THE REASON WHY
In their two reports, the members of the Court of Inquiry had addressed two separate but related issues – what had caused the bridge to fall; and who was to blame? On the first point, the report signed by the two engineers, Barlow and Yolland, had been clear and unequivocal – that the cross-bracing on the cast-iron columns had been insufficiently strong to withstand the force of the gale. This was in the first instance a fault of design, though possibly exacerbated by failures of management and workmanship. In Rothery’s view, as we have seen, these failures pointed the finger of blame principally at Bouch, both as the designer and as the overall supervisor of the project.
Yet not all contemporaries, nor all subsequent commentators, have agreed with these conclusions. Over the years there has developed a lively debate both on the causes of the bridge’s failure, and on the attribution of blame or moral responsibility for that event. These issues may now seem academic, but at the time they were of great practical importance, in that they would have a direct bearing on the design of the new Tay Bridge, and even on the design of the bridge over the Firth of Forth.
WHAT CAUSED THE FALL?
Both at the time and in subsequent years differences of opinion as to the cause or causes of the disaster have arisen. Indeed no sooner had the President of the Board of Trade, Lord Sandon, announced the setting up of a Court of Inquiry, than the Board was inundated with letters from members of the public offering their explanations of the calamity. Some of these contributions were engagingly dotty, some blatantly vindictive, and several well-informed and constructive.
‘It may be found,’ suggested one Elisabeth Dean, ‘that electricity has been the cause of the destruction of the Tay Bridge.’ What she seems to have had in mind was that ‘The iron of the bridge could have become during the cold weather a strong negative. In the journey from Edinburgh the train by friction would have collected much electricity thus becoming positive and the living bodies of the passengers being positive too, then when the centre of the bridge was arrived at, this frictional electricity would upset the electrical equilibrium.’ W.E. Surtees, writing to Rothery, smelled corruption. He had owned a few shares in Hopkins, Gilkes & Co., but the company had gone into liquidation as a direct result of involvement in the Tay Bridge venture. Surtees had found out that the company had been promoted by one Joseph Dodds, MP, who had been associated with a number of fraudulent concerns. Moreover he had discovered that Bouch also had a considerable investment in Hopkins, Gilkes & Co., and he managed to suggest that the work had been skimped deliberately in order to put money into Bouch’s own pocket. E. Talbot, however, as a manufacturer with long experience of the iron trade, directed the attention of the Inquiry more usefully to the quality of the iron used in the bridge construction. He was aware that iron made in the Middlesbrough district, as the Tay Bridge iron had been, commonly ‘partook of what we in the Iron Trade call a “cold shut” property, and is therefore ill adapted to bear an unusual strain upon it.’ James Murray anticipated the views of many subsequent commentators when he expressed a ‘firm conviction, after taking into consideration the great length and height of the bridge . . . with the plan thereof, that of necessity the bridge had an oscillating tendency, especially when great or extreme pressure was brought to bear thereon. Such pressure came on 28th December last in the form of a giant hurricane bearing furiously and with tremendous force on the bridge broadside.’131
In considering all the explanations of the bridge failure which have been advanced, there remain essentially two schools of thought – those who argue that the bridge was brought down by the train, which either canted over against the side of the girders, or actually left the track, and those who believe that the bridge itself collapsed under the force of the storm, taking the train down with it. A variation on the first view – that the train brought down the bridge – is the suggestion that over time the passage of trains over the bridge caused cumulative damage to the fabric of the bridge in the form of metal fatigue in the cast-iron fixings of the columns. It was therefore only a matter of time before a disaster happened. Against that there are those who argue that the key issue was wind pressure, and the failure of the designers to make adequate allowance for the kind of gale-force winds not uncommon along the Tay estuary. Put simply, the bridge blew down. A very common view amongst contemporaries, and still popular today, was that the additional wind resistance provided by the presence of the train on the bridge at the fateful time was a major contributory factor in the collapse. As it was the cast-iron columns supporting the girders which collapsed, attention has also focused then and since on possible weaknesses in the metal of the columns, arising from poor quality iron, or poor quality control of the casting process, or both.
