For the best part of sixty years I have been fascinated by philosophy. My bookshelves groan under the weight of publications on the subject, from Ludwig Wittgenstein’s Philosophical Investigations, to Cathcart and Klein’s Plato and a Platypus go into a Bar. Of the former I got lost on page 6—and pages 1-5 were the preface... Plato and a Platypus is quite hilarious, and is an exposition of philosophy through mainly Jewish-American humour. I have read many other similar books, but to date the only knowledge on the subject that I have firmly committed to memory, is Monty Python’s Philosopher’s Song.
I’m now trying—for the umpteenth time—to read Bertrand Russell’s surprisingly accessible History of Western Philosophy. I have reached the point where he is expounding the theory that Plato might well have ‘invented’ Socrates. The argument is that what he (Plato) says about Socrates conflicts with Xenophon’s version of the man. Xenophon, like Plato a pupil of Socrates, was ‘not very liberally endowed with brains’ and ‘conventional in his outlook.’ Russell’s thesis is that the Platonic Socrates—the Socrates described by Plato—was a fascinating and most interesting character, substantially embellished, Russell suspects, by Plato’s considerably literary and intellectual talents and possibly even expressing Plato’s own ideas. It is fascinating stuff but by tomorrow I shall have forgotten it. I am reminded of an incident during my graduate student days. I was most fortunate to have Professor Alan Gibson, FRS, as my supervisor. He was an astonishing man; not only a gifted scientist and educator but also a very able administrator. I struggled during my research project which did not start well when I made it very clear to him that I did not understand Ohms Law... We were at an Opto-Electronic conference in Manchester. Alan was due to present a keynote paper first thing in the morning that followed an evening spent by me carousing in the bar. On going to bed I wondered why my travelling clockwork alarm clock was showing the completely incorrect time. I reset it, adjusting the alarm to wake me up in good time for Alan’s lecture. It did wake me up, but it was only that evening on coming back to the room that I realised that the reason the clock appeared to be wrong was that I had placed it upside down... There must be a wonderful metaphor there, but for the life of me I cannot find it. Anyway, I attended Alan’s talk and it was one of those rare Damascene events. As I listened to him explaining with complete clarity a most abstruse and subtle point, the scales were lifted from my eyes and for a few precious moments I was able to understand something that until then had completely eluded me. I never forgot the incident, that is to say the magical feeling of comprehension; the point itself was lost to me by lunchtime that day. I shall soldier on with Russell. At the very least having forgotten it all from the previous reading, every new idea comes as an exciting revelation.
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In our Time, the regular discussion programme chaired by Melvyn Bragg, is the very best of BBC Radio. Each week three working academics are assembled to discuss a topic chosen from an enormously diverse range of subjects in the arts and sciences. Some weeks are better than others. Sometimes an interesting subject is spoiled by poor communicators; likewise, an apparently dull topic can be made fascinating by gifted and informed academics. Occasionally, and last Thursday (29 February) was an occasionally, a set of great and knowledgeable communicators discuss a really fascinating subject and the programme positively catches fire.
The subject in question was Heisenberg’s Uncertainty Principle. The academics: Fay Dowker from Imperial, Harry Cliff from Cambridge, and Frank Close from Oxford, were at the absolute top of their game. Apart from the thoroughly lucid way each one of them dealt with the subject, they were relaxed, there were a few jokes and some light-hearted banter, and some superb analogies: atomic and molecular spectra were likened to a bar code. Quite brilliant! The Uncertainty Principle states that if you know the position of a particle fairly well, it’s momentum is uncertain. Likewise if you know its position in time accurately, you don’t know its energy. The consequences of this for many aspects of science are huge. I think it was Harry Cliff who cracked the joke: Heisenberg gets stopped for speeding. “Do you know how fast you were going?” Says the officer. “No”, he says, “But I know exactly where I was...” I have listened to the programme twice now—including the extra minutes on iPlayer—and I can say with some confidence that for anyone who is interested in science, cosmology, or even philosophy and religion, this programme is a must. I think it is probably the best In our Time ever. As a ‘Sixties Science Fiction nerd I have been vegging out on classic Isaac Asimov on Audible. They have the original Foundation series, the I Robot stories—so much better than that cretinous Hollywood film abortion—and the Robots and Empire books. They're dated but by jingo Asimov could spin a great tale!
It’s all interspersed with Jeeves and Wooster as narrated by Stephen Fry. All highly amusing and escapist stuff, but these days can anyone suggest anything better? Answers on a postcard please ...
Many people driving under Ironbridge, where the Great Western Railway crosses Uxbridge Road in West London, will be unaware that it consists of three bridges side by side. And since two of them are composed of two spans of a different character, there are actually five bridges there. However Ironbridge is not to be confused with Brunel’s famous Three Bridges (which are actually only two), only a few hundred yards away where a road crosses a canal, which itself crosses over a railway line at the same point.
The illusion (that there is just one bridge there) at Ironbridge can be understood from the attached pictures, courtesy of Google Maps, which show views from either side of the ‘bridge’.
But, I hear you say, if there are five bridges there, where are the other two? To answer that, we must go back 189 years to 1835 when Brunel was planning his Great Western Railway. Immediately after the Wharncliffe Viaduct, that magnificent series of brick arches crossing the valley of the River Brent just after Hanwell Station, Brunel had to bridge what was then the Uxbridge Turnpike. And being Brunel and, in a perversity that he was to repeat more than twenty years later with his Three Bridges, he elected to design a structure to cross the turnpike at the exact point where it was crossed by Windmill Lane (and Windmill Lane is the road at the Three Bridges).
