The Forth Bridge… built for the ages

Imagine… You’ve drawn and redrawn dozens of designs, consulted countless experts about your plans, worked with officials to secure approvals. And now, at last, the first day of construction has dawned. How do you feel? A mix of relief, excitement and also some terror. This has got to work…

That day and these feelings came for the designers, engineers, and constructors of the Forth Bridge on 6^th June, 1883. If you’ve followed the story of the bridge through the preceding blogs, you’ll understand that behind that day lies a long history of crossing the Firth of Forth: ferries for people, animals, carts; ferries that carried trains; plans for bridges; plans for tunnels. Every major project had stalled or failed. And June 1883 is only 3 years, 5 months, 1 week and 1 day since the bridge over the nearby River Tay collapsed in a storm with the loss of 75 lives. Now they are daring to bridge the Forth?

Benjamin Baker (designer), John Fowler (consulting engineer), and William Arrol (building contractor) must have been nervous. Yet, they’d already poured their skills and hearts into this project, and their will for it to succeed was as strong as the steel with which the bridge would be built. So the work began.

Because the Forth Bridge became recognized around the world as an engineering marvel, there are mountains of technical information about its design and construction. I’ll try to keep the story moving, though mostly the remarkable engineering work at this bridge is the story. But, if the detail is too much, jump ahead a little to find what interests you.

Foundations

I was pastor of a new church in Livingston, West Lothian. Initially we met in a school but when numbers grew money was raised, a site bought, and foundations were laid for our own church building. But there was a complication for those foundations. Years before, our site had been a dumping ground for loose soil. So our contractor’s team had to dig through all that landfill until they reached firm ground, a solid base. Then, in the trench they’d formed, they poured concrete which, when set, became the foundation on which our building would rest.

In principle, that’s what they did for the Forth Bridge. But its foundations would be under water, and you can’t pour concrete into a tidal river.

So what do you do? You use caissons.

Imagine an open-ended metal cylinder. It could be a tin can without its top and bottom. Now, scale up that can to immense size, something like an old-style gasometer (UK) or a giant water tank (USA). Then picture that sunk into water, and eventually filled with concrete, and you begin to understand what holds up the Forth Bridge.

Each caisson for the Forth Bridge was 70 feet (21.3 metres) in diameter and between 50 and 90 feet (15.2/27.4 metres) high. When empty, each weighed around 500 tons. When filled with concrete they would weigh up to 20,000 tons. They were constructed on shore from wrought-iron, towed out and sunk exactly where a pier was needed.

But you couldn’t just sink a caisson and hope for the best. It had to sit solidly in precisely the right place and at precisely the right depth, with no movement whatsoever. The base of each caisson was pre-shaped for its location, but more work was needed for a perfect fit. That required men with explosives, shovels, pick axes and sledgehammers to blast and break rock so the caisson sat perfectly on the boulder clay and rock beneath the river bed.

The Firth of Forth is tidal, and the changing depth of the river created challenges for excavations inside caissons. You can’t work down a caisson with water pouring in at high tide. Some caissons could be protected by a cofferdam –a temporary circular barrier to hold back water. Then what’s enclosed could be pumped out and work done inside. But others – those near South Queensferry in particular – were under water at high tide and low tide. How could men work at the bases of these caissons?

Yk Times, CC BY-SA 3.0, via Wikimedia commons
**Schematic cross section of a pressurized caisson**

The answer was the ‘pneumatic method’. A pneumatic caisson is sealed at the top, then filled (or partially filled) with compressed air. That creates a protected space within which diggers can work. The illustration and line drawing help explain how it was done. An airlock gave workmen entry to one or two shafts down to the work area, and the mud and rock they excavated was lifted to the surface via another shaft, a ‘muck tube’.

The pressurised air flow had to be controlled precisely: a) so that the workers had an adequate supply of fresh air; b) to hold back any significant inflow of water or mud beneath the edges of the caisson.

Sonrel, L., Public Domain, via Wikimedia Commons
**Line drawing of work at base of pressurised caisson**

This was dangerous work. A failure with the compressed air would mean the workmen drown. And compressed air risked serious health problems when returning to the surface.

What they called caisson disease is what we now call decompression sickness (DCS) or the bends. Wikipedia describes it as:

‘a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving…’[1]

The workers at the bottom of a caisson were breathing air in high ambient pressure conditions and then surfacing to the lower pressure outside the caisson. Unless the pressure was reduced slowly the result would be, at least, severe joint or skeletal pain and very possibly death.

Only one death from caisson disease was recorded at the Forth, but just a few years earlier, during the construction of the Eads Bridge across the Mississippi River, 15 caisson workers died, two were permanently disabled and 77 severely afflicted because of the disease.[2]

Before moving on, imagine the conditions for these caisson workers:

they climbed down ladders into a sealed space under the River Forth;
they had no more than seven feet (2.1 metres) of headroom;
their whole shift was spent hacking at clay and rock with heavy tools, then lifting the muck into ‘baskets’ to be pulled to the surface;
if there was an emergency with the compressed air or flooding, they’d have to exit, but to escape to the surface quickly would likely kill them.

Of all miserable and risky jobs, that must rank near the top of the list.