The leading proponent of the first theory was of course Bouch himself, who remained firmly convinced until his death that the collapse of the bridge had been brought about by one or both of the last two coaches, the second-class carriage and the guard’s van, leaning over under the force of the gale, and smashing into the east side of the girder, snapping the ties, and causing the whole column to fail. So sure was he that examination of girder no. 4, still sunk on the river bed, would prove his theory that he stayed on in Dundee until the last minute, waiting for it to be raised, before having to leave to face the Court of Inquiry, now moved to London, on 17 April. Unfortunately for Bouch, he was thwarted by Dugald Drummond, the locomotive superintendent, who insisted on raising the engine first.132
Bouch’s theory was supported, perhaps not surprisingly, by his assistant, Allan D. Stewart, and by Dr Pole, a distinguished mathematician brought in as an independent expert. In their evidence to the Inquiry they suggested that the train hit the high girders, and the shock was transmitted to the piers, which fractured and brought the bridge down. There were a number of possible objections to this theory. While it was true that scrape marks on girder No. 4 gave some colour to this explanation, it did not really fit the facts of the case. The marks were too high up the girder to have been made by a carriage simply toppling sideways off the rails. In any case, Bouch’s theory was effectively demolished by Drummond’s authoritative evidence to the Inquiry. Drummond was quite convinced that the carriages, in their headlong dive to the bottom of the river, had never left the track. He had observed in his inspection of the carriages that ‘All the vehicles had their axles bent in one direction, which to my mind points clearly to the fact that the train had not been off the rails previous to the accident to the Bridge, but remained on the rails until it reached the water.’133 In any case, acceptance of Bouch’s theory would not and did not absolve him of moral responsibility, in that he had shown himself by his own admission to be the designer of a bridge which would fall down if struck hard enough by a light wooden carriage.134
In recent years, the idea that the train brought down the bridge has been given a new lease of life by the arguments of the late Mr William Dow, a physicist who had made a special study of the bridge and its fall. Dow accepted the view that the bridge collapsed because the last two carriages came off the rails, caught on the girders, and wrenched the bridge apart. At the heart of this explanation lies the so-called ‘kink in the rails’, a distortion of the line as it entered the high girders, itself the result, according to Dow, of the accident in 1877, when, in the course of construction, two of the high girders had been blown off the top of their columns into the river. One of these girders had been written off, but the other had been salvaged, repaired and re-used. In Dow’s opinion, the girder had been weakened by its fall, had distorted in use, and since the rails were attached to wooden supports running the length of the girders, this distortion had resulted in the kink in the rails. The existence of this kink was well known to railwaymen, and had been brought to light in the course of the preliminary enquiries carried out by Thornton. It had not, however, been deemed to be sufficiently important to figure in the evidence at the inquiry.135
The plausibility of this theory does not depend, of course, on establishing a link with the 1877 accident. Whatever may have caused it there is no doubt that the kink did exist. The important question is therefore whether the kink derailed the train, and on that question there is no conclusive evidence. All the railway experts questioned about it at the time dismissed the kink as insignificant – a minor deviation which had had no effect on the running of the trains hitherto. On the other hand, the theory does square with some other evidence, not all of which came before the Inquiry. There was the assertion by the stationmaster at Newport, for instance, that he has seen, lying on the beach, a length of wooden planking from the floor of the bridge showing clear marks of the wheels of the train, suggesting that derailment had preceded the bridge’s collapse. Incredibly he failed to secure this vital piece of wood, which was allowed to float away on the tide. There is also the undoubted fact that the coupling joining the second class carriage to the one in front was found to be broken, suggesting that it had been wrenched apart by some considerable force, such as might have been applied if the carriage had caught on the girders. There are the marks on the east side of the girders which Bouch had relied on to support his own theory. At the very least they suggest that train came into contact with the girders at some point, even if it cannot be proved that such contact occurred before the bridge actually fell.136
More recently Bouch’s and Dow’s explanation of the fall was taken up by Charles McKean, in his study of the rivalry between North British and Caledonian railways – Battle for the North – published in 2006. His description of the last moments of the passengers, train and bridge is dramatic:
Barely a minute after leaving Barclay’s cabin on the south shore, passengers on the train had probably felt an unusual jolt or bounce – a very sharp one in the case of the second-class carriage at the rear of the train – and then perhaps a dragging motion accompanied by the squealing of wheels against rails. The second-class carriage came to an abrupt halt, smacking into a girder tie-bar, and was immediately annihilated by the heavier guard’s van behind, which mounted up over it, crushing David Jobson and his companions to death. The force caused the cast iron columns below to fracture, and the bridge began to topple downstream into the foam.137
Unfortunately there is no real evidence to support this colourful account of the last seconds of the ill-fated train. While it is true that the second-class carriage was badly damaged, the damage was all on the side facing west, while it should have been on the side facing east. David Jobson’s body was one of those recovered, but none of the recovered bodies showed the kind of injuries which would have resulted from the crushing force described by McKean.138 Moreover, what this explanation does not fully take into account is the evidence of eyewitnesses as to the force of the wind at the time of the fall. Virtually every account links the collapse of the bridge with an enormously powerful gust of wind, a gust which forced all observers who were not indoors at the time to turn their backs on the wind or take shelter from it, at exactly the moment at which the bridge fell. Virtually every explanation of the collapse does likewise. In the edition which came out shortly after the disaster, the Scotsman reported that once the train had reached the mid-point of the high girders, ‘at that moment a gust of wind more violent than any that had preceded it was experienced, and simultaneously the spectators noticed three separate streams of fire descend from the bridge elevation and disappear in the water, total darkness falling.’139 The deck-watch on the Mars had been forced to turn his back on the bridge by the force of the wind. It is surely taking coincidence too far to suggest that the train was derailed by the kink at exactly the same instant as it was caught by a gust of wind.
Then there was the remarkably frank admission of Albert Grothe in the course of the Inquiry that despite all the assurances he had frequently given to Dundee audiences as to the ability of the bridge to withstand the force of any wind, however powerful, nevertheless he was now quite convinced that the bridge had simply blown down. James Brunlees, an engineer who, along with John Cochrane, had been brought in by the North British after the fall to carry out an investigation on the company’s behalf, also supported this view in terms which remind us of the accounts of W.B. Thomson of the night the bridge came down. ‘It appears to me,’ Brunlees reported to his employers,
that the immediate cause was an excessive wind force acting partly upwards on the floor of the bridge and horizontally on the piers, and girders and train. An undue stress was thus thrown on the three eastern columns of the piers tending to rupture the bracing between them and those on the western side, and from the position in which the wrecked train was found I believe no. 5 of the fallen piers was the one which succumbed to the undue strain thrown on it and fell, dragging after it the whole of the large spans.140
It is of course the central tragic fact of this whole story that the bridge collapsed as the train was passing over the navigation spans, and it is not surprising that a good many explanations of the fall link those two facts together. According to one contemporary account, so long as nothing was on the line,
the westerly wind passed freely through the latticing . . . and thus the slender structure remained almost unshaken by the fiercest wind strokes, but the moment that the train entered upon this portion of the bridge the conditions of the conflict were entirely altered. Not only did the quickly rolling body weaken the resisting power of the bridge by adding the sum of the vibration to that caused by the impact of the wind but, fatally as it happened, it presented also a solid body, upon which the strength of the wind could be exercised. This, it may almost be concluded, was the cause of the lamentable occurrence.141
One of the most interesting contributions in recent years to the debate on the reasons for the bridge failure has come from Dr David Smith, a lecturer in civil engineering, who has argued strongly in favour of the view that the bridge simply blew down. Smith noted that of the main components of the bridge, both the girders and the foundations were essentially sound. Many of the 72 undamaged girders were retained in the structure of the new bridge and have lasted perfectly well for more than a century, while the foundations also have withstood the ravages of weather and water. It was the braced cast-iron columns which failed. He noted also that the columns and braces were defective to some extent – the cast iron of the columns was not of the first quality, some of the wrought-iron bracings were imperfect, and some of the lugs to which the bracings were attached were unsound.