The difficulty of building a bridge across a crossroads was compounded by the fact that the railway crossing was highly skewed; the angle between the main (Uxbridge) road and the line of rails was only 23°—equivalent to a ‘skew angle’ of 67°—meaning that from simple geometry, the length of a single span would have to have been more than twice the combined width of the road and walkways on either side. The Act of Parliament authorising the building of the GWR required a forty foot width of road with two walkways each of ten feet either side. To cross a 60 foot gap at a skew angle of 67° requires a bridge span of more than 150 feet. Because of the highly skewed angle, an arch bridge either in brick, stone, or cast iron would have been impossible. A girder bridge was the only viable option, but in 1835 the only girders available were of cast iron, and they were limited in length to around forty feet. Ever resourceful, Brunel first convinced the Commissioners of Roads to reduce the road width to thirty feet, the walkways to five feet each, and also to allow him to ‘straighten’ the Uxbridge Turnpike so that the skew angle was reduced to 60°. In addition he was permitted to reduce the height of the road somewhat. He then devised an ingenious structure using a number of intermediate columns to support a grid of cast iron girders, none of which was more than 34 feet in length. Two lines of eight columns each were erected on either side of the Uxbridge Turnpike between it and the walkways, and girders were laid longitudinally along their tops, supporting transverse girders over the roads. The gaps were filled in with brick arches. But Isambard was not content just to produce an elegant solution to an awkward engineering problem, he wanted to do so with a flourish and make a statement. It may be that the prospect of his proposed flamboyant design helped to persuade the Road Commissioners to agree to his reduction in the road width and the other concessions, since the bridge would undoubtedly be a notable and interesting landmark on the road. He designed it such that the approaches, when viewed from either direction along the Uxbridge Road, appeared to be symmetric. On the right hand side was the end of the embankment with its brick abutment; on the left was a brick ‘folly’ closely mirroring the masonry on the opposite side. There were also some leading overhead girders between the two, quite superfluous to the bridge structure, which created a sort of ‘proscenium arch’ portico, framing the lines of pillars and girders in a most dramatic way. The effect is strikingly apparent in J C Bourne’s beautiful lithograph of the bridge dating from shortly after its completion in 1839. The skew bridge at Hanwell was quite unique, and demonstrated Brunel’s determination to find original solutions to difficult engineering problems. In the early summer of 1837, after Brunel's skew bridge at Hanwell was complete but before the railway proper was open, one of the main girders failed. The girder weighed 8.5 tons and was supporting a dead weight of 50 tons of bridge, plus the weight of any trains passing over. Fortunately the bridge did not collapse; the grid of girders was fixed together using mortise and tenon joints and these, together with some tie-bars, and the substantial timbers which supported the rails held the bridge deck together. The broken beam was quickly shored up with timber, and the bridge reopened. On 8 June, Brunel wrote to Grissell & Peto, the contractors who had built the bridge, telling them ‘No time must be lost ... to remedy this serious defect’. It was a very serious defect, and there were two possible causes: either the girder was faulty, or it had been incorrectly designed—and the designer was I K Brunel. Subsequent events showed that the casting certainly was faulty; whether the design was also marginal is a moot point.
The Commissioner of Roads, Sir James McAdam, with whom Brunel had probably negotiated the significant concessions on the bridge specifications, had become alarmed by the failure and retained a consultant to investigate. Sir Robert Smirke had extensive experience with cast iron beams, having introduced their use into domestic architecture. His younger brother, Sidney Smirke, took over from him when he retired, and designed the famous circular readers-room at the British Museum. Robert Smirke visited the Hanwell bridge in the company of McAdam, and on 20 November 1837 wrote to the commissioners saying that in his opinion the design of the bridge was perfectly good ‘if sufficient means have been taken to prove the soundness of all the castings’. He had spoken to ‘Mr Brunel’ who told him that before the timber framing supporting the ironwork was removed (having been in place for five months at this point), this would be done. The entire bridge, including the new girder, would be proved by Passing over it carriages loaded with a much greater weight than will ever be required at other times, and as the work is now completed, I do not know how any other or better proof can be obtained. Smirke’s words suggest that he was not entirely happy with the situation. Evidently Brunel managed to satisfy him that the bridge was safe, and the Great Western Railway opened for commercial traffic from Paddington to Maidenhead on Monday 4 June 1838. All was well for nine months, but in 1839, the West Kent Guardian reported that on the morning of 18 March just as a train was passing over the bridge ‘passengers were thrown into the utmost consternation by hearing a report resembling that of a heavy cannon...’ The main girder on the other side had broken in half. This time it was a passenger-carrying train that had been passing over the bridge. A tragedy was averted by the interconnected structure of the bridge and again it did not collapse, but McAdam must have been furious given the previous tests and assurances, and Brunel would have been very seriously concerned. Wasting no time, the company had a gang at the bridge that evening to shore up the broken girder. To compound Brunel’s misery, Daniel Wood, a gravel-digger who appears to have volunteered as a helper to the gang, was killed when a two hundredweight baulk of timber being lifted into place fell ten feet on top of him; the inquest into his death was widely reported in the newspapers. Two days after the incident Brunel wrote to Grissell and Peto: The fracture is ... in the corresponding girder and nearly at the same place as in the former case and apparently from exactly the same cause. I have had a piece drilled off and it consists of a mass of half sand half iron. That casting too had been faulty; eight-and-a-half tons of molten iron contains a considerable amount of heat, and part of the mould, which was made of sand, must have collapsed into the liquid iron under the thermal shock leaving no outward sign. There was a flurry of correspondence. A Mr Bramah, probably the subcontractor to Grissell and Peto who had cast the girder, had written to Brunel expressing doubts regarding its design. Brunel ‘returned’ the letter to Grissell and Peto writing: Had Mr Bramah or you expressed any doubt previous to the commencement of the work and had you declined being responsible it might be right for you to repeat the grounds of your fears—but the result of the accidents that have happened have proved that there is no cause for alarm. That the unsound girder should have stood what it has done is the strongest proof possible that a sound one of the same dimensions would safely stand anything that comes upon it. Here is Isambard keeping his head, making a very good point regarding the design, and