1844. 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



247 



The arch had thus arrived at the exact dimensions which were proposed by 

 Mr. Rennie. 



An account is then given of the progress of the remainder of the structure 

 the forming of the parapet, the roadway, the approaches, &e., the whole of 

 which were finished on the 18th of June, 1S19, having occupied thirty-three 

 months in construction. The stone used in the hridge, is a brown coarse 

 sandstone, or mill-stone grit, of great durability, from the quarries at Bram- 

 ley-fall, about four miles from the bridge; they were brought down by water 

 to within 120 yards of the work. The price of the stone in the vessel along- 

 side the work, scappled ready for dressing, was 9rf. per cubic foot ; the 

 dressing and setting, exclusive of the cornice and the parapet, cost iUl. per 

 cubic foot, which, with conveyance and mortar, made in the whole \5d. per 

 cubic foot ; the cost of the cornice and parapet walls was about id per cubic 

 foot extra. 



The total quantity of masonry was 80,000 cubic feet, and the entire cost 

 of the bridge, including the toll-house, was £7,530. 



Remarks. — Mr. Rennie concurred in the accuracy of the description of the 

 ' Wellington' Bridge ; it presented an excellent example of theory and prac- 

 tice, not only on account of its strict conformity with the principles of equi- 

 librium, but from the correctness with which the works had been executed, 

 as was evinced by the small subsidence of the arch after the centres were 

 struck. Respecting the theory of the arch, writers were nearly agreed upon 

 the principle established by De la Hire, upon the equilibrium of a loaded 

 chain, or of a series of voussoirs, or wedges, with polished touching surfaces, 

 as shown in his ' Traitu de Mc'canique,' in 1695.- The subject had been 

 variously demonstrated by writers, but witli little effect ; architects were 

 forced to select examples at random, for which no precise rules existed; but 

 any persons on examining the actual state ot an equilibrated arch of solid 

 materials, or of a substantial chain suspended at its extremities by points, 

 would immediately perceive the dilTerence in the curves, or loads on the ex- 

 trados, arising from the want of sensibility in the arch, or in other words, 

 from friction and adhesion. Hitiierto theory had been unable to compre- 

 hend these retarding forces, which had actually been so serviceable to the 

 architect : Verronet was perhaps the first to throw any real light upon the 

 subject ; the experiments that he undertook, on the absolute strength of 

 materials, iu the year 1758, previously to the commencement of the cele- 

 brated bridge of Neuilly,-' and subsequently, those by Gauthey, on the failure 

 of the piers of the church of St. Genevieve,-* at Paris, were very instrumental 

 in the advancement of the art. It was, however, chiefly owing to the good 

 quality of the material, that Perronnet was enabled to surmount the diflicul- 

 ties which arose from the unusual subsidence of the arches, in the bridge of 

 Neuilly. The splaying of the arches, by which a double curvature was given 

 to them, and which had been injudiciously copied iu this country, was 

 neither justified by science nor practice. The results of the French experi- 

 ments were much too slow in reaching this country, and the strength of 

 building materials was but little attended to, until within a recent period. 