That said, he found that there was no evidence to suggest that ‘either the columns or the bracings fell severely short of the strength they would have had if perfect’, and having scrutinised the results of tests on both bracings and columns carried out after the fall, concluded that ‘none of these figures justifies severe strictures on the quality or consistency of workmanship.’
‘Calculations made after the disaster,’ went on Smith,
showed that a wind pressure of 1675 Newtons per square metre [34.99 lbs per square foot] would have been sufficient to rupture the weakest bracing, even assuming that 20 per cent to 25 per cent of the wind force was taken by the bending stiffness of the cast iron columns, and assuming the leeward girder to take 50 per cent of this pressure. It is difficult to see how the columns could take so large a pressure with all the bracings intact. If the share taken by the columns is neglected, the pressure to break the weakest bracing becomes at most 1340 Newtons per square metre [27.9 lbs per square foot].
Further calculations showed a high probability that this pressure of wind would be exceeded in the Dundee area at least once in every 50 years. From these two sets of figures Smith concluded, ‘there is no reason to doubt that an extreme gale could have ruptured the weakest bracing. Once the weakest was ruptured the bracing on the opposite pier would be subjected to a force greater than the strength of the strongest bracing’, and the collapse of the bridge would be the inevitable result. In short, Smith fully endorsed the findings of the first report of the Court of Inquiry, that ‘the fall of the bridge was occasioned by the insufficiency of the cross bracing and its fastenings to sustain the force of the gale.’
Dr Smith’s conclusions were given further support by a computer analysis of the bridge design carried out by Tom Martin and Professor Iain Macleod of Strathclyde University. According to their calculations, and using data supplied to the original Court of Inquiry, at a wind force of 10-11 on the Beaufort scale, simultaneous toppling and bracing failure were to be expected, with bracing failure the more likely outcome. This failure would very likely have occurred even without the additional wind resistance provided by the train. An interesting feature of their analysis was that the maximum wind bracing load was found to be part-way up the columns, rather than, as might have been expected, at the base. This conforms to an extent with what actually happened, where some of the columns fractured several feet from the bottom end.142
The consensus among many modern commentators is therefore that given the design of the bridge, the cross-bracing of the cast-iron columns was bound to fail if subjected to a force of wind equal to or greater than the gale which attacked it on 28 December, 1879. To that extent, their calculations, experiments and simulations have gone a long way to reinforce the principal conclusion of the Inquiry. It is important to stress, however, that it was not the tie bars themselves, but rather the lugs on the columns to which the tie bars were attached, which actually failed. John Cochrane, in his evidence to the Inquiry, confirmed that ‘in the cases I have seen, I do not think I found any tie bars broken at all, practically it is the lugs that have gone.’ Yet William Pole and Allan D. Stewart, in their technical report to Bouch in February 1880, had calculated that these lugs should have been capable of withstanding a load of 63 tons, and therefore a wind pressure well in excess of that exerted by the great gale. Even more mysteriously, as we have seen, the evidence of tests carried out by Mr Kirkcaldy and reported to the Inquiry, revealed that the lugs he had tested had broken at very much less than 63 tons – some of them at less than one third of that figure. Pole, when questioned by the Court, accepted the test results, but was quite unable to explain them. ‘My statement,’ he told the Inquiry,
simply amounted to this: that an engineer designing these lugs might on the ordinary rules expect them to bear 63 tons, with an average quality of iron. I know perfectly well that they have broken at Mr Kirkaldy’s with less. I do not pretend here to explain why. Whether they have been damaged or not, I do not know, and I have no means of knowing. But the inference from that . . . is that the tie would break with a wind pressure of about 40 lbs.
Of course it is possible that Pole suspected that the low strength of the tie assembly was due to the conical seating for the bolt on the lug, but did not say so in order to protect Bouch. Pole was not the only witness before the Inquiry to be baffled by the test results. Edgar Gilkes, with much more experience of iron casting than Pole, confessed that the results
puzzle me a good deal. They do not agree with the tensile strains we get from other parts of the same metal; that is to say the other parts of the same column, and I do not see any good reason for the difference unless it be that those lugs had undergone a severe straining before, and were not equal to what might have been expected from them afterward.