clarifying contractual (and moral) responsibilities should it come to an argument as to ‘who pays’. He, of course, had far more to lose than the cost of replacing a girder. The bridge failure was public knowledge, and it was vitally important to establish that although the casting was faulty, the design was not. A new girder was duly cast and proved at a different foundry, and evidently transported to Hanwell with great despatch. Thus on 18 September Brunel wrote to Sir James McAdam: It was quite accidental that the [new] girder was proved and carried down to Hanwell without informing you. The obtaining the casting had occupied so much time that everybody was anxious to lose no more ... the casting has all the appearance of being an excellent one, it has been carefully proved, we have no means of proving it at Hanwell and if this be required it must be transported [back] to Limehouse. But I can furnish you with certificates of the proof to which it was subjected, signed by highly responsible parties, the contractors Grissell & Peto, the foundry, Messrs Seawards and my assistant and this I trust you will consider sufficient as proving the fact Reading between the lines, it is clear that Sir James had wanted an independent inspection of the proving process before the new girder was committed to the bridge. McAdam decided to get his consultant to press Brunel on the matter, and Smirke demanded further proof of the soundness of the bridge. On 4 November Brunel wrote to him: The new girder has been fitted into its place at the Metropolitan Road bridge at Hanwell and is now ready for fixing. In consequence of your letter of 4th Ult I have considered what method could be devised for increasing the security of the work and propose for that purpose to lessen the weight to which the girder is subjected very considerably and to prevent any vibration from the passing of the trains being communicated to the cast iron by the following arrangement. 1st To remove the brick parapet walls which now rest on the main girder and which together weigh about 30 tons and to substitute cast iron plates weighing only about 6.5 tons and of sufficient strength to carry themselves as well as hold up the girder in the event of its breaking. 2nd To remove the small brick arches now forming the floor of the bridge and which with the concrete constitutes a load of about 70 tons now resting on the two main girders and to substitute a timber flooring weighing only 16 tons and upon which the rail timbers would be laid so that any vibration upon the rails could not be transmitted to the girders. The total reduction in dead weight will then be 78 tons 10 cwt or 39 tons 5 cwt upon each of the main girders having consequently a very great deal of excess strength while at the same time from the introduction of the timber and the cast iron parapet the girders will be exposed to less injury and would be supported in case of failure of such could then be considered possible. I trust you will approve of these proposals and that you will have the goodness to communicate such approval to Sir James Mc Adam as early as possible. I am under promise to him not to proceed with the fixing of the girder. The brick arches and their cement infill contributed 70 tons of deadweight to the two main bridge girders. In his letter to the contractors Brunel said that the new girder (the second replacement) had been proved to ‘78 tons, 11 tons more than his maximum.’ Thus the maximum design load per girder was 67 tons. The function of the brick arches was to provide a flat and continuous bridge deck for the rails as well as a walkway for maintenance staff; was it really good design practice for this relatively minor feature of the bridge to consume almost half of its load-carrying capacity? Furthermore when pressed, Brunel cheerfully replaced it with wood saving a weight of 54 tons! Likewise, a straightforward alteration to the parapets saved more than 20 tons. In his letter to Smirke of 4 November, Brunel had said that the new girder ‘has been fitted into place ... and is ready for fixing’. Exactly what this meant was clarified by a letter to Sir James McAdam dated 21 November, and judging by Brunel’s words, Sir James was far from happy. Brunel began his letter: My Dear Sir James, I have received yours of the 18th. I am sorry it does not show that courtesy and confidence which you have uniformly displayed towards me in former correspondence and which I feel I deserve at your hands. I regret that before assuming that I was about to do something ‘in violation’ of any understanding or request, you had not applied to me to ascertain if such were the case as you would at once have been satisfied that it was not so. There is more to be done to the girder before fixing than can now be completed by Sir R Smirke’s return; it has to be raised to its [final position] and marked then lowered or removed to be chipped and filed before it is ready to be fixed and this alone I am about to proceed with. That no further delay that can possibly be avoided shall take place when it is definitely determined what is to be done with it up to the present time the girder remains in the lane close by. This is not quite what he had said to Smirke nearly three weeks earlier. Then he said that the girder had been ‘fitted into its place’; now he appeared to be saying that that still needed to be done. He went on: I should add that your surveyor has informed my assistant that they shall not move the girder from where it is, that he should prevent it by constables. That is going rather far and not only threatening that which he has no authority to enforce but adopting a course which if he had the authority is totally uncalled for. It seems that there had been an unpleasant confrontation at Hanwell, and it is not difficult to deduce what had happened. A few days after the failure of the first girder Smirke and McAdam had inspected the bridge, and either by then or shortly afterwards, the faulty girder had been replaced before either of them could witness the proving. Subsequently Smirke had had a meeting with Brunel and was presented with a fait accompli in that only by accepting Brunel’s proposed method—using heavily loaded waggons—could the girder, by default, be proven to be good. McAdam was obviously suspicious that Brunel once again was trying to out-manoeuvre him. Brunel continued: You have requested that the girder shall not be fixed until Sir Robert Smirke is satisfied of its soundness or shall have arranged with me on the subject. I have no intention of neglecting that request but waiting Sir R Smirke’s return I am going on with all the preparation required and I informed Mr Brouse [McAdam’s surveyor?] that such was my intention He finished by appearing to invite Sir James to withdraw his letter, otherwise Brunel would have to make a formal response ‘entered upon the official correspondence of the office’—was this letter then not a formal response? Evidently ruffled feathers on both sides were eventually smoothed over, the new girder was fitted, the brick arches removed, the other alterations made, and the bridge was opened for business. But the law of unexpected consequences reigned supreme; in substantially lightening the bridge, Brunel had opened it up to a new and fairly obvious danger that was eventually to spell disaster, and not just at Hanwell. By 1847 the Great Western Railway had connected London to Exeter via Bristol, and the South Devon Railway was being built to extend the line to Plymouth. But on 22 May 1847, the Bucks Herald ran the following story, repeated in many other newspapers:
