spaces between the arch and the road-way, are filled up by cast iron cit. des, which touch the outer circumfer ence of the arch, and at the same time support the roadway, thus gradually di minishing from the abutments towards the centre of the bridge. There are al so diagonal iron bars, which are laid on the tops of the ribs, and extended to the abutments, to keep the ribs from twisting. The superstructure is a strong frame of timber, planked over, to support the car riage-road, which is composed of marl, lime-stone, and gravel, with a cement of tar and chalk immediately upon the planks, to preserve them. The whole width of the bridge is 32 feet. The abut ments are masses of almost solid masonry, 24 feet in thickness, 42 in breadth at bot tom, and 37 at top. The south pier is founded on the solid rock, and rises from about 22 feet above the bed of the river. On the north side the ground was not so favourable, so that it was necessary to carry the foundation DI feet below the bed.
The weight of the iron in ibis extraordi. nary fabric amounts to 260 tons ; 46 of these are malleable, and 214 cast. The entire expense was 27,0001.
The splendid example of the bridge at Wearmouth gave an impulse to public taste, and caused an emulation among ar tists, which has produced many examples, and more projects of iron bridges. The Coalbrook Dale Company have construct ed several, among which is a very neat one over the river Parrot, at Bridgewater. Mr. Wilson, the engineer employed by Mr. Burdon, has also built several, and some years since finished a very elegant one over the river Thames, at Staines, which is by far the most complete in de sign, as well as the best executed, of any that has hitherto been erected. This bridge consists of a single arch, 181 feet in span, and 16 feet 6 inches in rise, being a segment of a circle of 480 feet. The blocks of which the ribs are composed are similar to thdse in the Wearmouth bridge, except that these have only two concentric arcs instead of three, as at the latter. The arcs are cast hollow, and the block connected by means of dowels and keys; thus obviating the great defect ob served at Wearmouth, of having so much hammered iron exposed to the action of the air. Four ribs form the width of the arch, which are connected together by cross frames. The spandrels are filled in with circles, which support a covering of iron plates an inch thick: on this is laid the road-way, 27 feet wide. Two hundred. and seventy tons is the weight of the iron employed in the bridge, and three hun dred and thirty of the road-way.
Public bridges, which are of general conveniency, are of common right to be repaired by the inhabitants of that county in which they lie. Where a man makes a bridge for the common good of the King's subjects, he is not bound to repair it. No one can be compelled to build, or contribute to the charges of building any new bridge, without act of parliament: and if none are bounden to repair by tenure of prescription at common law, then the whole county or franchise shall repair it.