The only humorous thing I’ve found about the pneumatic caissons comes from Murray (in his book The Forth Railway Bridge) who describes a visitor descending into the underwater chamber to see the work. Impressed, he brought out his flask, and offered the men (mostly Italians) a ‘wee dram’ of his whisky. No doubt they appreciated it. And there’s no doubt the visitor didn’t realise his flask was now full of compressed air until, that is, he climbed out of the airlock at the surface and his flask exploded.

It took three years for the caissons to be finished. They’d been filled with 21,000 tons of best Portland cement and surrounded by 740,000 cubic feet of best Aberdeen granite. But the piers are built. Now it’s 1886 and at last work on the bridge itself can start.

Superstructure

This will be a giant of a bridge:

Its overall length will be more than 1.5 miles (2467 metres)
It’ll rise almost 450 feet (137 metres) above its foundations, 361 feet (110 metres) above high tide
It’ll be made of steel weighing 53,000 tonnes (52,163 imp tons; 58,422 N Am tons)
The riggers will use 6.5 million rivets (that’s the oft-quoted number, but several experts think the real number of rivets was 7 or even 9 million)

Whole villages of huts had already been created on both shores, and on Inchgarvie island. Some of these accommodated workers, though many of the ‘briggers’ had to be transported to the site each day. There were other huts for joiners and carpenters, offices, sheds to store materials, and larger ones for the assembly of steel plates. At the busiest time for construction, the village and building site at South Queensferry covered 60 acres.

The local site was not equipped to manufacture the largest bridge parts. They were made of the best steel in foundries in Glasgow, Motherwell and Swansea. Large plates and girders were cut at South Queensferry, where a huge loft was set up so templates and patterns for those plates could be drawn ‘life-sized’ on a blackened floor.

The bridge would be of enormous weight, but not as much as it might have been. To lighten the load the major compression members were designed as tubes, using steel 1¼ inches (3.2 cm) thick and 12 feet (3.6 metres) in diameter. (As a child I remember being told that workers walked up and down inside those tubes. I wished I could do that!) The bridge designer, Benjamin Baker, said that the weight those tubes would carry (i.e., the bridge’s own weight, plus the weight of trains and wind pressure) would be the same as a transatlantic liner filled with cargo. The tubes would be held together with a web of steel girders. Expansion joints allowed for up to 18 inches (46 cm) of movement caused by temperature variations. (The photograph of the base resting on its piers provides a good close-up of the compression tubes and girders.)

A. Pingstone, Public Domain, via Wikimedia Commons
**Close up photo of bridge resting on its piers**

The first bridge section built were the towers. They had to be first because this was a cantilever bridge. Let me explain.

Here’s one description of a cantilever design: ‘This type uses a pillar anchored vertically into the ground to support a horizontal deck extending out from one or both sides across the span.’[3] In other words, a strong vertical piece is the sole support for an attached horizontal piece.

The simplest example of cantilever design involves a diving board. Usually there’s an upright tower, from which a diving platform or board projects out. All the weight is carried back down to the ground by the tower. Now – in a flight of imagination – picture two identical diving boards facing each other, with their diving platforms meeting in mid air. What do you have now? You have a bridge. You could walk across from one tower to the other, each half of the platform you’re crossing fixed to its tower.

Wilhelm Westhofen, Public domain, via Wikimedia Commons
**Small section of original bridge design drawing**

That’s almost exactly the design of the Forth Bridge. I’ve put part of an original design drawing of the bridge alongside – it shows just two towers (the rectangular vertical sections supported by X-shaped girders), each tower consisting of two pairs of pillars,[4] with upper arms stretching sideways from the top and tilting downwards. Each arm reaches track height where it supports a small ‘suspended span’ in the middle. (Further weight is taken by the lower, curved compression members.)

The Forth Bridge is actually a twin cantilever design. That sounds complicated but isn’t. Imagine standing with each of your arms stretched sideways away from your body while you hold a bag of flour in each hand. You are now a twin cantilever because you reach out in two directions. Then imagine another person stands in exactly the same posture next to you, your hands touching only to share the weight of the bag of flour you both now hold. Finally let’s add a third person, again arms outstretched and sharing the weight of the flour bag held by his neighbour. You have created the Forth Bridge. What three people can do holding bags of flour is parallel to what’s done with pillars and cantilever arms in the Forth Bridge. You can see that shape by looking now at the full-length design drawing (just below). Each tower has twin vertical pillars because their cantilever arms reach out sideways in opposite directions. Instead of a bag of flour, they each support a small span of girders where their arms almost touch. At the far right and far left the arms rest on pillars that carry the ends of the rail track to the shore.

Wilhelm Westhofen, Public domain, via Wikimedia Commons
**Full length version of original design drawing**

Of course, by major steelwork those cantilever arms (working with lower compression tubes) bear most of the weight of the whole bridge. They’re linked to the track where trains cross and to other parts of the bridge. The suspended spans between them are far lighter for those cantilever arms than bags of flour are for us.