The railway bridge of the Great Western Railway over the turnpike road at Hanwell took fire on Thursday [20 May] at about 12 o’clock, and has become impassable. The scene was and is indescribable... Although there was talk of ‘vile incendiaries’, it seems that a piece of lighted coal probably fell from an engine and set the timber bridge deck alight. The railway line and Uxbridge Turnpike were completely blocked. Trains had to stop either side of the bridge and passenger[s] are obliged to alight, and walk, slide, or tumble down the embankment and scramble up again how they can. Considering the height and steepness of the embankment, it must have been a major trauma for the passengers. At least eight of the cast iron girders had cracked from differential heating. Once more the bridge was shored up with timber and within a day or so, it was open for normal traffic. Brunel must have been beside himself. In using wood to reduce dead weight, he had opened the bridge up to the ever-present danger of fire. And there was a further tragic consequence. The accident had been extensively reported in the national press, and it is possible that Brunel wrote to his friend Robert Stephenson to share his woes over cast iron girders. Stephenson’s own cast iron girder railway bridge over the River Dee had been open for nine months. The span length of his bridge was 100 feet, and he had achieved this by using three girders bolted end to end and strung with wrought-iron bars to provide extra tensile strength to the bottom flanges. On the evening of 24 May 1847, four days after the fire at Hanwell, the bridge failed as it was being crossed by a train. The engine and tender managed to get across but five carriages ended up in the river and the fireman and four passengers were killed. An excerpt from the subsequent accident report: On the day of the accident, six trains had passed without any symptom of danger. On the afternoon of that day, immediately before the fatal train passed, about 18 tons of broken stone had been laid upon the planking as a protection against fire from the cinders of the engines, one of the bridges upon the Great Western Railway having been burnt about the same time through this cause. The report went on to say that even with this extra eighteen tons, the load on the bridge would not have exceeded what it had previously withstood from trains, and the actual cause of the accident was likely to have been that the wrought iron tie rods had been incorrectly fitted. Nevertheless, the gravel laid as a fire retardant seems to have triggered the collapse. Both Stephenson and Brunel must have reflected with not a little discomfort on the risks of using cast iron girders. A few months after the Dee Bridge accident, in August 1847, I K Brunel was called as a witness to the resulting public enquiry appointed ‘...to inquire into the Application of [cast] Iron to Railway Structures.’ Even before the enquiry started Brunel had written to the commissioners on the question of cast iron beams refusing to condemn their use. He wrote: Who will venture to say ... that means may not be found of ensuring sound castings of any form ... and of a perfectly homogeneous mixture of the best metal? As a witness he was asked point blank to condemn trussed cast iron beams [as used on the failed Dee Bridge]; he replied: By no means. But I should observe generally in answer to this question, that I avoid the use of cast iron whenever I can ... Although Brunel and Stephenson were professional rivals, they were personal friends, and Brunel’s staunch defence of cast iron girders has been frequently ascribed to his personal loyalty to Robert Stephenson. The writer P S A Berridge comments: ...it was touch and go whether a charge of manslaughter would not be brought against Robert Stephenson. However the multiple failures at Hanwell point to more than a little element of self-preservation. Had Brunel condemned the use of cast iron, the roads' commissioner, Sir Robert McAdam, might well have insisted on a complete rebuild of the Hanwell Bridge; he could even have demanded that it be closed to rail traffic until that had been done. The potential financial and reputational damage to the GWR—and Brunel—could have been considerable. Brunel’s skew bridge at Hanwell had now ‘failed’ three times. The fire was clearly accidental but it could be argued that the extensive use of wood in an environment where the spillage of burning coals from steam locomotives was an ever present danger, was poor design practice and just asking for trouble. McAdam’s views have not been recorded, but there is indirect and circumstantial evidence to suggest that the bridge was securely shored up with timber for some considerable time. Nine months after the fire at an unrelated inquest into the deaths of two people from falling brickwork at Euston Station, counsel was making the point that there was no limit to the time that support scaffolding could be left in place if it was needed. His comments were reported in The Times: There was an iron bridge at Southall, on the Great Western Railway, from which the scaffolding, although it had been erected many years, had not yet been removed. Much public inconvenience had arisen in consequence of there being danger of some accident in passing under the bridge... The Morning Post version was slightly different: The Great Western Railway Company ... had kept up the scaffold under an iron bridge erected near Hanwell for the last five years in consequence of some slight doubt as to its stability, and this in spite of great public inconvenience. The barrister whose speech was being reported may have been indulging in some studied hyperbole, since it was at most nine months since the fire, but ‘many years’ or ‘five years’ is considerably longer than nine months. It is not impossible that either the Road Commissioners, or Brunel, or both, had decided to leave the timber framing in place under the bridge as a precaution following the second girder failure in 1839. Perhaps Brunel was repeating the ruse that was taking place at about the same time at his brick arch bridge at Maidenhead. Critics said it was too long and shallow and would fall down as soon as the centring (wooden support) was removed, and indeed some courses of bricks did become detached when this was done. The contractor conceded that he had allowed insufficient time for the mortar to harden and effected a repair. Brunel decided to have some fun at his critics’ expense, and instructed that the centring be left in place but eased so that it was not actually supporting the bridge, while appearing to do so. His stratagem was revealed many months later when the centring blew down in a winter gale leaving the bridge perfectly sound. Meanwhile, the Hanwell Bridge needed to be rebuilt and from Brunel’s point of view he probably determined never again to use cast iron girders. The fire had spotlighted yet another disadvantage of cast iron; the report of the Railway Commissioners into the accident observes: It would appear that, from the burning of the floor, the undersides of the girder would not be exposed to any great heat, while the upper parts were enveloped in flame, and that the unequal expansion has broken them on the underside first. Cast iron is brittle and thus quite susceptible to damage from differential heating in the event of being involved in a fire. Of exactly what was done and when following the devastating fire that cracked eight of the cast iron beams supporting the Hanwell Bridge, the public record is frustratingly incomplete. The 1870 biography of Isambard by his son says: ‘... he repaired the Hanwell Bridge with