From this is would appear that Gilkes did not understand the amplification of the stress which would occur with conical seating of the lugs, and his suggestion that the metal was weaker in the lugs is not supported by any evidence. It is tempting, of course, to explain the failure of the lugs, as many previous commentators have done, in terms of poor workmanship at the Wormit Foundry. There is no real evidence for this either. While there might be the suspicion that the practice of ‘burning on’ the lugs accounted for their weakness, managers and workmen from the foundry had stated again and again that no columns with burned-on lugs had been incorporated in the structure of the bridge. While it is possible that they were lying to save their own reputations, no less a person than Henry Law, the Board of Trade’s special investigator, conceded that in his examination of the broken parts of the bridge he had found no lugs that had been burned on. As we have seen, Yolland and Barlow attributed the great difference in strength between the metal of the columns and that of the lugs to the ‘nature of the fastenings, which caused the stress to be brought on the edges or outer sides of the lugs, instead of acting fairly upon them.’
There remains one other explanation for the failure of the lugs which has attracted attention in recent years – the phenomenon of metal fatigue – a phenomenon unknown to engineers of Bouch’s day, but suggested to the author by Mr William Dow some years ago.143 More recently the issue of metal fatigue in the iron castings has been addressed in some detail by Dr Peter Lewis of the Open University, and his colleague Ken Reynolds, a forensic metallurgist.144 Like Dow, they focus their attention on the ‘kink’ or, as they put it ‘a slight misalignment of the track’. Trains passing over this kink, they argue, induced lateral oscillations in the high girders section of the bridge. Over time, as the joints holding the bridge together became progressively loosened, these oscillations became more pronounced, resulting in fatigue cracks appearing in the cast-iron lugs, until finally the lugs gave way and the result was a catastrophic disaster. While they accept that wind loads contributed to the collapse, their argument is that the bridge was already seriously defective before that event.145
To support their theory, they revisited the evidence produced at the Inquiry, and paid particular attention to the photographic evidence, especially that relating to the cast-iron lugs whose failure lay at the heart of the disaster. ‘Close inspection of the fractures showed that they were not drilled out to give a parallel bearing surface for the bolts. On the contrary, the holes were cast as one with the lug and columns, and given a taper. This,’ they assert, ‘was a serious design defect, because it produced a severe stress concentration . . . when the bolt was stressed during straining of the bracing bars. The effect must have been to raise the stress at the outer edge of the hole by well over three times the nominal applied stress.’ They also noted Henry Law’s testimony to the Inquiry, in which he had pointed out that the bolts used to attach the tie bars to the lugs were too thin – only one and an eighth inches in diameter to fit the narrowest part of the tapered hole of one inch and a quarter. ‘The bolts were therefore a very loose fit, inducing another stress-raising factor into the equation.’ According to John Rapley, Bouch had agreed to Grothe’s suggestion to use thinner bolts as a cost-saving measure.146 If so, it was to prove a very costly mistake.
Even before the actual collapse of the bridge, there was evidence from men working on the bridge of severe vibration when a train passed over, both lateral oscillation and vertical movement – sufficient to cause water in a bucket to overflow the rim. And then there was the testimony of the unhappy Mr Noble, who had noticed the chattering in the structure, and had, as he thought, cured the problem by forcing metal shims into the loose joints. His evidence to the Court was dramatic:
– Did you discover whether any of the ironwork of the bridge was getting unstable or loose?
– In taking those soundings I spoke of, I noticed or heard a chattering of the bars.
– Tell me what it was you found to be wrong with the bars on your examination of them.
– I do not know whether I can explain it to you. I found that the cotters in coming together had got a little loose – there was not a sufficient width to get a good grip, and they had got a little loose.
It should be explained at this point that joints in the form of gibs and cotters were used only, in the structure of the Tay Bridge, to secure the lower end of the diagonal ties to the cast-iron lugs on the columns. They had a particular purpose – to enable tensioning of the tie bars on fitment by knocking the cotters together, this tensioning serving to stabilise the towers. By forcing pieces of iron bar into these joints, Noble had jammed the joints into a fixed state, bearing little or no strain from the tie bars. It was reckoned that Noble may have doctored as many as a hundred and fifty joints in this way.
Lewis and Reynolds conclude from this survey of the evidence that the bridge was already in a poor state even before the fateful night. Poor design, especially in the form of the conical holes in the lugs, poor maintenance, dangerously so, had resulted in a progressive loosening of the joints, and with it the destabilisation of the cast-iron towers. The action of passing trains, the regular battering of the malformed rail, induced metal fatigue in the lugs which then broke. In their view, while conceding that the force of the wind may have been a contributory factor, it was no more than that, the eventual disastrous outcome being well-nigh inevitable.
And what of the wind? We have seen how research published in 1993 by Tom Martin and Iain McLeod had come to a very different conclusion. In their view the action of the wind, and the failure at the design stage to build in a sufficient allowance for wind pressure, were the overriding factors in explaining the collapse of the bridge. If Lewis and Reynolds are adherents of the ‘train brought down the bridge’ thesis, then Martin and McLeod represent the view that the bridge simply blew down, taking with it the train. In 1995, and again in 2004, they have returned to this issue making use of the latest research methods, and arriving at much the same basic result.147 We have to ask the question, wherein lie the very fundamental differences between Lewis and Reynolds on the one hand and Martin and McLeod on the other, to explain this very different set of conclusions?
We need to focus on two issues in particular – the pressure of the wind on the night in question, and the evidence for metal fatigue in the cast-iron lugs.
On the issue of wind pressure, Lewis and Reynolds have gone back to the testimony presented to the Inquiry, and in particular the opinion of one expert witness, Benjamin Baker, later to be one of the designers of the Forth Bridge. Experts had calculated that a pressure of around 35 pounds per square foot would be required to topple the high girders, but Baker’s conclusion, after making a detailed survey of damage to walls and buildings in the vicinity, was that wind pressure on the night could not have been more than 15 pounds psf – far less than the predicted toppling pressure.