{{PD-US-expired}} Public Domain
**View from S Queensferry, 1887 – almost the only work on the bridge at this stage is the construction of the towers**

{{PD-US-expired}} Public Domain
**View of bridge in 1888 – the twin cantilevers arms from each tower reach out, with support from a lattice of trusses**

If – hopefully – you’ve followed some of my amateur explanation, you’ll understand that the weight in a cantilever design depends on the vertical towers because they’re the only parts which rest on the foundations. Nothing else about the Forth Bridge could be built until they were in place. Even then the cantilever arms had to be added at an equal rate to both sides of the towers to ensure balance. So – as further photos show – the bridge gradually expanded outwards from each of the three towers until eventually they were within ‘touching distance’ of each other, and could be finally linked by those short spans.

One more detail. The Forth Bridge is technically a cantilever-truss design. The construction expert I quoted earlier writes: ‘Cantilever bridges are often supported with trusses. A bridge truss takes the load off the deck and transfers it to the supporting piers and abutments, helping the cantilevers withstand tension in the upper supports and compression in the lower ones.’[5] I believe he’s saying the trusses within the Forth Bridge push the weight of trains onto the larger structural members.

Accidents

Many died during construction of the bridge. In an earlier blog, I said the number was more than those drowned in the Tay Bridge disaster, which was 75. Official figures for deaths while building the Forth Bridge give a number of 73. So I was wrong – maybe. The hesitation is because sometimes men killed working on the approaches to the bridge were not counted, nor those who died later from injuries sustained while working on the bridge. Perhaps some were never counted. Of course there were also those who only nearly died, such as the eight men who fell from the bridge while working and were rescued from drowning by boats stationed in the water below. As of 2009, the official figures say this: ‘Of the 73 recorded deaths, 38 were as a result of falling, 9 of being crushed, 9 drowned, 8 struck by a falling object, 3 died in a fire in a bothy, 1 of caisson disease, and the cause of five deaths is unknown.’[6]

I said in an earlier blog that there was a surprising explanation for so many accidents. That was drunkenness. Any worker found drunk was sent off the site immediately to sober up. Otherwise he risked his own life and the lives of others. Murray’s book records that Arrol (the main contractor) considered the drinking so bad he instructed that more foreigners should be employed as they didn’t drink as much as the Scots! But drunkenness wasn’t the only cause of accidents. Apparently some of the younger briggers were foolhardy enough to ignore safety ropes and jump from girder to girder while hundreds of feet up. Not all were successful.

Most likely the high accident and death toll was simply because it was dangerous to build a bridge so high and so wide through all seasons across a wide estuary exposed to the frequently severe North Sea weather.

Finished, tested and opened

Work on the bridge was 24/7, stopping only when the strongest of winds made it impossible to be on the bridge safely. Night-time work required lighting. Gas was too expensive; oil lamps were dangerous. So they used electricity, very new at the time.[7] Occasionally it failed, leaving workers in exposed locations in darkness.

Finally the work neared its finish. The last connections had to be made when the steel was in precisely the right position, neither expanded because of a high temperature nor contracted because of a low temperature. Temporary bolts were inserted initially, and then they had to wait several days more for a good temperature. On the morning of 14^th November, 1889, everything was exactly right, and the final connection made. Thirty six temporary bolts still had to be removed, but before that could be done the temperature dropped, the bolts sheared with a sound like a cannon firing, and a small shake went through the bridge. But, as the bridge designer said later, the only consequence was that work removing 36 bolts was saved.

The official load testing of the bridge took place in late January, 1890. The test involved two trains, but each ‘train’ actually consisted of three locomotives towing 50 wagons loaded with coal. The total weight was 1880 tons, more than twice the design load for the bridge. They moved across the bridge, stopping several times for deflection measurements to be made. Nothing adverse was found. The bridge passed its test! The first official crossing took place the next month involving railway company dignitaries.

The official opening was on 4^th March, 1890. One of the guests on the day was Gustave Eiffel, the civil engineer responsible for the Eiffel Tower which had opened to the Paris public only the previous year. But it was the Duke of Rothesay, later to become King Edward VII, who hammered home the last rivet, this one gold plated. Oddly, though there are several line drawings of the opening ceremony, I believe there are virtually no photographs.

Facts from then until now

At the time of opening, the Forth Bridge had the longest single cantilever bridge span in the world. In 1919 the Quebec Bridge in Canada exceeded it, but the Forth Bridge continues to be in second place.

The total construction cost was £3 million, a huge sum in the 1880s but unsurprising for a bridge of such strength across a wide estuary. Cost is a major reason why few other bridges like it have been built.

Probably no-one has ever known the overall number employed to build the bridge. That would have to include all the staff in design, engineering and construction offices, in foundries in other cities, those who worked on approach piers and railways lines to the bridge, building sheds for storage, preparing meals for workers, and so on and on. Many briggers stayed for only a few weeks before moving on, in total a very large number. The only figure commonly stated is that 4,600 men were employed at the height of construction.

It is a myth that painting the Forth Bridge is continuous. For generations it was said that when the painters finished at one end they immediately restarted at the other end. That has never been true.

Right now the Forth Bridge requires virtually no painting. A major refurbishment project began in 2001. For ten years sections were screened off to allow sandblasting, minor repairs to the steel, and then a special coating applied of virtually impermeable paint (tinted red). No further work is expected for 20 to 25 years.

As a child I was told people threw pennies out of train windows while crossing the Forth Bridge. It was supposed to bring good luck. It was certainly not good luck for those sailing underneath the bridge who could have been killed by any object thrown from above.