wrought iron’, and the contract for the 1906 replacement of the bridge credits the contractor with £100 for 100 tons of wrought and cast iron (the cast iron was from three of the columns that had been removed). It is an article in the Great Western Railway Magazine on the occasion of the final replacement of the rebuilt bridge that tells us most of what we know: When the railway was opened in 1838 the lines were carried by a cast iron bridge with timber decking; this was destroyed by fire in 1847, and from that year dates the bridge now to be removed. It was designed by Brunel, and consists of wrought iron box girders supported on brick abutments and cast iron columns. In the ten years since Brunel had designed the original Hanwell bridge, knowledge of the use of wrought iron in the construction of girder bridges had grown exponentially, as had the availability of that material. Brunel himself was finalizing the design of a railway bridge at Windsor in wrought iron. It was a 200 foot span bowstring arch of the type that he would probably have used at Hanwell had the technology been available then. Robert Stephenson had already started construction of a stupendous wrought iron tubular girder bridge using several 400 foot spans to cross the Menai Straits. Stephenson had tasked William Fairbairn with testing different riveted wrought-iron structures with a view to finding the optimum design for a girder made of that material. Wrought iron was more expensive than cast iron since it had to be worked in molten form to remove excess carbon and other impurities, and then hammered or forged into bars or plates. To manufacture girders, parts had to be cut, bent, drilled, and riveted together. The problem of invisible air bubbles or other casting faults was effectively eliminated; wrought iron could be forged into thin plates and readily bent, and its resistance to tensile forces was three times greater than cast iron. Furthermore, unlike cast iron which tended to break without warning under excessive loads, wrought iron structures would bend beyond the elastic limit or crumple relatively slowly. It was therefore intrinsically a much more versatile and safer material to use for bridges. The conventional form of a girder was an I-beam, with a top and bottom flange connected by a vertical part called the web. The cast iron girders used by Brunel in the Hanwell Bridge had been of this form. The depth of the main girders—the ones that initially failed—was two foot two inches, the flanges were eleven inches wide, the thickness of the flanges and web was four and a half inches, and the length was thirty-four feet. As noted earlier, the weight of each was just under eight-and-a-half tons, and they had been ‘proved’—supported at their ends and loaded with test weights—to seventy-eight tons. An I-beam under load experiences compression, or a ‘crushing’ force, in the top flange, while the bottom flange comes under tension. Cast iron is immensely strong under compression, but five or six times weaker in tension, and it was this weakness under tension that necessitated the beams to be so massive in order to provide sufficient cross-sectional area in the bottom flange to withstand the design load. Fairbairn’s findings with wrought iron were that a rectangular ‘tube’ or box was the best configuration, improved considerably by a cellular top which provided the optimum resistance against crushing forces, and this was the design adopted by Stephenson for his Menai Straits bridge. And notwithstanding the greater intrinsic cost of wrought iron and the extra work needed, Fairbairn showed that a riveted wrought iron I-beam was virtually the same overall cost—while using just 40% of the iron—as a cast iron beam capable of bearing the same load. The Hanwell Bridge could have been entirely and securely reconstructed using a wrought iron bowstring girder like the Windsor design. But cost was clearly a factor as Brunel himself was later to remark—see below—and much of the existing structure was undamaged and could be reused. There was also the question of the effect of a lengthy disruption to railway services. It was decided to rebuild the bridge using wrought iron box girders supported on the existing pillars and abutments. The photograph accompanying the 1906 article on the bridge reconstruction taken shortly before it was demolished shows that, by comparison with the J C Bourne lithograph of the original bridge, the appearance was largely unchanged. All that is known about the actual construction seems to be contained in an incomplete set of just three rather poor drawings that have survived in Network Rail archives. There is a plan of the entire bridge which confirms that the general layout was the same as before, with longitudinal girders over the tops of the pillars, and transverse girders across the road. The number of load-bearing transverse girders had been reduced from thirteen to eight, and there are at least three different box girder designs, each one a depth of around two foot three inches, about the same depth as the cast iron girders they replaced. Widths varied between two and three feet, with numbers of cells—depth six inches—between four and zero. Tantalisingly, the nature of the bridge deck is quite unclear. There would have to have been substantial support for the rail timbers over the gaps between girders some of which were twelve feet apart. The plan appears to show a ‘cattle grid’ of further box girders between each transverse beam. Reference to another drawing identifies these as ‘Imitation girders’ consisting of a shallow box section top, two feet wide by around six inches deep—with a very thin-wall box-obviously not designed for load-bearing—below. A much later note on the plan states: ‘Weight of floor 26 lbs per square foot’ which is consistent with the entire deck being composed of shallow box section.
The plan also shows that all of the girders—longitudinal, transverse, and diagonal—were riveted together making an immensely strong integrated unit. They were designed with economy and elegance showing that Fairbairn’s experimental results had been fully absorbed and acted on. (Had Stephenson made Fairbairn's results available to his friend?) Construction must have presented some interesting problems, since most joints were riveted, and the top cells were only eight inches wide by six deep. To close a rivet it is necessary to access both sides—one for hammering, the other for the tool which holds the rivet in the hole as it is hammered from the other side, although hydraulic riveting machines were just starting to be used at the time. The plans do show that some joints, ‘Lap joint for last side plates’, were closed with nuts and bolts. Whatever the actual constructional details were, the process of rebuilding the bridge must have been a logistical nightmare. The new girders were the same depth as the ones they replaced but the fixings were entirely different and definitely not compatible. The bridge was also badly damaged from the fire and supported by timber framing. Could the work have been done piecemeal without closing the entire bridge? Closure even for a short period would have inflicted severe damage on the reputation and revenue of the company. The new girders did have one very considerable extra advantage over the cast iron girders they replaced: since they were riveted together from a number of small parts, they could be built up bit by bit in situ. Removing the old girders would be problematic, but it is possible to envisage a procedure whereby the bridge deck was wedged up an inch or so on timber supports. The cast iron girders could