There were indeed no accurate scientific instruments present in Dundee at the time of the fall to measure the pressure of the wind, so the Inquiry had to rely on the views of unofficial observers, and these observers were largely agreed on a wind pressure of between 10 and 11 on the Beaufort scale. Martin and McLeod’s calculations are based on a wind force of this order, which they present as between 28 and 36 pounds per square foot. This pressure of wind, they conclude, would have been sufficient to bring about an uplift in the base of the outer column on the windward (west) side of the bridge. The main effect of this uplift was to increase significantly the tensile load in the diagonal bracing members, leading to their failure. To quote from their 1995 article:
On the basis of these observations a scenario for the collapse is as follows. When the train reached the high girders there was a particular strong gust. The presence of the train increased the overturning effect marginally, and the bolts in the windward columns came into tension. Because they were intended for location purposes rather than to take tension, they were not fully anchored into the masonry of the pier. The column bases started to lift off taking two courses of masonry with them. This had the beneficial effect of reducing the loads in the baseplate bolts, but caused a significant increase [of tension] in the diagonal bracing members, causing them to fail. These members first failed not at the bottom level [of the towers] but at a level above that. This triggered a toppling collapse with rotation tending to be at level 1. During the process of toppling there was a kickback to windward on the remains of the piers below level 1.
This graphic account of the sequence of events has the merit of conforming closely to the evidence presented to the Inquiry, both verbal and photographic. As we know, however, a key element in the failure of the bridge was the breakage of the cast-iron lugs – explained by Lewis and Reynolds as due to metal fatigue. Is it possible to reconcile the two rival interpretations by explaining the vulnerability of the bridge to severe wind pressure as due to the inherent weakness of the lugs caused by metal fatigue? The answer to that is ‘probably not’. Martin and McLeod have no doubts that the disaster would have taken place even if the structure had been in perfect condition in accordance with the specification. The fundamental flaws in the design for the bridge were the failure to make adequate allowance for wind pressure, and the inadequate specification for the tie assemblies, or, as they put it in their 2004 paper, the applied wind load was much greater than the design wind load, and the actual strength of the ties was significantly less than the design strength of the ties, both with respect to the lug failure, and the failure of the tie itself.
Nor do they accept the case for the effects of dynamic motion and the onset of metal fatigue as presented by Lewis and Reynolds. Drawing on the results of modern research into the failure of cast-iron castings due to metal fatigue, they conclude that the repeated stresses experienced by the component parts of the bridge over its lifetime would have been insufficient to cause fatigue. Nor do they accept the argument advanced by Lewis in his full-length book on the subject, that the fact that the collapse affected the high girders only was due to the absence of lateral girders, tying together the towers supporting the high girders.148 Once again we are presented with the conclusion that the fundamental errors were to make inadequate allowance for wind pressure, and in the lug specification. All other explanations are mere footnotes to these facts.
THE QUESTION OF BLAME
It is one thing to arrive at conclusions as to the causes of the bridge failure, but it is, or may be, quite another to assign blame. Rothery’s separate report, as we have seen, did both, and laid the blame for deficiencies of design, construction and maintenance mostly, though not entirely, as Bouch’s door. Even Smith, who was sympathetic to Bouch and criticised Rothery for the extravagance of his attack on the bridge’s designer, accepted that the reason for the collapse of the bridge was that Bouch did not make any specific allowance for wind force in his calculations. It remains open to question how far Bouch should be blamed for this, and whether others besides him should shoulder at least some of the moral responsibility for the disaster.
In the first place it is not strictly true that no allowance for wind pressure was made in the bridge’s design. It is clear from the report of William Pole and Allan D. Stewart, submitted to Bouch on 25 February 1880, that Stewart had indeed made some allowance for wind pressure on his own initiative, though the allowance he made of only 20 lbs per square foot was clearly insufficient.149
At the Inquiry Bouch seemed curiously unaware of this fact. More to the point, there is clear evidence that in October 1869, when the bridge was still at the design stage, Bouch had made a written enquiry to the Board of Trade, asking what allowance should be made for wind pressure on lattice girders of up to 200 feet in length. (This was of course before the decision was made to increase the length of most of the girders to 245 feet.) Irony of ironies, his query was dealt with by none other than Colonel Yolland, who blandly informed him that ‘we do not take the force of the wind into account when open lattice girders are used for spans not exceeding 200 feet’. No wonder that Yolland was unwilling to put his name to Rothery’s attack on Bouch. Moreover, at the time when Bouch was obliged to redesign the bridge to take account of the new information about the nature of the river bed, he was also in the process of designing the Forth bridge, whose spans were to be a massive 1,600 feet long. Bouch took the precaution of consulting five of his most eminent colleagues in the profession (one of whom was W.H. Barlow, the third member of the Court of Inquiry) about the correct allowance for wind pressure, and it was they who then consulted Sir George Airy, the Astronomer Royal. The latter’s recommendation of 10 lbs per square foot was used by Bouch to check the design of the Tay Bridge.150
It is true, as the Inquiry itself was told, that in France the usual allowance was 55 lbs, and in the United States, 50 lbs, but that information does not seem to have been widely known in Britain. It is difficult therefore to accept Rothery’s view that Bouch should bear all the blame for a failure in design when, by all accounts, he had taken careful steps to acquire the latest information on the subject from the very experts who were later to sit in judgment on him.
Not that even Rothery assigned all blame exclusively to Bouch, and the Inquiry had revealed failures to fulfil their responsibilities on the part of almost everyone called before it who had had a role in its construction. The contractors, Hopkins Gilkes, and their representative as overall manager of the project, Albert Grothe, were criticised for their failure to construct the bridge to the necessary standards. Lesser figures, like Camphuis and Ferguson, were shown to be incompetent, and even honest Henry Noble, striving to do more than he was asked or qualified to do, had seriously failed to recognise his own limitations.