Another thing I learned as a child is that the Luftwaffe tried to bomb the bridge during World War II. This is not true. What is true is that, on 16 October, 1939, 12 German bombers tried to bomb ships moored in the Forth, near to the Rosyth Naval Dockyard and thus also close to the Forth Bridge. Ships were damaged and 16 sailors lost their lives. Two enemy planes were brought down by Spitfires. It was the first air raid over Britain during the war, but the bridge was never the target.

In July 2015 the Forth Bridge was made a UNESCO World Heritage Site. It’s the sixth World Heritage Site in Scotland, and now has the same status as the Taj Mahal and the Great Wall of China. Since 1973 the Forth Bridge has also been a Category A listed building.

Currently 190–200 trains per day cross the Forth Bridge, carrying about 3 million passengers each year.

The bridge has been used in films, notably The 39 Steps in both the 1935 and 1959 versions (though it is not mentioned in John Buchan’s book). It has also been used to market soft drinks, anti-corrosive paint, women’s fashions, oatcakes and it has undoubtedly sold tens of millions of postcards. It’s often been the backdrop for any product from Scotland. Last Christmas my son and daughter-in-law, who live in Edinburgh, sent me a card to which was attached a Forth Bridge badge. Great choice.

Today three bridges cross the estuary of the Forth. Alongside the Forth (rail) Bridge stands the Forth Road Bridge, a suspension bridge, which was opened in 1964. Next in line upstream is the Queensferry Crossing, another road bridge, opened in 2017. The Crossing is the longest three-tower, cable-stayed bridge in the world. Each bridge was built in a different century.[8]

Final thought

I believe nothing made with human hands beats what God has made, such as a dramatic sunset, an awesome mountain range, or the intricate design of a snowflake.

But, even so, we must not be blind to the amazing things that amazing people have made. The Bible says ‘God created mankind in his own image … both male and female’ (Genesis 1:27). That doesn’t mean we look like God but does mean at least some of God’s attributes are found in us. Those include creativity, precision, a sense of what is literally wonder-full.

The Forth Bridge has always filled me with wonder, and the more I’ve looked into its design and engineering the more I’m amazed by the creativity and carefulness of those who imagined and those who built that bridge. I’d be impressed if they’d done it with all the toys of modern technology; they did it without even a calculator.

Not everything we make is good, but many things are. Let’s be grateful for the gifts, the learning, the hard work that people have put in to make these things special.

Andrew Shiva / Wikipedia / CC BY-SA 4.0
**A magnificent 2016 photo of the Forth Bridge, looking downstream (east) towards the North Sea. The built-up area in the upper right is a small part of Edinburgh.**

This three-part story of the Forth Bridge is over. First, thank you for your patience, Each part has been at least 50% longer than most blogs (this one even more than that – sorry!). Second, I’m far from being at my best with technical things, so if I’ve got details wrong, please forgive. Third, more normal blogs will be written from now on – in other words, ‘normal service will be resumed as soon as possible’.

——————————

[1] https://en.wikipedia.org/wiki/Decompression_sickness

[2] https://en.wikipedia.org/wiki/Eads_Bridge

[3] https://www.bigrentz.com/blog/types-of-bridges

[4] Because this illustration (and the next) are side profiles, they show only the pillars on the near side of the bridge. Each has a corresponding pillar on the far side, what will be eventually the other side of the railway track. That’ll be more obvious in later photographs.

[5] https://www.bigrentz.com/blog/types-of-bridges

[6] https://en.wikipedia.org/wiki/Forth_Bridge#Accidents_and_deaths

[7] The first time any street in the world was lit by electricity was in 1878 (in Newcastle), only eight years before superstructure work on the bridge began.

[8] I recommend this site for beautiful photos of the three bridges over the Forth: https://www.scotland.org/about-scotland/scotlands-stories/the-bridges

And there is an excellent short video (approx. 7½ minutes) showing construction and features of the three bridges over the River Forth: https://www.youtube.com/watch?v=tgeFKVX2C-o

The Forth Bridge… deceit, disaster and design

It’s 1853, three years after Thomas Bouch launched his ‘floating railway’ over the Firth of Forth. But – though trains are now being ferried over the river – Bouch is disappointed and frustrated.

Why is he dissatisfied? There are fundamentally two reasons.

First, ferrying trains is not a great solution. Certainly Bouch’s employers in the Edinburgh and Northern Railway are happy – they’ve launched a similar ferry to cross the other east coast estuary of the River Tay. But the ferries carry only a train, not its carriages. That makes everything awkward. Here’s what happens for a train leaving Edinburgh and going north:

– leaves its first carriages on the south shore of the Forth

– gains its second carriages on the north shore of the Forth

– leaves its second carriages on the south shore of the Tay

– gains its third carriages on the north shore of the Tay.

Only after all that does the train have an uninterrupted journey north to Aberdeen. All the transitions before that are time-consuming and logistically complicated.