then be removed piecemeal and the box girders installed. Raising the bridge deck even by an inch would destroy Brunel’s ‘billiard table’ and a severe speed limit would have to be enforced, but this would be far better than closing the bridge completely. Furthermore something of the sort must have been done following the 1839 girder failure in order to replace the broken beam with its multiple fixings to the transverse girders. Much of the foregoing is speculation in the absence of any evidence to the contrary. The complete closure of the bridge for several months or even weeks and the corresponding disruption to road and rail traffic would surely have been noted in the newspapers, both local and national, and no such stories exist. Along with the uncertainty in the exact design used and method of construction, there is very little to confirm exactly when the bridge was rebuilt. There is a clue in a letter Brunel wrote to one of the GWR directors on the question of cast iron girders. On April 18 1849, he wrote: ... our Great Western road bridge at Hanwell, which, since 1838, has always been under repair, [and] has cost its first cost three times over ... I never use cast iron if I can help it; but in some cases it is necessary ... The tendered cost from Grissell and Peto for building the original Hanwell bridge had been £6750. There were the costs of replacing the two failed girders—the responsibility of the contractors—but the majority of the extra £13,500 must have been accrued by the wrought iron rebuild. It is likely, therefore, that it was either complete or well underway by the date of Brunel’s letter. Around 1876 the decision was made to double the number of lines on the GWR starting at the London end. Herapath’s Railway Journal reported that the two new tracks added to the north of the existing railway would be used for ‘auxiliary or slow goods lines ...’ Fast passenger trains would continue to use the original lines. At Hanwell this involved widening the embankments, the Wharncliffe Viaduct, and the skew bridge. Work on the Wharncliffe Viaduct was extensive but relatively straightforward. The Uxbridge Road crossing presented a major difficulty. Brunel had been in his grave for more than fifteen years, but the legacy of his problematic bridge continued to haunt the Great Western Railway Company. The issue was that the support columns and girders on the north-west side of the original bridge (the Southall side), as well as the flamboyant ‘proscenium arch’ and its folly, were strung out immediately under where the new lines would be positioned. Any new span would have to be built over the top without interfering with the function of the earlier (1847) structure. A further complication arose from the fact that the layout of the crossroads had to be preserved. The new bridge, being parallel to the existing one, would have to be located a significant distance north-west of the point where the two roads crossed. Either a very long span or two separate bridges, one over each road, would be needed. No contemporary documentation regarding the bridge can be found. As with Brunel’s box girder bridge, most of what is known is from the 1906 article in the GWR magazine written some thirty years after the event. It says: In 1876-77 the northern [north-westerly] wing of the original bridge was demolished to admit of a widening for additional lines, the structure being formed of wrought iron lattice girders, cross girders and an iron plate floor. The decision was made to build two spans utilizing one of the existing cast iron pillars and a new brick ‘island’ structure for the central support, and extended brick abutments to the widened embankments at either end. A lattice girder bridge design in wrought iron was chosen for the main span crossing the Uxbridge road. William Fairbairn’s experiments had shown that the box girder was the most efficient use of material in achieving the maximum load bearing capacity for a given amount of wrought iron used. The lattice girder ‘through truss’ retained most of the benefits of a box girder while being more versatile, more economical of material, easier to fabricate, and much easier to maintain corrosion free. The truss consisted of two substantial I-beams connected between their bottom flanges with transverse girders to form the bridge deck; their webs were not solid as in conventional I-beams, but double layer wrought iron trellises. This design was very popular at the time and many examples can be seen on the British railway system, including the bridge carrying the railway across the River Thames at Kew. The second, much shorter span bridged Windmill Lane, and consisted of a pair of conventional I-beams with solid webs. It is evident that the deck plan of any skew bridge built with economy is a parallelogram rather than a rectangle. In order that the main girders are no longer than they need to be, they are offset with respect to each other along the longitudinal axis of the bridge. The deck plan of each span of the new bridge was a trapezium, and in each case the two girders were longitudinally offset—but in different directions—and in both cases one girder was longer than the other. It is difficult to visualise the layout without pictorial assistance but a full plan showing both Brunel’s bridge with all of its columns and girders and the two new structures would be more confusing than helpful. There is a large-scale map in the National Archives dating from 1913 which shows just the road layout and the outline of the bridges, and this has been annotated to show the position of the two new bridges. In order to accommodate the new span, it was necessary to demolish the proscenium arch and folly on the west side of Brunel’s bridge, and remove any embellishments on top of the girders there. The clearance between the bottom of the new bridge and the tops of the box girder array on the existing bridge was chosen to be around fifteen inches; a box shaped spacer of this depth was fixed to the top of the existing box girder immediately over the cast iron column at the north-west corner of the crossroads. This also supported one side of the short bridge crossing Windmill Lane. It is presumed that main line trains continued to use the original bridge during these works, and that a timber support structure was built over the two roads to allow unrestricted road traffic to continue while the new bridges were built. The photograph, which was taken last year, shows about the best view possible of the trellis bridge given that it is sandwiched between the two later steel structures. The picture also affords a nice view of the shorter span built to cross Windmill Lane. The unsightly blue boarding on the right blocks in an old builder’s yard which was built on the original position of Windmill Lane before it was diverted sometime after 1913 to its present position. The bridge deck is continuous from the trellis bridge, over the brick island, and the short bridge over Windmill Lane The new spans were finished by some time in 1877 and the trellis bridge would have completely changed the appearance of the Hanwell bridge to anyone coming along the Uxbridge Road from Southall, likewise to a traveller along Windmill Lane from Greenford. From the Hanwell side, the bridge was unaltered, the new span being entirely hidden from view by Brunel’s theatrical arch and its accoutrements which remained on that side of the bridge. So it is most curious that nothing about this substantial change in a local landmark can be found in any of the local newspapers of the period. Likewise no photographs are to be found in the public domain.
