BRIDGE. 



tir.g. Tia\ filers inform us, that it Hiook if a man pafied ovo- 

 it i yet waggons heavily laden alfo went over it without 

 dang.-r. We are forry to add, that this curious bridge was 

 bu.-'jt by the French when they evacuated SchafThaufen, in 



April I7v9- 



Bel'dcs tlie woodenbrid^rfsalreadydtfcribcd, there are fcve- 

 ral tlcijaiit and well conllruCled edifices in Great Britain : 

 t'le molt eminent of which was that at Walton-upon-Tliamcs. 

 'I'hii bridge coiifirlcd of three wooden arches, and five brick 

 arches at each end ; the middle arch was 130 feet in fpan, 

 with a rife of 28 feet, conllruftid of three principal ribs, 

 framed in the manner reprefented in PlaU XXXIV. of 

 yfirl'i/fffurf. It was the dcfign of the ingenious carpenter, 

 Mr. Etheridge. 



/rin Brh.'jes. Iron beinjj the mod abundant, cheap, and 

 pcin.-ral!y ufcful of all mitals, has of late been employed in 

 ni.uiy works where great (Irength was required in proportion 

 to the weij;ht of the material : hence cylinders, beams, and 

 pumps for llcam-engines, boats, and barges for canals and 

 navigable rivers, beams and pillars for warehoufcs and other 

 large buildings, and at length bridges, have been conllruded 

 of iron. 



Iron bridges are the exchifive invention of BritiH) artitls. 

 The firll that has been eretled on a large fcak- is tliat over 

 the river Severn, at Coalbrook Dale, in Shroplhirc. This 

 bridge is compofcd of five ribs, and each rib of three con- 

 centric a'cs connefted together by radiating pieces. The 

 interior arc fonns a complete femiclrcle, but tiie otliers ex- 

 tend only to the cills under the roadway. Thcfe arcs pafs 

 through an upright frame of iron at each end, which fervcs 

 as a guide ; and the fmall fpace in the haunches between 

 the frames and the outer arc is filled in with a ring of about 

 fevcn feet diameter. Upon the top of the ribs are laid call 

 ir.in plates, which fuftain the roadway. The arch of this 

 bridge is 1V> feet 6 inches in fpan ; the interior ring is call 

 in two pieces, each piece being about 70 feet in length. It 

 was contlrudcd in tiie year 1779, by Mr. Abraham Darby, 

 iron-mallcr at Coalbrook Dale, and mull be confidercd as a 

 very bold effort in the firll inttance of adopting a new mate- 

 rial. The total weight of the metal is 3 /SI tons. 



The fecond iron bridge, of which the particulars have 

 come to our knowledge, v. as that dtfigned by Mr. Thomas 

 Payne, author of many political works. It was conllrufted 

 bv MtlTrs. Walkers at Rotherham, and was brought to Lon- 

 don, and fet up in a bowhng-grcen at Paddington, where it 

 was exhibited for fome time. After v.iich it was intended 

 to have been fent to America; but Mr. Payne not being 

 sble to defray the c.xpence, the manufailurers took it back, 

 and the malleable iron was afterwards worked up in the 

 conftruction of the bridge at Wearmouth. 



The third iron bridge of im.pnrtance erefted in Great 

 Britain, was that over the river Wear, at BiP.icp Wear- 

 mouth, near Sunderland, the chief pro;e<3or of which was 

 Jlowland Burdon, cfq. M. P. As this is i- the moll confi- 

 dcrable tlruclurc of the kind, it may be proper to give a 

 brief iltetch of iti hiftor)'. In confequcnce of the increafing 

 trade and population of Sunderki.d and the two Wtar- 

 mouths, tlie ancient ferry, which v/as almolt in tl:e middle 

 of tlie harboar, had become very infnfficicnt and unfafe, fo 

 that, befides frequent delays and difappointments, feve- 

 rul inttances had occurred of the lofs of lives. About the 

 year 17^0, in which Mr. Biirdon v.as returned to parliament 

 by the county of Durham, foTie gcntlemrn iutereded in the 

 welfare of the town and neighbourhood of Sunderia[;d, 

 united for the purpofe of removing th.e evilr. ariling from the 

 ferry, and Mr. Burdon wa< appointed oie of the committee. 