Second, ferrying is also a horrible experience for passengers. Think how the journey just described is for them. Trains are unheated so they arrive at the Forth already chilled, stand on a pier as the wind whips off the water, clamber on board a ferry which has no shelter for passengers, so they huddle beside the train or boxes or carts while the ferry sails through rough seas. Then they do it all again when they get to the Tay. They’re frozen, miserable and frightened. They’ve occupied three different sets of carriages, walked down or up four piers, and stood on open decks across two wide estuaries. No-one thinks this is a good experience.

Bouch agrees. There’s a centuries-old saying that you can’t make a silk purse out of a sow’s ear – if something is fundamentally bad you’ll never make it wonderful, no matter what you do. His ferries are better than nothing, but they’ll never be a good solution to crossing the east coast of Scotland estuaries.

Bouch is also frustrated. His goal and his passion is to build bridges over the rivers Forth and Tay, not organise a ferry service. Bouch had a self-confidence which some would consider arrogance. And a boldness many would think reckless. That’s before mentioning his super-abundance of ambition and determination.

Rather than sticking to a diet of dissatisfaction, in 1853 he informs his employers, now called the Edinburgh, Perth and Dundee Railways Company, that he wants to build a bridge over the Tay. They don’t take long to answer him. Bouch gets a near-instantaneous ‘no’, and he’s told his idea is insane. Bouch is not in the least happy with that response. Soon after he resigns and establishes his own consultancy firm.

The next few years saw two trends among rail companies: the amalgamation of firms and fierce competitiveness between them to establish the best route north. Then Bouch’s old company was consumed by the North British Railways Company, and Bouch believed new leadership meant new opportunity. He knew the company was desperate to improve the northern route, so in 1860 he approached the North British directors promising he could build bridges over both the Forth and the Tay.

This time Bouch is not rebuffed. It’s a new and more optimistic age, and Bouch leaves with a commission to put his plans on paper.

For the Firth of Forth Bouch planned a lattice-girder bridge. Gardeners know about training plants up a wooden or plastic lattice structure. A lattice bridge is fundamentally the same, a criss-crossed web design, strong and resistant to bending. Perhaps the most famous lattice structure is the Eiffel Tower in Paris.

Bouch’s design was not a problem, but his proposed location was. The river between North and South Queensferry was too deep, so Bouch planned to build his bridge five miles upstream where it was shallower. However, there was a problem. Yes, the depth from surface to river bed was shallower, but below that river bed was more than 200 feet (61 metres) of mud. Mud could not support the piers of a bridge.

Or could it?

At the end of the last blog, I asked if there was ever a serious proposal for bridge supports simply to float in the river. Bouch’s proposal was almost that.

Bouch wouldn’t be stopped by 200 feet of mud on the river bed. He pressed forward with a plan for a two-mile bridge held up by 61 stone piers. Those piers would not sit on rock but on mud. His logic was like this: think of walking on wet sand – your footprints press down but they don’t keep sinking because the sand compresses and holds you up. Bouch’s piers would so compress the mud that the piers would sit – or float – firmly in place.

Convinced? Bouch was, but many were not. Not for a bridge set in a tidal estuary where the water was never still, and, on stormy days, would experience turbulence above and below the surface. An official enquiry studied his plans, and asked hard questions. But Bouch stood firm, showed great confidence, and argued his bridge would stand strong. Remarkably Bouch was given a ‘green light’ and in 1866 a beginning was made.

Work started in June and in August it was stopped. Because of new concern about the design? No – it stopped because of financial deceit. For some time the accounts of the North British Railway Company had been falsified to show profits which never existed. The books had been misrepresented, well and truly cooked, and the company was actually in serious financial trouble. Shareholders were up in arms. One day company directors turned up at the Forth, ordered that work stop immediately, and the builders’ employment was terminated with immediate effect.

Once more Bouch was thwarted. He was about to bridge the Forth, and suddenly he wasn’t. The disappointment was enormous.

However, Bouch was Bouch. Though he was down, he was certainly not out.

In the last blog, I also said we’d find out why Thomas Bouch was hired and then fired. That story comes next.

The action now moves 40 miles north, to the River Tay.

The North British Railway Company is being revived under a new chairman, John Stirling. In 1864, with Bouch at his side, Stirling asks officials in Dundee to provide financial support for a bridge over the Firth of Tay. They agree, and work begins in 1871. (I told the story of the Tay Bridge in an earlier blog. You can find it among those posted here: https://occasionallywise.com/2021/10/).

Bouch was not only responsible for the design of the Tay Bridge, but for its manufacture, construction, and maintenance. Everything was under his control.

But the work at the Tay did not get Bouch’s sole attention. By 1873 he had a new design for a bridge over the Forth. This bridge could be built over the deep water between North and South Queensferry because it would be a suspension bridge, with one of its towers securely anchored on Inchgarvie island, approximately half way across the river. (There is a map showing Inchgarvie island in my last blog.) The towers of the bridge would be 600 feet (183 metres) high, with 1600 foot (488 metre) spans in either direction from the centre tower. Steel chains would hold two railway tracks.

Design of Bouch’s suspension bridge.
*Attrib: Wilhelm Westhofen, Public domain, via Wikimedia Commons*

But there was new concern about this design, this time not about the foundations but the ability of the bridge to withstand wind pressure. Experts gave cautious support, but they would not say this was the best possible design. Despite the concerns, the official Act permitting construction was passed in 1873, and a consortium of railway companies formed The Forth Bridge Railway Company to build the bridge.