Following the 1877 widening, no further changes were made to the Hanwell skew bridge for around twenty-five years. There is a surviving plan of the 1847 rebuild in the Network Rail archive which is covered in stress and weight calculations in red ink, dated April 1896. This suggests a careful review of the weight-bearing abilities of the bridge carried out in that year. As the technology of steam power had developed from the early days of the railways, locomotives had become steadily more powerful, faster, and inevitably heavier. The 2-2-2 Firefly class from the 1840s weighed 24 tons; from around 1847 there were a number of locomotives of the 4-2-2 Iron Duke class weighing 41 tons. By 1906, the 4-6-0 4000 Star Class locomotive plus tender weighed 116 tons fully loaded with coal and water. The steady increase in the weight of locomotives through the second half of the nineteenth century would have prompted the reassessment of the strengths of many of the bridges on the network including the one at Hanwell. Nothing was done for a few years, but in March 1903 the GWR contracted with Head, Wrightson and Co of Stockton on Tees for the ‘Supply and Erection of Steelwork for Bridges at Hanwell’. ‘Bridges’, because there were three of them, including a steel truss to replace Brunel’s box girder bridge of 1847 and a new single line goods crossing. It seems that the railway company was determined at all costs to preserve four operating tracks, two main line, and two ‘relief’ or goods lines, during the reconstruction work. When the crossing was doubled in width from two to four tracks in 1876, a small extra island of embankment—mainly brick—was erected at the north-west corner of the crossroads and this, together with one cast iron column, acted as the central support for the two spans of the new bridge. Now, this island was to be extended to the north and west, the embankments and their abutments adjacent to the existing bridge were widened, and a single line of rail was to be supported on yet two more spans. This was the ‘1903 ... third widening ... to accommodate a goods relief line’ which had been mentioned in the 1906 article in the GWR magazine. From the contract: The new single line bridges over Greenford Lane [Windmill Lane north of the bridge, renamed] and Uxbridge Road forming the widening must first be erected; after both are completed the Company [GWR] will lay their permanent way and commence running traffic over the widening. The reason why this extra line was needed is unclear and was not clarified in the contract. The Wharncliffe Viaduct was not widened, so the fifth line could extend only for a few hundred yards towards the east where it stopped just before the viaduct, although points connected it to the adjacent ‘up’ goods line. To the west, the line proceeded towards Southall where it become lost in a tangle of sidings. So what was its purpose? It could not increase the overall railway capacity because that was limited to the four line width of the Wharncliffe Viaduct. Was it built for heavy goods traffic deemed too near the design limit for the latticework wrought iron bridge, or was it just insurance in case the main line (Brunel) bridge rebuild ran into technical difficulties or took too long? The likely reason for the extra span and the complex and piecemeal way of building the main span (see below), was that the company wanted to keep as many lines as possible open at all times over the Hanwell bridge in order to avoid undue disruption to the railway timetable. At the turn of the century the Great Western Railway was the largest railway company in the country with over 2,500 miles of track. Paddington was the London terminus and trains from Paddington had to traverse the Hanwell bridge. Any restriction at the crossing would severely affect both passenger and goods traffic. With the completion of the new single track bridge, there would be five lines crossing Uxbridge Road. One of the main line tracks would be occupied by the building of the new bridge as detailed below, and the adjacent ‘relief’ or goods line would be in fairly regular use ferrying steel parts for the bridge. This would work well for the north-west side on the ‘up’ main line, but for the other side, the side nearest Hanwell, the adjacent line was the up main line. The contract did allow in exceptional circumstances for the main line to be used to transport parts, at which point all passenger and goods traffic would have to use the relief lines and new single line. The new single line consisted of two spans. Crossing Windmill Lane—now named ‘Greenford Road’ or ‘Lane’ on that side—was a short bridge using riveted steel I-beams. The main span crossing the Uxbridge Road was an open structure of the type known as a ‘Pratt Truss’. A drawing from the contract plans shows an orthographic view of the two spans as seen from the north. The Greenford Hotel—now McDonald’s—and trees on the embankment now mask views of the shorter bridge. (There is a rumour, possibly an urban myth, concerning the Greenford Hotel which was one of two hotels built in the area in 1920s/30s. The Greenford Hotel was by the Hanwell bridge on Greenford Road (but some distance from Greenford). A second hotel was built just under two miles further north on the junction between Greenford Road and the Western Avenue in Greenford. The second hotel, a long way from any bridge, was called ‘The Bridge Hotel’. The story goes that the same entrepreneur built both hotels, but someone on their staff confused the two—they were both on Greenford Road—and managed to switch the names. When the mistake was discovered it was too late to rectify it.) A local newspaper story on 27 June 1903 about the flooding of the River Brent mentioned the ‘stream little short of a torrent’ in proximity to the ‘new railway bridge’. This suggests that by that date, three months after the start of the contract, the work on new single track bridge was either complete or substantially so, and this is consistent with the GWR magazine article. (It must have been a prodigious flood considering the elevation of the bridge.) After this for some reason the contract did not proceed as originally written; the final replacement of Brunel’s wrought iron structure did not happen for another three years. The original work-package started in March 1903 with a ten month completion period, so something substantial must have happened to delay the process. The formal go-ahead to Head and Wrightson to commence the work was dated 12 March 1903 and this was acknowledged two days later. The tender was for the sum of £6,482 12s, to be completed within ten months from ‘the date of the order to commence’. A bond of £1,200 provided by ‘two good and satisfactory Sureties’ ensured the ‘due fulfilment of the contract’. A default penalty of more than 18% of the contract value is not surprising given the cost to the railway company of their bridge being partially unavailable for longer than planned. The contractor had to pay the company £50 for every week that the work overran the contracted completion time. It is difficult to see how technical or engineering problems could have delayed the work for so long, and if there were any contractual issues they were settled out of court. The most likely reason for the delay was for ‘convenience’ on the part of the GWR. Perusal of Volume 2 of E T MacDermot’s History of the Great Western Railway does offer some clues. It seems that at the turn of the century some of the inhabitants of Bristol were dissatisfied with the existing railway service and became interested in constructing a rival railway. A Bill came before Parliament in May 1903. It may be that the prospect of competition spooked the GWR board into beefing up their existing timetable, and the last thing they needed would be to have all passenger trains having to slow to walking pace a few miles from Paddington in order to cross a bridge under reconstruction. In the event Parliament threw out the Bill for the new railway in June, due in some measure to the fact that the ‘alleged enthusiasm of Bristol ... has not been crystallised into cash support’. The GWR board must have breathed a collective sigh of relief, but it was no time for complacency. In June 1904, with perhaps an implied ‘nose-thumbing’ at Bristol, the company initiated an ‘express in each direction between London and Plymouth without a stop’. The 246 miles were covered in four hours twenty-five minutes, this being the longest non-stop service in the world. Was