Yet should the real responsibility lie, not with these lesser men, but with their employers? Should not the North British, and its directors and shareholders, shoulder their share of the blame? Evidently the Scotsman thought so, and on the morning after the publication of Rothery’s report weighed in with an attack on the Company for failing to exercise adequate supervision of the bridge’s construction:
There was evidently a degree of carelessness in the matter of supervising the bridge which was culpable and even scandalous. Sir Thomas Bouch may be to blame for not having looked after Henry Noble; but ought not someone to have seen that Sir Thomas Bouch attended to his duty? Can the railway company be freed from blame? It is very difficult to do so . . . it is clearly the company and the company alone that must be held answerable to the public for whatever carelessness there was in the supervision and maintenance of the bridge.151
If it had chosen, though it did not, the Scotsman might have found other reasons to blame the company. It was the North British which had employed Bouch in the first instance – a man who had made his reputation as a designer of railway lines which were, like the St Andrews line, notable for their lightness and cheapness. He had also, by the time he came to design the Tay Bridge, acquired something of a reputation for unreliability. The company secretary of the small Leven line, of which Bouch was the designer, had endless trouble with him for failing to produce plans, to inspect completed sections of the line and to attend important meetings. In one of his plans, the measurements of every field were incorrect, and it had to be returned. ‘Mr Bouch’s want of attention to our present interests,’ complained the harassed secretary, ‘is a matter beyond our comprehension.’ Similar problems were encountered by the promoters of the Crieff line, who also made the mistake of employing Bouch. While it is possible that the directors of the North British knew nothing of these problems, they should have done. When the company formed to extend the Leven railway along the Fife coast heard of the problems which had arisen with the Leven line, they decided to dispense with Bouch’s services. It is perhaps worth noting also that Bouch’s plans for Dundee’s tramway system came in for severe criticism from the leading consulting engineers of the day.152
All along (except when it came to lavish self-congratulatory lunches) the North British had sought cheapness as the expense of durability. They had refused to fund the bridge itself, and passed that responsibility to the local men of the Undertaking; they had opted for a narrow and insubstantial single-line bridge, in place of a sturdier double line, solely on grounds of cost, and in the face of a good deal of local criticism. It is with a certain amount of grim satisfaction one notes that in the end it cost the North British something of the order of £1 million to bridge the Tay estuary.
And then again, the Inquiry, in casting counsel for the Board of Trade in the role of inquisitor, had pre-empted the question of the Board’s own responsibility. There was not just the matter of Yolland’s advice to Bouch, but there was also the whole question of the Board’s inspection and approval of the bridge in 1878. At a meeting of the Institution of Engineers and Shipbuilders in Scotland held in Glasgow early in 1880, the speaker, St John Vincent Day, exclaimed:
I fail, in view of what I have seen for myself of the character of the structure, to comprehend how Major General Hutchinson could report that ‘the iron work has been well put together in the columns and the girders’? Did he ascertain the depth and variation in depth of the holding down bolts? If so, his report is, to say the least, incorrect, for it has been abundantly shown how unfit was the structure of the columns for the functions imposed on them.153
The unfortunate Hutchinson had indeed been called to give evidence at the Inquiry, where he was forced to concede that his inspection had been superficial, and that he had not tested the bridge for the effects of wind pressure. In a separate report to the Secretary to the Board of Trade, Hutchinson insisted that he had found nothing wrong with the bridge during the three days of his inspection, and reminded the Board that at the time he had stipulated a speed limit of 25 m.p.h. It was not his fault if drivers ignored this restriction. On the matter of wind pressure he claimed that ‘I was anxious to see how the lateral stiffness of the piers might be affected by the action of a high wind upon the side of a train in motion over the bridge. This I had intended to get if possible an opportunity of doing before the traffic commenced running, but I was laid aside by a serious illness shortly after the inspection and before my recovery the bridge had been opened to traffic.’154 To fall ill was hardly Hutchinson’s fault, but there had been nothing to stop Yolland sending a replacement inspector, which he had failed to do.
Not surprisingly, the failure of the bridge so soon after it had been passed as sound by the Board of Trade aroused considerable public concern. In his report Henry Rothery had defended the Board’s position, and in the House of Commons debate on the fall of the bridge, President of the Board Joseph Chamberlain felt obliged to defend his Inspectorate on grounds of general principle. Hutchinson, he argued, ‘could not be held responsible for any defects in the Tay Bridge which were not discoverable in such an inspection which he was empowered to make . . . still less for defects which did not exist until after the inspection.’ Moreover, Chamberlain insisted,
the duty of an inspecting officer, so far as regards design, is to see that the construction is not such as to transgress those rules and precautions which practice and experience had proved to be necessary for safety. If he were to go beyond this, or if he were to make himself responsible for every novel design, and if he were to attempt to introduce new rules and practices not accepted by the profession, he would be removing from the civil engineer and taking upon himself a responsibility not committed to him by Parliament.155
Plausible perhaps, but not altogether convincing.