In the year 1824, the late Dr. Thomas Young having engaged to contri- 

 bute the article ' Bridge,' to the Supplement of the sixth edition of the ' En- 

 cyclopedia Britannica,' applied to Mr. Rennie, to furnish the particulars of 

 the Waterloo and Southwark bridges, then just completed ; when, finding 

 the data insufficient, Mr. Rennie undertook a series of experiments on the 

 absolute and relative strength of materials, part of which he communicated 

 to Dr. Young, and he subsequently published the whole in the ' Philosophical 

 Transactions,' for 1818." The results were then applied to the calculations, 

 on the lateral thrust of the arches of those bridges, perhaps for the first time 

 in this country, and which were more amply applied afterwards to bridges in 

 general by Mr. Ware, and his tables of the relative boldness of brick, stone, 

 and iron bridges, were valuable accessions to our knowledge on this sub- 

 ject.^ As regarded the friction of arches, Mr. Rennie found that the arch 

 stones of Waterloo and New London bridges commenced gliding, or pressing 

 upon the centres, at angles of from 33° to 31° ; he beUeved that soon after 

 the adhesion of the mortar commenced, the centres would have very little 

 pressure on them, even from stones at an angle of 45". As to the gliding of 

 the arch stones at the haunches, from the pressure of the upper voussoirs, 

 he had never seen an instance of it ; but he bad seen the haunches so much 

 eased from the centres, by the lateral action, exerted in driving the stones 

 into the vertex of the arch, as to allow the lagging, or cross bearers above 

 the ribs, to be taken out. This proved the correctness of the rotative system 

 of voussoirs, as shown by experiment. With respect to adhesion, Mr. Ren- 

 nie had seen its eft'ect on broken arches of considerable magnitude, among 

 the buildings of Rome, and also in the bridge of Alcantara over the Tagus, 

 where the centre arch, of nearly 100 feet span, had been blown up by the 

 French, leaving the adjoining arches and piers, which were upwards of 90 

 feet in height, standing perfectly undisturbed. With respect to the magni- 

 tude of arches, M. Perronet expressed himself confident that arches of 500 

 feet span could be safely executed. The bridge which he proposed to con- 

 struct, over a branch of the Seine, at Melon, consisted of a segment of a 

 circle of 400 feet. The experience he had derived from the length of the 

 primitive radii of the the arches of the bridge of Neuilly, and his experiments 

 on the strength of materials, would appear to justify so bold an experiment. 



-* * TraitiJ de Mecanique.' De la Kire. I2mo. Paris, 1695. 



^ * Decriijtion des projets et de la coustruction des Fonts de NeuilU, de Nantes, d'Or- 

 Ifeaus, &c.' Perronnet. 4to. Paris, 17rt8. 



4 'Coustruction desPonts.' Gautliey. 4to. Paris, 1809. 



4 Vide • Pliil. Trans.,' 1818, p. 118. 



s Vide ' A treatise on Arches and their abutment piers.' Sy Samuel Ware. Svo. 

 Iiondos, 1809. 



Mr. Rennie was of opinion, that with our strong magnesian limestones and 

 hard eranites, arches of larger span than any hitherto built, might be safely 

 constructed. There were numerous examples, both in ancient and modern 

 times, of very large arches. The bridge of Narni, in Italy, of Vielle Bnoude, 

 in France," and of Alcantara, in Spain, by the ancients ; and those of Gignac, 

 and of Castel Veccbio, by the middle ages ; but the most remarkable example 

 of cylindrical vaulting (the remains of which still existed), was the bridge of 

 Trezzo, over the Addu, in the Milanese.' The span was 251 feet over the 

 chord, and 260 feet over the semicircle. The stone beams in the church of 

 the Jesuits at Nismes, and those between the towers of Lincoln Cathedral, 

 the former equal to the segment of an arch of 565 feet span, and the latter 

 to one of 262 feet span, proved how much could be done with materials of 

 small dimensions." In modern times there were examples of bold vaulting 

 in France, in the bridges of Neuilly, Mantes, St. Maixence, and Jena ; in 

 Italy, in the Ponte Sta. Trinita, Turin ; in England and Wales, in the bridges 

 of Llanrwst, of Pont-y-tu-Prydd, of Gloucester, of Chester, and those of Lon- 

 don and Waterloo over the Thames ; independently of numerous arches and 

 viaducts, more recently erected for the use of railways. The radii of curva- 

 ture of the centre arch of New London bridge, taken near the vertex, would 

 equal in boldness an arch of 333 feet ; and the length of the key-stone, at 4 

 feet 9 inches, would make the depth only ^th of the whole span. 



The origin of the arch had occasioned much controversy. The subject 

 had been learnedly investigated by Dutens, Le Roy, King, and others, but 

 apparently to little purpose, as the invention of the arch would now appear 

 to be, with more justice, attributed to the Egyptians, as they seemed to hava 

 used it, many centuries before the Christian era. The researches of modern 

 travellers, particulariy those of Sir Gardiner Wilkinson," proved that the 

 brick arch was known in Egvpt iu the reign of Amenoiph I., 1540 years B.C., 

 and the stone arch in the time of Psamaticus II., COO years b.c. " The most 

 remarkable,'' savs Sir Gardiner Wilkinson, " are the door-ways surroundmg 

 the t-iuks of Assassief, which are composed of two or more concentric semi- 

 circles of brick, as well constructed as at the present day, and all the bricks 

 radiate to a common centre." Mr. lloskins was of opinion that arches were 

 constrncted long anterior to the time of the Ptolemies ; for in the pyramids 

 of Ghebel Hirkel and Dunkalie, which were of more .incient date, both round 

 and pointed stone arches were discovered. Mr. Perring stated that he found 

 at Thebes some remarkably well-formed arches of 12 feet to 14 feet span, 

 built in concentric half-brick rings, the bricks of which were marked with 

 the name of Sesostris ; consequently they were upwards of 3180 years old.'" 

