Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/387

355&#93; BRI ■piers of tills vast structure still re- main. Among modern bridges, that built over the Thames at West- minster may be considered as one of die most magnificent in the world; it consists of 13 large and two small arches, together with i4 intermediate piers : the two mid- dle piers are each 1 / feet in thick- ness at the commencement of the arches > and contain 3000 cubic feet, or near 200 tons of solid stone : the middle arch is "6 feet wide. Blackfriars bridge is also an ex- ceedingly light and elegant struc- ture ; it contains nine large arches of an elliptical form ; the central arch being 100 feet wide. vVe cannot injustice avoid men- tioning the patriotic efforts of Mr. Burdon, member for Durham, who in 1 792 obtained an. .aft . for the erection of. a bridge across the river Wear, near Sunderland. This structure is of cast iron, and con- sists of six ribs, at five feet distance from each other : the spandrils are composed of cast iron circles. The six ribs wese put together over the river in the short space of ten days. The superstructure is 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 upon the planks, to preserve them : the whole width of the bridge is 32 feet, and the arch is supposed to weigh upwards of 900 tons, of which 2 GO are iron. This magnificent structure is erected on improved principles, yet differing from those adopted by the Colebrook-Dale Company. Al- though adhering to the ancient con- struction of bridges, by the subdivi- sion of the parts of the arch, in the manner of key-stones, Mr. Bur- don took advantage of the ducxi- B R 1 Gag iity and tenacity of iron, to produce an arch cf that metal, at least fir-" teen times lighter than a corres-' ponding arch of stone, and most easily put togetiier. The expence of constructing this bridge amounted to 26,0001. the whole of which, except 40001. was furnished by Mr. Burdon. This gentleman, in 1/95, also obtained a patent for his invention of the manner of making and applying cast iron blocks, to be substituted in lieu of key-stones, in the con- struction of arches, which blocks, tubes, &c. he employed in the bridge above-mentioned. A patent was granted to Mr. Nash, of Dover-street, in 1797, for an invention somewhat similar to that above-mentioned. He pro- vides hollow masses of cast or wrought iron, which are to be filled with earth', sand, &:c. and have the appearance of solid bodies. Ac- cording to this plan, the arch of the bridge is formed by hollow frames, or boxes, each consisting of four sides and a bottom. These boxes, after being properly arranged in the manner stated by the pa- tentee, are then to be filled with sand, stones, &c. by which means the arch, becomes like one solid body cased with iron. A farther explanation of this invention may be seen in die 6di volume of the Repertory of Arts and Manufac- tures. The latest patent for bridges, was that granted in June 1800, Uj Mr. Samuel Wyatt, of Chelsea College, for his invention of a new method of constructing bridges, warehouses, &rc. without the use of wood, as a constituent part. The principle of his discovery consists in the combination of pipes, tubes, or hollow pieces of cast iron, in a A a 2 longitudinal