And yet, and yet. Even if it is accepted that others – both individuals and organisations – should share the blame with Bouch, it remains true that he was both legally and morally responsible for the failings of his design. It has been argued that in the matter of the underestimate of the allowance for wind pressure, for example, Bouch had taken reasonable precautions to enquire of the experts how much allowance should be made. It is difficult, however, to absolve him of all blame in the matter of those wretched cast-iron lugs. The Report of the Inquiry stated bluntly that
it was in casting the holes through which the bolts, which held the ends of the struts and tie bars, passed, that the greatest mistake was made. These holes were cast in the lugs, and were already made, when they issued from the mould. We were told, however, that it is almost impossible to prevent the workers from casting the holes conical, as the cores can then be more readily removed, and accordingly we find that the holes in the lugs were for the most part, if not entirely, cast conical. The result was that the bolts, instead of having a plain surface to rest upon, as they would have had if the holes had been drilled or made cylindrical by riming, or drilling, bore only on one edge, and when a strain came upon them, they would of course give, until they got a bearing upon the sides of the holes.
In a very damaging exchange with Rothery, Bouch was forced to concede that the holes should indeed have been cylindrical, and that the bolts should have been wide enough in diameter to fill the holes. As it was, not only were the holes both conical and irregular in shape, but the bolts were appreciably thinner that the holes.
The effect of these three things, namely the giving of the bolts so as to get a bearing on the sides of the holes, the irregularity of the holes in shape and position, and the holes being larger than the bolts, was to give a certain amount of play to the ends of the ties and struts; so that it was found, under Mr Kirkaldy’s tests, that when the force was applied in the same direction as when in position on the columns, and by a steady pull without any shock, the lug was able to bear only one third of the pressure, which it should have done according to the amount of its sectional area.156
As we noted, one of Bouch’s previous and supremely successful bridge designs had been the Belah Viaduct. So far from collapsing, the Belah survived for many years of successful service, and fell prey in the end not to metal fatigue or to the pressure of wind, but to the axe wielded by Dr Beeching in the 1960s. It too was constructed of cast-iron columns, and was very much taller than the Tay Bridge. But it differed from the Tay Bridge in three vital respects. First, its girders were much shorter, and their supports much closer together; second, the ‘legs’ of its supporting towers were much wider apart at the foot than they were at the top – what engineers call ‘batter’; and third, its tie bars were not connected to the columns by cast-iron lugs at all – but by hoops of wrought iron which encircled the columns. At the Inquiry, Bouch was asked by Barlow why he had deviated from the method for dealing with the horizontal ties he had used so successfully at Belah, to which he replied ‘They were so much more expensive, this was a saving of money.’ But at what ultimate cost?
For this failure, it is difficult to absolve him from blame. The author has been in correspondence with a group of eminent civil engineers, and it is worth reproducing their views here verbatim:
The critical faults in the design of the bridge were a) the underestimate of the wind forces on the structure, and b) the unsuitability of the tie assemblies. In relation to a) there were no written UK rules for wind loading when the Tay Bridge was designed. Therefore whether Bouch should be held negligent for using a low value for the wind force on the bridge is open to question. He knew it was an issue that should be considered but rather than play safe and use a high loading he used a low loading.
As to the design of the ties, whether or not there were written rules for connecting ties to columns (probably not), Bouch understood the fundamental principles of how to make such connections in a competent way, as evidenced from his design for the Belah Viaduct. He knew it was better to make a wrought-iron collar around the column and attach the ties to that. He knew that for best strength one should arrange that the bearing of a bolt on a support should be smooth and parallel to the line of the bolt – an elementary engineering principle. But he did not use these principles in the design of the connection to the column for the piers of the Tay Bridge. He compromised his own standards by allowing the bolts to bear unevenly on the cast-iron lugs because ‘this was a saving of money’. He had staked his reputation on providing a low-cost bridge for his clients. Costs had already increased very significantly due to the early problems with the foundations, and he shaved down the redesign. He set the interests of his clients above that of the integrity of the bridge. One can say that his clients should not have pushed him in this direction, but that does not remove the responsibility from Bouch. It is a very difficult decision to make, but the code of ethics of professional engineering requires a consultant to refuse to continue with a client brief if the risk to the public becomes unacceptable. Bouch took a risk to save his reputation (for designing low-cost bridges) and put the interests of his client and himself above those of the public. That, in our view, made him guilty of negligence.157
EXIT SIR THOMAS BOUCH
It is hardly surprising that the Board, like everyone else involved, should disclaim responsibility, or that Chamberlain, like Rothery, should hold Bouch responsible. ‘At the present moment,’ Chamberlain assured Parliament, ‘there is no one more deserving of pity than the civil engineer who designed and constructed the Tay Bridge and who also, as the law now stands, is held responsible for its defects.’158 The question is, what did this all but universal condemnation have upon the unfortunate designer of the bridge, and how did he react to it?
The last day of the hearings before the Court of Inquiry was 8 May, a Saturday, and almost two months went by before its report was published. During those two months, Bouch worked on normally. Uppermost in his mind was the reconstruction of the Tay Bridge, which would require from him new plans for submission to Parliament, but there was also the great undertaking of the planned bridge over the Forth, not to mention the final piece of the east coast route – the bridge over the South Esk at Montrose. There seems to have been no doubt in his mind that he would continue to be responsible for all three projects.