At first nothing happened. For one thing there was insufficient money to build. For another, the attention of the North British company was on the Tay Bridge’s construction. No work took place at the Forth until September 1878 (four months after the official opening of the Tay Bridge). Mrs Bouch laid a foundation stone, and by the next spring brickwork appeared on the western edge of Inchgarvie (and can still be seen today).

And not much more was ever done. On a late December evening in 1879 an immense gale blew through the Tay estuary. The northern-bound evening train made its way on to the Tay Bridge. As it passed through the central high girders the pressure against the bridge and the train collapsed that whole section, and every person on the train, some 75 people, perished in the waters of the Tay. What happened that night has been known around the world as the Tay Bridge disaster.

An official Court of Enquiry into the disaster began work just six days later, and took only a few months to present its report. The cause, they wrote, ‘was the pressure of the wind, acting upon a structure badly built, and badly maintained.’ Later they concluded, ‘For these defects both in the design, the construction, and the maintenance, Sir Thomas Bouch is, in our opinion, mainly to blame. For the faults of design he is entirely responsible.’[1]

Bouch disagreed with the Enquiry’s findings but, fairly or unfairly, his opinion didn’t matter. He was disgraced as a bridge designer and builder. A broken man, Bouch became a recluse, and died of ‘stress’ in October 1880. He was just 58.

Some work had continued at the Forth before the Tay Bridge Court of Enquiry report was issued. But now public opinion turned against Bouch, and pressurised The Forth Bridge Railway Company to abandon Bouch’s suspension bridge design. The majority view of public and press became one of doubt that any bridge over either estuary could be safe. All work at the Forth stopped in January 1881, and an Act of Abandonment began its passage through Parliament.

But the case for a bridge was still compelling – not least because rail companies stood to make great profits. If Bouch’s bridge could never be built, then a different design from a respected engineer might succeed. The railway companies asked engineers who knew Bouch’s plans, and knew the challenges of bridging the Forth, to consider options. One of these experts was John Fowler, who, with his partner, Benjamin Baker, had built bridges across the Severn estuary (which divides the west of England from south Wales). These highly qualified engineers believed a bridge at the Forth could be done. With no time to lose, financial and legal steps were taken, and the Abandonment Bill was withdrawn before it could finally pass and become law.

Work on the previous bridge had ended in January 1881 and Fowler and Baker laid a new plan before railway companies less than nine months later. It took only two hours for the companies to accept their proposals, and work began on preparing a new Parliamentary Bill. That Bill passed easily because the engineers were highly regarded and government inspectors validated their plans. The Bill went through all its stages and was given Royal Assent on 12^th July, 1882. At last there was a realistic design.

The original (above) and final design for the Forth Bridge.
*Attrib: Wilhelm Westhofen, Public domain, via Wikimedia Commons*

**John Fowler, Consulting Engineer**
*Attrib: Lock & Whitfield (?)., CC BY 4.0 <https://creativecommons.org/licenses/by/4.0>, via Wikimedia Commons*

But there was still widespread fear whether any bridge over the Forth could be safe. Therefore approval came with many stipulations about its strength, and included rules requiring inspection of construction work by the Board of Trade four times a year. The completed bridge had to be secure, but the incomplete structure must be equally secure at every stage. Parliament specified that this must be the biggest, strongest and stiffest bridge in the world. It must have maximum rigidity downwards under the weight of trains and sideways to withstand wind pressure. Only the best of materials should be used. In addition, the Admiralty required that a bridge must not restrict shipping (the Rosyth naval dockyard lies only a short distance upstream). Murray, in his book The Forth Railway Bridge, writes: ‘The concern and caution of the engineers, combined with these restrictions resulted in the finished installation being at least twice as secure as it needed to be’.[2] (As I wrote before, I’m happy to acknowledge the help Murray’s book has been in providing detail not available elsewhere.)

**Benjamin Baker, designer**
*Unknown author, Public domain, via Wikimedia Commons*

In the end three men were crucial for the design and construction of the Forth Bridge. The two designers have already been mentioned: Benjamin Baker, the designer, and John Fowler, the consulting engineer. The third would be responsible for actually building the bridge. His name was William Arrol, a construction engineer. His business base was only 40 miles away in Glasgow.[3] All three of these men were knighted shortly after the Forth Bridge opened.[4]

**William Arrol, Building contractor**
*Attrib: Wilhelm Westhofen, Public domain, via Wikimedia Commons*

The design Fowler and Baker presented was for a three tower cantilever-truss bridge. More on what those terms mean next time. As well as drawings, they presented a 13 foot (almost 4 metre) model of the bridge to Parliament. All those who found construction drawings hard to follow – the vast majority – were entranced by the model. It was soon put on show to the public.

Today, since the Forth Bridge has stood strong for more than 130 years, it seems strange that opinion was divided on whether this bridge would last. Even the Astronomer Royal wrote to The Times newspaper asserting a gale less than had blown down the Tay Bridge might destroy this Forth Bridge. Spectators stood in lines to see the bridge model, and Fowler and Baker were constantly interviewed about its safety.