it the search for that record that delayed the bridge rebuilding? Two years later, the main contract work finally commenced. It consisted of the replacement of Brunel’s 1847 bridge, with a single steel gantry also to the design of a Pratt Truss. What is curious about this part of the contract is that the fabrication method laid down for the new span seems to be unnecessarily complex and longwinded, and quite likely to lead to error and the need for rework and delay. Reduced to its essentials, one half of the bridge, starting with the ‘up’ line, was to be made available to the contractor. The company (GWR) would remove the rails, ballast, and asphalt, and the contractor, having built a fence between the up and down lines, would proceed to build just half of the bridge on that side resting on Brunel’s bridge, with the two ends of the main girder sitting on temporary elevated supports. While this was going on, trains would continue to use the down line, rumbling past on the other side of the fence. When complete, the company would lay rails over the new half of the bridge and run trains over it. Now the down line would have its rails etc. removed, and the contractor would construct the other half of the new bridge. When this was finished the company would relinquish the up line, the two halves of the bridge would be united, Brunel’s bridge would finally be demolished, and the new bridge would be lowered hydraulically, two inches at a time, to its final position. The plan makes it clear that the rails on the relief, or goods line—the 1867 trellis bridge—were higher than the main line; this was because the bridge had to clear Brunel's 1847 bridge girders. The added gradient was less of a problem for the slower goods trains, and in any case the locomotives were far more powerful by 1867 than in the early days of the railway. One further difficulty was pointed out to the contractor: Attention is called ... to the Electric Tramway with overhead conductor crossed by and adjacent to the works ... So the contractor had to build one half of the bridge, including a forty-five ton, fifteen foot high girder, in an area just half of the width of the bridge with trains thundering past on the other side of a wooden fence. Furthermore, any false move during the demolition of the (metal) Brunel bridge or the lowering of the new steel span, would bring the workmen in contact with several hundred volts and shut down the London United Tramways—and possibly the workmen also ... On 14 April 1906, shortly after the two halves of the bridge had been united, and as the old Brunel structure was finally being demolished, the work was photographed from the ground and the railway tracks. The photograph from the ground is taken from Windmill Lane looking north under the bridge towards Greenford. The new steel truss is virtually finished with the end supported on what appears to be a stack of temporary spacers over the cast iron rocker bearing (top left). Much of Brunel’s 1847 bridge can still be seen, including the remaining folly on the extreme right. Above the column immediately to the right of the horse and cart there appears to be evidence of corrosion on the girder. The electric tram ran along the Uxbridge Road under the bridge from 1901 and two of the standards or poles supporting the overhead wires can be seen just to the left of the horse and cart; it is just possible to see the wires themselves under the bridge. Ten years later, a view of the completed bridge from approximately the same viewpoint, complete with tram. Called in the text 'A Little Known Brunel Masterpiece", this view confirms that as late as 1916, the Windmill Lane part of the bridge was still open. By comparing the tops of the telegraph pole and tram power standard with the bridge deck, it can be seen that the bridge is lower than in the earlier photograph. It was lowered hydraulically by around two feet after the Brunel bridge was finally demolished. The view from the bridge, looking towards Hanwell and Paddington, shows the end of the other girder supported on spacers. This photograph is notable also for showing part of the 1876 wrought iron trellis bridge; the trellis bridge girders are much shallower than those of the steel bridges demonstrating why it is virtually impossible to see it except from directly underneath. The local press had ignored the 1876 rebuild even though it had entirely changed the view of the bridge from the Uxbridge side. It did so again in 1903 when that view changed again with the building of the single line bridge. From that time the trellis bridge virtually disappeared from view, sandwiched between the two outer spans. Again in 1906, with the final removal of Brunel’s bridge, the local press ignored the event despite the fact that, once more, the view was completely changed. The alteration did not, however, go entirely unnoticed. One rather unlikely group of enthusiasts went to press with a story and photograph commemorating the event. The July 1906 edition of Cycling, published a photograph taken from Uxbridge Road on the Hanwell side, together with a half-page story. The correspondent signed himself ‘R. W.’, and wrote: There has passed away during the last few weeks a very interesting structure and notable feature of the Oxford Road. Most London riders will be familiar with the spot beyond Hanwell where the Great Western Railway goes over the cross roads, and will probably recall the peculiar bridge with its 16 piers and maze of cross girders which made the corners so awkward to negotiate ... It is evident from the partially dismantled state of Brunel’s bridge, that the photograph was taken around the same time as the two views reproduced above. Tantalizingly, the large notice on Brunel’s folly is unreadable. It would be fascinating to be able to read what it said... The Hanwell skew bridge complex was now complete and in the form we see today; the layout is shown in the annotated map: The next photograph shows the bridge in its final iteration from the Hanwell side, with trams, circa 1912. The history of Isambard Kingdom Brunel’s skew bridge at Hanwell, its modifications, and its neighbours and successors is all still there in plain sight for anyone who is interested to look, as the last picture amply demonstrates. Peter Maggs
February 2024 Acknowledgements The paper by Brindle and Tucker, I K Brunel’s First Cast Iron Bridges and the Uxbridge Road Fiasco, Trans. Newcomen Soc., 78 (2008) 25-45, is a highly detailed and informative piece of work with a comprehensive set of references without which the present work would not have been possible. John Page, Records Controller at the Network Rail National Records Group, has provided some wonderful high-resolution scans of drawings of the various iterations of the Hanwell Bridge; those used are with the Kind Permission of Network Rail. The two photographs of the bridge taken on 14 April 1906 are © Historic England. The picture of the completed bridge, circa 1912, is from Ealing Public Library. Thanks are also due to Carole Boniface for trawling Ealing Library for suitable photographs, and for material assistance in measuring up the one remaining octagonal cast iron column at the bridge. Despite the depressing and relentless litany of obituaries of my contemporaries—this week Ian Lavender (‘Private Pike’), younger than me—I am still here, moderately invigorated by seven days in a nice hotel in Lanzarote. Sunshine, daytime temperatures between 22°C and 24°C, and far too much to eat and drink... What’s not to like?
I note while updating this website that I published nothing in 2023. I have not, however, been inactive. For several years now I have been working on and off on my memoirs, very brief snippets from which have appeared from time to time in this blog. Short biographies of my mother and father are also being worked on. What has occupied my fairly constant attention for the last six months has been an in-depth investigation into the ‘Iron Bridge’ at Hanwell in West London. This austere structure, which carries the Great Western Railway across the Uxbridge Road, is a landmark I grew up with. The current steel girder bridge is in the form of a ‘Pratt Truss’ (yes really—“Pop Con” movement, please note...), but it started life as one of I K Brunel’s most curious, imaginative, and troubled creations. I will reveal some of my findings in the coming posts. |
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March 2024
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