Others were less confident. On 13 May, the North British board met in Edinburgh to consider the situation. One of the items for discussion was a letter from Adam Johnstone, chief solicitor for the North British Railway Company, suggesting that Bouch be got rid of, and the plans for the replacement be entrusted to a new engineer. At the time the board was not prepared to abandon Bouch, and George Wieland was instructed to send Johnstone a telegram affirming the board’s position that Bouch must continue to be associated with the parliamentary plan for the reconstruction of the bridge.159
What Bouch now proposed was to improve the stability of the reconstructed bridge by reducing its height by 30 feet. The estimated cost of this plan, however, came to more than the sum allocated by the board for the reconstruction, and Bouch wrote to Johnstone on 17 May to suggest that the approach to Parliament should consist of a plan showing the bridge at its present height, but allowing for a reduction of up to 40 feet, once there was money to pay for it. Johnstone advised against this, and after more discussions between Bouch, Stirling, Falshaw and Walker, it was agreed to submit plans based on a reduction of 30 feet, but with the option of a further reduction to a total of 40 feet. Johnstone duly set to work on the draft parliamentary bill, but with little enthusiasm. More in touch with political opinion than most of his colleagues in the company, Johnstone had long been convinced that no proposal with which Bouch was associated would now be acceptable. Perhaps the senior members of the board understood this also, but were ashamed to be seen publicly to jettison Bouch. Privately they discussed the possibility of submitting the plans without his name on them. On 2 July the bill for the reconstruction of the Tay Bridge was introduced into the House of Lords, and allowed to pass standing orders unopposed, but with a warning to the company from Lord Riddesdale that it was likely to meet with opposition from both Houses in the following week. Three days later the news of the Court of Inquiry’s two reports hit the headlines.160
The terms of these reports, especially Rothery’s, must have been a severe blow to Bouch, but his first reaction was to stick to his guns. On the same morning, 5 July, he sent a telegram to Johnstone: ‘Have seen report on bridge but am still going on completing my proof according to the deposited plans to enable you to complete your brief to counsel.’ He then went round to see his solicitor, A.J. Dickson, whose sympathy for Bouch’s feelings comes out strongly in a letter he wrote to Johnstone immediately after the meeting.
What an unmerciful report this is that has emanated from the Court of Inquiry. It seems too severe in every sense to be just . . . this report magnifies and rides to death (particularly the Wreck Commissioner’s) every fault that can be picked and makes little allowance for the judgment of others and the possible imperfections, ignorance, or want of unbiased vision on the part of the Reporters themselves in a matter which could in all essential parts remain a mystery until the end of things.
Dickson was also angry on Bouch’s behalf that Rothery had written his report in terms which suggested that his views were shared by Barlow and Yolland. Accordingly he wrote to Yolland, asking for clarification. ‘Sir Thomas Bouch’s position is under any circumstances sufficiently painful, and we are entitled to ask you to state in justice to him whether Mr Rothery was warranted in so representing your opinion as concurring with his in matters referred to you in this report.’ To which Yolland and Barlow replied jointly that ‘Mr Rothery was not warranted in representing our opinions as concurring with his own in matters not referred to in our report.’161
Bouch could be defended, but he could not be saved. In London Adam Johnstone, trying to prepare the ground for the discussion of the Tay Bridge Bill in Parliament, knew that it would face a hostile reception, and was convinced that Bouch would have to be dropped. He said as much in a telegram to the North British board, to which Wieland replied on their behalf that ‘While we cannot entirely overlook Bouch, it is clear that independent engineers must be appointed for the Tay work.’ John Stirling also took a pragmatic view, and in a letter to Johnstone told him that
I should be very sorry to throw Bouch over altogether, but if it comes to a question of losing our bill we cannot help ourselves. This is my individual opinion. I was quite satisfied all along that although we might employ him to get our bill through parliament, yet to secure public confidence the plans, whatever they are, must have the sanction of a first class engineer, and I consider that Barlow, from his connection with the Tay Bridge Inquiry was the best man we could get.162
Even so, the North British found it difficult to bring themselves to tell Bouch to go. John Walker wrote to Johnstone on Bouch’s behalf, suggesting, pointlessly, that while control over the bridge project must be put in other hands, Bouch’s name might still be associated with it. Bouch himself was beginning to face up to the vulnerability of his position. Johnstone had written to him explaining the situation somewhat bluntly, and to this Bouch replied in a telegram that he ‘had arranged to send up an assistant with bridge plan completed according to your parliamentary deposited plan, but after your letter suppose I had better wait reply.’ That evening in the Commons both the promoters of the bill and Bouch in particular were subjected to a vitriolic attack from Mr Anderson, reputedly acting on behalf of the Caledonian Railway. ‘The House has now to consider,’ fumed Anderson,
whether under these circumstances they ought to allow the very parties who are to blame to come to the house in the last month of the session and endeavour to rush through parliament a bill not for the construction of a new bridge under the supervision of new engineers, but a bill for the patching up of the miserable old structure. I myself have seen the plans and specifications, and they bear the name of Sir Thomas Bouch. Instead of coming to the house for a bill I think that some of the parties might rather be standing in a criminal dock to answer for their negligence.
Although the bill was granted a second reading, Bouch’s position was by now untenable. Under authority from the North British board, Johnstone took action, appointing James Brunlees as the engineer for the reconstructed bridge, and telling Bouch what he had done, leaving him with no option but to resign. ‘After the letter of yours dated the 13th,’ Bouch duly responded, ‘I must consider my position as engineer for the Tay Bridge to be terminated.’163
Time was running out both for the bridge and for Bouch himself. Parliament threw out the Tay Bridge Bill, and the Company, made aware that no scheme with Bouch’s name attached to it had any chance of success, applied successfully to be allowed to withdraw their plans for a Forth Bridge. The great east coast dream which Bouch had harboured throughout his career was apparently over.
Bouch himself did not long survive this final disappointment. Although for a time he continued to work in his Edinburgh office on his few remaining projects, and he travelled to London at the end of July to defend the bill for the Edinburgh South Side and Suburban Railway, on the day after his return he fell seriously ill. On medical advice his wife took him to the Border town of Moffat to recuperate, but without success. Bouch died on 30 October, 1880, aged only fifty-eight, having survived the fall of his great bridge by only ten months.164