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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[June, 



at Alcantara, the Pons Palatinus or Ponte Rotto upon the Tiber at Rome, 

 the ruins of Augustus's Bridge at Narai, are cases in point, and every ca- 

 thedral chapter-house in England in the pointed style of architecture, and 

 every arcaded cloister, furnishes another instance to the same effect. 



Another question may arise as to the sufficiency of the area of the bearing 

 surface upon the piers at the springings of the arches, for very much less is 

 allowed than it has been usual to give in such cases. 



Perronet calculated upon experiments, that the stone of which his Neuilly 

 Bridge was built, is capable of sustaining twelve times the weight imposed 

 upon it in the piers of that bridge. The area of the bearing surface of the 

 piers of Neuilly Bridge, is about one-tenth of the area covered by the two 

 half arches resting upon the piers respectively. In the supposed case, the 

 weight of the superstructure, as compared with Perronet's, is diminished by 

 the introduction of the perforation in the arches, longitudinally of the 

 bridge, and the stone of which London Bridge is built, being stronger than 

 the stone used by Perronet, in a much greater degree than the difference of 

 their specific gravities would indicate ; the substance of the arches built of 

 the stronger stone, may be relatively reduced. These circumstances operate 

 to such an extent, that the weight of the superstructure is reduced as coin- 

 pared with Perronet's work, nearly, if not quite, one-fourth ; and as twelve 

 times the sufficient strength is, besides, very much more than enough for the 

 extremest contingencies, it is not too much to assume that the area of bear- 

 ing surface of the arches at the springings, or on the piers, may be taken at 

 one-fifteenth the area covered by the two half-arches. In justification of 

 this assumption, it may be added that, without the same reason for it, but 

 with flatter arches, certainly, than at Neuilly, Perronet made the area of the 

 bearing surface upon the piers at the springings of the arches in the Bridge 

 of St. Maxence, and with the same stone of Saillanconrt. less than one- 

 seventeenth the area in horizontal section of the space, covered by two half 

 arches. 



But the granite used in L ondon Bridge, is of considerably more than 

 twice the strength of the Saillancourt freestone in the bridges of Neuilly 

 and St. Maxence, and upon which Perronet's experiments were made ; and 

 therefore the area of the bearing surface of the arches at the springings, may- 

 be one-thirtieth the area in horizontal section of the space covered by the 

 two half arches resting upon any pier. 



This is the proportion allowed in the case supposed, and the area of bearing 

 face is upon the calculations regarding Neuilly Bridge, and having reference 

 to the different powers of resistance of the two kinds of stone, more than 

 enough for ten times the load it would be called upon to bear. Having re- 

 ference, however, to other instances of the powers of stone to resist crush- 

 ing piessure in the central pillars of some of the cathedral chapter houses, it 

 may he safely concluded that experiments upon small pieces of stone give 

 results much within the strength of the material in the block ; so that having 

 counteracted the tendency of the traffic upon a bridge, to induce vibration in 

 the structure by the introduction of the deep transverse arch, groined to the 

 flat longitudinal arches ; it is believed that the bearing surface at the 

 springings of the arches, and consequently, the piers under them, might he 

 reduced, not merely with perfect safety, but with great advantage, very much 

 beyond what he had now endeavoured to justify, in the example before the 

 meeting. 



Mr. Hosking then proceeded to explain the advantages of corbelling out 

 the parapets on bridges, according to the method he has proposed in his 

 treatise on Bridges ; and read some passages in explanation of them, from 

 that work : and showed, by diagrams, the manner in which the work might 

 be composed constructively, and as to decoration, either plainly corbelled 

 or enriched faces to the parapet. He then resumed his remarks, and 

 stated that in closing his observations upon the design and arrangement of 

 bridges, he could not avoid noticing a pressing instance of an important 

 work, within the personal knowledge of all who live in, or have ever visited 

 London, rendered by circumstances which have grown up around it, alto- 

 gether unfit, both in its design and arrangement, for the position it occupies. 

 In September last he wrote, in the Treatise on Bridges, as follows : — 



" It is difficult to close a Treatise on Bridge Architecture, w ithout remark- 

 ing the increased unfitness of the present superstructure of Westminster 

 Bridge. The arches spring at a level very little above that of low water, 

 where the tide rises and falls from 15 to 18 feet, so that the water-way is 

 nearly 50 feet, or about one-sixteenth less at the height of ordinary spring 

 tides, than at the level of low water in the river. The arches contract the 

 way for navigation much more than it is at all necessary they should, even 

 upon the present piers, and there is more than twice the height from the 

 soffits of the arches to the level of the roadway, than there need be ; the 

 parapets are alike offensive, by their great height from the roadway, and by 

 their ugliness in detail, and injurious by the drafts induced by the perforations 

 of the balustrades ; and the solid counterfort buttresses over the cutwaters, 

 and their inclosed and cupolated heads, add needlessly to the weight upon 

 the piers. The bridge is unfortunately near to the magnificent buildings of 

 the Houses of Parliament, and its great height renders this proximity more 

 injurious than it might otherwise be. In all probability some abatement will 

 be made of the height of the bridge in the process of the works now (1842) 