Finally Fowler and Baker had a photo taken to illustrate the stability of a cantilever design. Two men (many suppose they were Fowler and Baker themselves) sat on chairs, with arms extended supporting a plank on which sat Kaichi Watanabe, a Japanese apprentice of the firm. Behind them was an illustration of the bridge. As well as their arms they used broomsticks. The men represented the bridge towers, and piles of bricks represented the far ends of the bridge. Kaichi’s weight created compression, with every part of the arrangement supporting the rest. It was all stable.[5] Fowler and Baker were not just engineering experts but superb publicists. The photograph was published in newspapers around the world, convincing many about the bridge’s stability. The photo still features on postcards today.

I’ll stop here. The design work is done and approved, and the next blog will cover the remarkable story of the bridge’s construction.

Before finishing, three things have stood out for me from what’s been covered this time.

First, because someone is sure they’re right doesn’t prove they are. I have some sympathy for Thomas Bouch. He was a visionary who never stopped trying. But I suspect he was also too great a salesman, persuading people his ideas were sound when, very possibly, they had doubts. Did they really believe a bridge resting on mud was a great idea? I suspect not. Corrupt finances halted that plan but Bouch returned later with a different design. Why not the original? Might he have always been uncertain about a bridge resting on a bed of mud? Yet he’d persuaded everyone to let him build it just seven years earlier. A great salesman can sell a bad idea. Wisdom lies in recognising what’s bad and refusing it.

Second, the futures we envisage can suddenly change. Bouch had a bridge complete and operating over the Tay, and another just beginning across the Forth. Surely disappointments were all in the past? Then the Tay Bridge collapsed, he was discredited and all he had done and all he might one day do was changed. He never recovered. For others – especially Fowler, Baker and Arrol – the day of opportunity suddenly dawned, and their names have gone down in bridge-building history for their work on the Forth Bridge. There’s no place for either uncertain optimism or uncertain pessimism about the future.

Third, getting the brilliant best pays off in the long-run. The Forth Bridge met all the conditions laid down for it. It’s a marvel of design and construction. Recent inspections have shown it’s still in excellent condition. I’ve detailed many earlier attempts to bridge the Firth of Forth. None were built. The best was worth waiting for, the Forth Bridge.

Lastly, there are points I raised last week which are not yet addressed:

The surprising reason so many construction workers died.
When painters reached the bridge end, they began painting again at the beginning – true or false?

We’ll get to those. But here’s one more:

How did men work under water (without diving suits of any kind) building the piers on which the bridge rests?

I’m learning a lot, and I hope you are too. More to come.

[1] The official report can be found at: https://www.railwaysarchive.co.uk/documents/BoT_TayInquiry1880.pdf The extracts quoted are from pages 41, 44.

[2] Murray, A. (1983/1988) The Forth Railway Bridge A Celebration, Mainstream Publishing Company, Edinburgh.

[3] Arrol’s business was eventually called Sir William Arrol & Co., and among its many other major construction projects are these: the replacement Tay Rail Bridge (1887), Tower Bridge in London (1894), Forth Road Bridge (1964), Severn Bridge (1966).

[4] Further fascinating information about these three men can be found here: https://www.theforthbridges.org/forth-bridge/history/the-bridge-builders

[5] Knowing little about engineering, I may have explained Fowler and Baker’s illustration poorly. It was, thankfully, sufficiently convincing to the public of their day.

The Forth Bridge … beginnings

A tourist was told he must see the Forth Bridge. ‘Of course,’ he replies, ‘but where are the other three bridges?’ That’s an old joke which rests on the tourist only hearing the bridge name and not knowing the spelling is Forth, not fourth, or that the bridge in question is over the Firth of Forth[1] in east central Scotland near Edinburgh.

The Forth Bridge is only 30 miles from where I grew up. I was young when my parents took me almost underneath the bridge, down by the river where the ferry took car and foot passengers from North Queensferry across to South Queensferry. I hardly remember the ferry, but the memory has remained of the giant bridge towering over me, carrying trains high in the sky.

When I refer to the Forth Bridge, I’m using its proper name. But for some 60 years it has been commonly referred to as the Forth Rail Bridge to distinguish it from the nearby Forth Road Bridge and from the recently constructed Queensferry Crossing, a second road bridge. All three bridges impress me, but it’s the Victorian-era rail bridge that has always taken my breath away.

I’m hoping my excitement and fascination about that bridge is contagious. At the end of October 2021 I wrote a blog about the Tay Bridge and its disastrous collapse during a storm. Around 75 lives were lost. (You’ll find it here: https://occasionallywise.com/2021/10/). Many people have read that blog, including a surprising number in America. I hope this bridge story also captures interest. There’s no collapse to describe though, tragically, more died building the Forth Bridge than were lost when the Tay Bridge fell into the river.

The Tay Bridge and Forth Bridge both straddle estuaries, and they have a shared geographic connection. The Tay Bridge goes north from the county of Fife towards Dundee and the Forth Bridge goes south towards Edinburgh. As a Fifer, I like the idea that my county is at the centre.

The Forth Bridge stands where it does because it almost couldn’t have been anywhere else. The maps explain. The first one shows east central Scotland. Fife is the county in the middle – it looks like a Scottie Dog facing right. At the top of Fife lies the estuary of the River Tay. The Tay Bridge was constructed where the river narrows just south of Dundee.