 A representation of the tomb of Saqqura and its arched vault of stone, was 

 given in the vignette of the 10 chapter of the third volume of Sir Gardiner 

 Wilkinson's " Maimers and Customs of the Ancient Egyptians." The arch 

 seemed to have been known to the Etruscans; and from the representations 

 of their palaces and their sea- ports, the arch appeared generally to have been 

 employed for moles and jetties. With reference to the knowledge of the 

 arch among the Greeks, opinions were very contradictory. The researches 

 of modern travellers had brought to light many curious remains of Cyclopean 

 or Pelasgic architecture ; but in confirming the descriptions of the ancient 

 cities of Mycena; and (Jrchomenos, they had left us stdl iu ignorance as to 

 their actual knowledge of the arch. 



Mr. Rennie exhibited a series of lithographic prints, from drawings made 

 by the late Mr. Dodwell during bis travels in Greece. They displayed the 

 various doorways of Pelasgic fortifications, from the lintel of single stones 

 resting on upright jambs, to the overlapping of the stones until they reached 

 each other, in the form of a triangle, as in the gate of the lions, the entrance 

 into the treasury of Atr.-eus, &c. But the most remarkable monument was the 

 subterranean chamber, of which Mr. Dodwell's Uthographic plate gave an 

 imperfect idea ; complete plans and sections of that extraordinary budding 

 were given by Mr, Donaldson in the supplement to the •' Antiquities of 

 Athens,'" ' from which it appeared, to have been constructed in the form of 

 a parabolic cone, of 48 feet in diameter at the base and 44 feet 6 inches in 

 height, by means of rings of regular masonry, overiapping each other until 

 they reached the apex, where the aperture was closed by a flat stone. From 

 this and other buildings of a similar kind, there was reason to infer that the 

 ancient Greeks had very imperfect notions of the arch. Mr. Ivinnaird, in his 



o ine loiiowing umieiiaiuus VI lui; *u... "^ ^- , \_'?j . . J I. 



SpRuin to Mr. Rennie (dated Feb. 27, 1827). "The ancient bridge was constructed by 

 the Romans for the use of foot-passengers, pack.mnles, and smaU carts drawn bjr oxen. 



Metres. English feet. 



Length of the arch ... 66 = '?'?'''?, 



Rre.idth .. . . . 5 = Ib'OUD 



Height ,, . . . IS to 10 = 59-058 to 61-339 



"The arch was a segment of a circle, formed of volcanic stone, of little consistence. 

 The bridge save way in the course of lime, but was upheld for fifteen years, by means ot 

 buttress walls, H metres (= 'Jl-BS English feet) in thickness, and 10 metres (- 32-8 Eng- 

 lish feet) in height ; and also by bars of iron, li.\ed in the wing wall, and through several 

 courses of the arch-stones. The structure finally fell, aud a new stone bridge has been 

 erected upon the same site, of which the following are the dimensioDs;— " 



English feet. 

 Opening of the arch, (which is a semicircle) . 1.5U-9 



Breadth of ditto 24-7 



Height from the stream to the pavement . . B3'7 



7 A section of this arc h is sliown in Part 1 of the " Theory, practice, and architecture 

 of Bridges." Hann and Hosking. 8vo. Woale. London, 1839. 



B Robinson, in his " Travels in Palestine," mentions the remains of an arch over the 

 valley of Kedron, at Jerusalem, supposed to have been 3.^0 feet span. 



o " illauners and Customs of the Ancient Egyptians." Wilkinson. 3 vols. 8vo. 

 Loudon, 1837. 



10 Vide Minutes of Proceedings, Inst. C. E., for 1843, page 170. 



1 1 " Antiquities of Athens," &c. Stewart and Revett, Supplement. Folio. Lon- 

 don, 1830. 



