BRIDGE. 



681 



The arches are segments of circles, seven in num- 

 ber ; the span of the centre arch being 57 feet 9 

 inches, and the rise 10 feet 6 inches. The entire 

 length of the bridge, from centre to centre of newels, 

 560 feet, and from the faces of the abutments 430 

 feet, of which 389 feet are open water-way. The 

 whole breadth of the bridge within the parapets is 

 58 feet, of which 33 form a carriage way, and 12 

 feet 6 inches on each side a footpath, being thus 

 broader than any bridge in Britain. The roadway 

 of the bridge rises one foot in forty-four. By the 

 contract, the bridge is stipulated to be finished by 

 the 3lst December, 1836, and the expense of its 

 construction to be 31,936 15s. 2d. 



Metal Bridges are the invention of British artists. 

 The true elements of their construction are as yet but 

 imperfectly understood. The first bridge of cast- 

 iron ever erected is that over the Severn, about two 

 miles below Colebrookdale, in Shropshire. It is an 

 arch composed of five ribs, forming the segment of a 

 circle. Its chord is 100 feet long, and its height 45 

 feet. It was erected in 1777. The second cast-iron 

 bridge was designed by Thomas Paine, the famous 

 political writer, and was intended to have been taken 

 to America ; but, the speculator failing in his pay- 

 ments, the materials were afterwards used in con- 

 structing the beautiful bridge over the river Wear at 

 Bishop's Wearmouth, in the county of Durham. The 

 chord of the arch is 240 feet long ; the height, 30 

 feet. The Southwark or Trafalgar bridge over the 

 Thames at London is, at present, the finest iron bridge 

 in the world. It.consists of three arches. The chord 

 of the middle arch is 240 feet long, and its height 

 24 feet. There are several other fine bridges of this 

 kind in England. Mr Telford proposed an iron arch 

 of much larger dimensions than any now existing, to 

 take the place of London bridge. The length of the 

 chord was to be 600 feet, ana its height 65. The 

 plan has not been executed. 



Timber bridges. Timber is the most ready, and 

 perhaps the most ancient material used for the con- 

 struction of bridges. The earliest timber bridge on 

 record is that thrown by Julius Caesar over the Rhine, 

 and described in his Commentaries. Germany is the 

 school for wooden bridges, as Britain is for those of 

 iron. The most celebrated wooden bridge was that 

 over the Rhine at Schaflhausen. (See a representation 

 of it in Plate XIV.) This was 364 feet in length, 

 and 18 feet broad. The plan of the architect was, 

 that the bridge should consist of a single arch. The 

 magistrates of the place, however, required that he 

 should make it of two, and use the middle pier of a 

 stone bridge, which had previously stood there. He 

 did so, but contrived to leave it doubtful whether the 

 bridge was at all supported by the middle pier. It 

 was destroyed by the French, in April, 1799. The 

 same architect and his brother have also erected 

 several other fine arched wooden bridges. Several 

 others have been erected, in Germany, by Wiebeking, 

 perhaps the most ingenious carpenter of our times. 

 In the United States of America the Trenton bridge 

 over the Delaware, erected by Burr in 1804, is the 

 segment of a circle 345 feet in diameter. Its chord 

 measures 200 feet ; its height, or versed sine, is 32 

 feet, and the height of the timber framing of the arch, 

 at its vertex, is no more than two feet eight inches. 

 The timber bridge over the Schuylkill, at Philadel- 

 phia, is of the extraordinary span of 340 feet. The 

 versed sine is only 20 feet, and the height of the 

 x. 



wooden framing, at the vertex, seven feet. Its nr- 

 chitect was Wernwag, who built it in 1813. The 

 bridge built by Palmer, over the Piscataqua, near 

 Portsmouth, New Hampshire, in 1794, is the segment 

 of a circle 600 feet in diameter. Its chord line mea- 

 sures 250 feet, its versed sine 27 feet 4 inches, and 

 the height of the timber frame-work of the arch eiglu 

 teen feet three inches. It is put together with 

 wooden keys. The same ingenious mechanic erected 

 two other wooden bridges, one over the Merrimack, 

 at Deer Island, near Newburyport, of 160 feet dia- 

 meter, finished in 1792, and the other over the 

 Schuylkill at Philadelphia, of 194 feet chord, and 12 

 feet versed sine, being the segment of a circle 796 feet 

 in diameter. This was finished in 1803. The old wood- 

 en bridge over the Clyde at Hutchesontown, Glasgow, 

 constructed by Mr Peter Nicholson, was a very fine 

 piece of carpentry, describing from end to end the 

 segment of a circle. Although slim in its construc- 

 tion, it stood the tear and wear of a busy thorough- 

 fare for many years. Near the site where the new 

 Broomielaw bridge has been built, a wooden bridge 

 has been erected as a temporary accommodation for 

 the public. This is a very handsome and efficient 

 construction. It was built with great rapidity, and at 

 a comparatively trifling expense, yet it seems fitted 

 to last many years, and its appearance is pleasing and 

 even picturesque. 



Pendent bridges, or bridges of suspension, although 

 held, by some persons, to be a modern invention, or 

 derived from the rope bridges of South America and 

 the East Indies, were in use in Europe in the time of 

 Scamozzi, as may be seen in his Del Idea Archi, 1615 ; 

 yet the principles requisite to determine the structure 

 of this kind of bridges had not been made public 

 before the time of Bernoulli!. The use of these 

 bridges is of great antiquity in mountainous countries. 

 The most remarkable bridge of suspension in exis- 

 tence is that lately constructed by Mr Telford over 

 the Menai strait, between the isle of Anglesea and 

 Caernarvonshire in Wales. It was finished in 1825. 

 The roadway is 100 feet above the surface of the 

 water at high tide. The opening between the points 

 of suspension is 560 feet. The platform is about 

 thirty feet in breadth. The whole is suspended from 

 four lines of strong iron cables by perpendicular iron 

 rods, five feet apart. The cables pass over rollers 

 on the tops of pillars, and are fixed to iron frames 

 under ground, which are kept down by masonry. 

 The weight of the whole bridge, between the points 

 of suspension, is 489 tons. There are several other 

 bridges of suspension in Great Britain. In 18 1, a 

 chain-bridge, 1000 feet long, was' projected by Mi 

 Telford, to cross the Mersey at Liverpool, but it has 

 never been executed. In the United States of Ame- 

 rica, such bridges are to be found, though not of the 

 dimensions of the British. That over the Merrimack, 

 at Newburyport, is a curve whose chord measures 

 244 feet. That over the river Brandywine, at Wil- 

 mington, has a chord of 145 feet ; that at Browns- 

 ville, over the Monongahela, measures 120 feet be- 

 tween the points of suspension. Another, in its 

 vicinity, forms an inverted suspended arch, with a 

 chord of 112 feet. Besides these there are some 

 others. 



The following remarks on the construction of 

 bridges are from Bigelow's Technology, (Boston, 

 . 1829) : The construction of small bridges is a simple 

 process, while that of large ones is, under certain 



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