 in hand for securing the pier, and doubtlessly the same good sense which 

 Opened a view of the river from Blackfriars' Bridge will open the magnificent 

 prospect Westminster Bridge can command, by substituting parapets, which 

 shall be truly so, for the perforated walls which now hedge in the road-way ; 

 but the arches will still continue to render the navigable water-way narrower 



and more inconvenient than even the multiplicity and thickness of the piers, 

 or the condition of the work, impose. The character of the work, too, will 

 still remain inconsistent with its position at Westminster. It ought, therefore, 

 to be completely remodelled. As the piers are now in process of being re- 

 paired and secured, and so as to be free from any danger, founding new piers 

 is out of the question, and the piers cannot be reduced in number without 

 imposing additional weight on those which may be left ; a condition which 

 the original defective foundging, and the badness of the original structure, 

 forbid. The whole of the superstructure might be removed, however, and 

 the piers being carried up from the level of the present springing to that of 

 high water, of the substance which the cutwaters now show within that 

 range, flat pointed arches might be sprung at that level, and the whole 

 superstructure re-constructed in accordance with the prevailing style of the 

 Abbey, Hall, and Palace of Westminster. The longitudinal central groining 

 hereinbefore proposed might well he adopted with excellent effect, lightening 

 the upper works, relieving the thrust of the arches, and greatly economizing 

 the reconstruction, as the old stone would work in well for this purpose, 

 whilst the faces and main vaults were of new. The widening of the water- 

 way by the removal of the springings of the arches out of the water would 

 allow characteristic abutments to occupy the space now taken up by the two 

 first arches of the series of thirteen, as well as the site of the two small land 

 arches, without affecting the current injuriously; and as the flat pointed 

 arch would give much more freedom to the navigation than the semi-circular 

 arch affords, independently of the increased lateral space in every bay, the 

 vertical head-way might be taken at an average of that now afforded by the 

 central group. Moreover, the increased space at the approaches obtained 

 by obliterating the useless land arches would allow the accesses to the 

 bridge from the low ground on either side to be greatly improved, and the 

 ascent eased by dividing tbem to the right and left over the abutments, ami 

 so to disrtibute the rise over a longer space, and give the means of dividing 

 the going and coming traffic. 



These observations, continued Mr. Hosking, coincide in a very remarkable 

 degree, with those upon the same bridge, in the report lately presented by 

 Mr. Harry, to the Commission on the Fine Arts, in connexion with the 

 Houses of Parliament. It was true that his suggestions stood alone in the 

 particulars in which it was almost certain they would be peculiar ; as it 

 regards the introduction of the inner transverse arch groined to the main 

 vaults ; the increase of the span of the arches upon the same piers, (for he 

 did not understand Mr. Barry's report to contemplate that) and in widening, 

 winding and dividing the approaches for the double purpose of use and de- 

 light. It was quite clear, however, that as his remarks were written in Sep- 

 tember of last year, and — with the wood. cut illustration of the subject which 

 appears with the text — printed in October, though not published until February 

 of this year, he might claim some credit for having taken the same view of 

 subject that had already, he doubted not, presented itself to the mind of the 

 their eminent contemporary, whilst it might be held to strengthen, in some 

 degree, the view they had both taken, that it had occurred to both Mr. Barry 

 and himself, without communication or knowledge indeed, of each other's 

 doings, to support it by the same train of argument. 



ELECTRIC TELEGRAPH. 



Mr. Wushaw, the secretary, read a paper at the Society of Arts, on Wed- 

 nesday May 17, explaining Messrs. Cooke and Wheatstone's telegraph. 



The practical electric telegraph comprizes two modes of applying elec- 

 tricity to telegraphic purposes : — 1st. The " Galvanometer, which acts by the 

 deflecting power of galvanometer coils on magnetic needles," and 2nd. The 

 " Mechanical form which gives its signals through the agency of the Electro- 

 Magnet on Mechanism." Every instrument yet employed may be classed 

 under one or other of these heads ; and it is only fair to Mr. Cooke to ob- 

 serve, that he had, previous to his acquaintance with Professor Wheatstone, 

 worked out in detail, and made several instruments of both descriptions, 

 and that he has alone thoroughly worked out the entire system on which 

 these instruments are arranged for the purpose of making them act recipro- 

 cally. 



Mr. Cooke, by profession a military man, having served in our Indian 

 armies several years, was in March 1836, engaged at Heidelberg in ana- 

 tomical researches in connexion with the interesting pursuit of modeling his 

 own dissections from nature, for the embellishment of his father's museum, 

 a professor of the Durham University. In this self-taught art he had been 

 engaged several months. An occurrence about this time gave, however, an 

 entirely new direction to his thoughts. Professor Moencke of Heidelberg, 

 had invited Mr. Cooke to witness some experiments with a simple apparatus, 

 intended to illustrate the idea of giving signals by electricity — an idea, by 

 the way, which had at that time been before the scientific world for several 

 years. So powerful was the impression produced on Mr. Cooke's mind by 

 these experiments, and so convinced was be of the possibility of applying 

 electricity to the practical transmission of telegraphic intelligence, that 

 abandoning his other pursuits, he devoted himself from that hour to the 

 present moment exclusively to the practical realization of the electric tele- 

 graph — with what success, let those judge who have seen it working on the 

 Blackwall Railway, for the last three years, or as now extended, and jester- 