 L'oiicciving at -firft that a ihjne bridge would he proper, they 

 b«gan to adopt m.cafurcs for its ereclion. An archiie£i was 



chofen to carry on the neceffiuy works, who in due time 

 produced plans, cllimatcs, and a model of the intended edi- 

 fice. But as the work was of confiderable magnitude and 

 importance, it was thought expedier^ to refer the defign to 

 the opinion of fome gentlemen of celebrity for fcieiitihc and 

 praftical knowledge in and near the metropolis ; their report 

 being unfavourable, the fchemc of ereClmg a Hone bridge 

 was "abandoned. The committee, however, being now 

 warmly engaged in the bufinefs, continued to prolecutc 

 their inquiries ; and Mr. Burdon in particul.ir being fre- 

 quently called by his parlianientaiy duty to London, wjs 

 verv diiio'ent in his endeavours to obtain inform.ation ai;d 

 hints from various quarters, as to the- peculiar advantages 

 and difadvantngcs of different materials, as well as of 

 various modes of condrudlion. Mr. Burdon had the good 

 fortune to be alTifted in the maturing of his plans by 

 Mr. Thomas Wilfon, a truly ingenious man, and at tiie 

 fame time to learn much of the conflruction of iron 

 bridges from MefTrs. Walkers, of Rotherham, fo that at 

 length he became pcrfuaded that iron would be the mcfb 

 proper material of which to form the propoied bridge. 

 He tho>!ght it bell, however, to adhere to the ancient 

 conftruclion, by dividing the arch into portions in the man- 

 ner of arch ftones, and taking advantage of tl;e duftility 

 and tenacity of iron to produce an arch of that metal at 

 leall fifteen times lighter than a corresponding arch of Hone, 

 and capable of being put together upon an ordinary fcallbld- 

 ing. inllead of an accurate centre, ina nuich fhorter fpace 

 of ume. 



Mr. Wilfon, in conjunftion with MefTrs. Walkers, con- 

 llrufted and fet up an experimental rib at Rotherhrmi, which 

 being found to anfwer expeftation, the lucccfs of the expe- 

 riment was communicated by Mr. Burdon to the towTi of 

 Sunderland and the county ; and his propofition for the 

 ereition of an iron bridge was acceded to. The firft Hone 

 was bid in September, 1795 ; and Mr. Wilfon was ap- 

 pointed to the fuperintendance of the work. The iron-work 

 was cad by MefTrs. Walkers, of Rotherham, and tlie arch 

 was turned upon a very light but firm fcafiolding, fo judi- 

 cioufly conllrufted that not any interruption was given to 

 the pafTage of the numerous vefTcls which navigate the 

 bufy river of Sunderland. The mode of bracing the ribs 

 was fo fimple and expeditious, that the whole was put 

 together and thrown over the river in ten days ; the fcaf- 

 folding was immediately removed, and the bridge opened 

 for general ufe or. the 9th of Augull, 1796. 



During the period occupied in erefting the bridge, 

 Mr. Burdon took out a p itent to I'ecure the invention 

 of " a certain mode or manner of makii'g, uniting, and ap- 

 plying caft iron blocks to be fubllicuted in lieu of 

 key-Hones, in the conilruftion of arches." He thus pro- 

 ceeds to defcribe his invention, which " confills in apply- 

 ing iron or other metallic compontions to the purpoTe of 

 conllrufting arches upon the fame principle as flor.e is 

 now employed, by a fubdivifion into blocks eafily port^ible, 

 anfwcring to the key-flones of a common arch, which 

 being brought to bear on each othtr gives them all ihe 

 firmr.efs of the folid fione arch, whiKl, by the great va- 

 cuities in the blocks, and their refpcftive diflances in tlitir 

 lateral polition, the arch becomes much lighter than that 

 of flnne, and by the tenacity of t!ic nictal the parts are 

 fo intimately cur.nefted that the accurate calculation of the 

 extrados and intrados, fo neceflary in ftone arches of mag- 

 nitude, is rendered of much lefs confequcnce. /Vj-. 4. P/,je 

 XXXIII. oi ArclAttilurc reprefentsa block of catt iron, five 

 feet in depth from A to A, and four inches in thickncfs, hav. 

 ing thret arms B, B, B, and making a part of a circle or ellip. 

 fiji the middle arm is two feet in length from D to C, ai;d 



the 