Look to the southern edge of Fife and you see the much wider estuary of the Forth with Edinburgh just below it. What train companies wanted was an uninterrupted route north passing through Edinburgh and Dundee. Where could a bridge be constructed over the Forth? Most of the eastern part of the estuary was too wide. To the west the river narrows the further you go upstream, but building a bridge there would be a major diversion from a straight route up the east coast of Scotland. There was just one place near the mouth of the Firth where the land to the south and north jutted out, exactly where the two Queensferry villages were located.

That point is the focus of the close-up map below. The river narrows just south of Dunfermline and Inverkeithing, which is why most ferries crossed there. That part of the river had another advantage – a small island halfway across. It’s hard to make out, but an outcrop of rock pokes its head just above the water at the midpoint. That’s Inchgarvie Island which will be a significant secure base for the central tower of the Forth Bridge.

But, our story begins not just hundreds but thousands of years earlier. In this blog I’ll focus on events before the Forth Bridge was even designed.

As we begin, let me commend Anthony Murray’s book The Forth Railway Bridge,[2] one of the most valuable sources of information for me. (I suspect the book is out of print, but there are second hand copies for sale.)

The era of boats

The first crossings of the Firth of Forth happened in ancient times before history was recorded. Small boats are fragile, and the Forth estuary was no stranger to strong tides and fierce winds, so those voyages were hazardous. Yet, the people who lived by the sea or large rivers weren’t fools. They knew when to cross.

Ferry crossings also began millennia ago. Ferries would be slightly larger vessels, likely capable of carrying several people plus cows and horses. They increased in importance when Dunfermline, located just north of the river, became the ancient Scottish capital. Margaret, an English princess, married King Malcolm III of Scotland in 1070. Queen Margaret (later Saint Margaret) was a pious Christian and apparently a good influence on her husband. She became noted for her charitable works, and part of her charity was to properly establish a ferry across the Firth of Forth so pilgrims could travel more easily to St Andrews (in the north east of Fife). The ferry became known as the Queens Ferry and the villages between which the ferry crossed were called North Queensferry and South Queensferry. Some 820 years later those two places would mark the ‘ends’ of the Forth Bridge.

One of Margaret’s sons, King David I, put the ferry crossing on a sounder footing, and granted oversight of it to monks in Dunfermline. During medieval times the ferry was a profitable enterprise. In 1589 James VI (later James I of England) gave the ferry rights to his bride as a wedding present. Early in the 1600s, the ferry passage was divided between 16 feudal superiors. They didn’t operate the ferries, but raked in their share of considerable profits.

The ferrymen appear to have been rough characters, seeing off rivals trying to steal business, lacking civility to customers, and having punch-ups among themselves. In 1637 two ferrymen were fined five pounds each for fighting. That was a substantial fine but each had to pay his five pounds fine to the other, so neither won nor lost. What may have bothered the men more was an order that required them to be friends and drink together.

An oddity for us, but not for those times, was that ferry fares were charged according to the status of the passenger, ranging from three shillings and four pence for a duke, earl or viscount, down to one penny for a humble man or woman. Ordinary folk were cheaper than some animals. A horse, cow, or ox was two pennies, but 20 sheep just four pennies. Everyone and everything had its value, with a simple citizen half the price of a cow. Clearly a boatload of aristocracy was the ferryman’s dream cargo.

The ferry service was much criticised: ferries not in good condition; landing places inconvenient and dangerous; piers scarce; services irregular, and impossible when wind and tide unfavourable; no oversight of the system; ferrymen unpleasant. It was also difficult to access the shores to catch a ferry – transport was bad on the Edinburgh side and nearly non-existent on the Fife side. No airport buses departing every 15 minutes in those days.

Despite the problems, by the early 19^th century ferry traffic was increasing. That stirred a demand for change. So a Board of Trustees was set up to consider what could be done. It reported that the private individuals running the ferries were not likely to take account of public convenience to the extent now required, and recommended nationalising the ferry service. The proposal was fiercely resisted by those who owned the ferries – they called it ‘a violent invasion of private property’ – but the Bill to nationalise the service was passed in 1809.

New ways to cross the river

The increased traffic, and inadequacy of the ferries, stirred ideas for other ways to cross the Forth. This was the early 1800s, close to the Age of Enlightenment, and several more-or-less enlightened ideas were put forward.

One radical proposal came from a group of Edinburgh engineers – they would tunnel under the river. They knew of a London tunnel project under the Thames, and of a mining tunnel under the Firth of Forth at Bo-ness (about 10 miles upstream) which had gone a mile out under the river without difficulty. Led by John Grieve, three engineers surveyed the bed of the Forth at Queensferry and concluded a tunnel was very possible.

But there were challenges other tunnel projects had not faced: the great depth of the water between North and South Queensferry, and the type of rock under the river bed. Both of these factors would make tunnelling difficult. They were forced to modify the route the tunnel would take, but that meant the southerly entrance would be close to Hopetoun House, considered one of Scotland’s finest stately homes with 6,500 acres of grounds. The owner, the Earl of Hopetoun, strongly objected. Grieve pressed on as best he could and drew up plans for a £160,000 project:

It would take four years to construct
There would be two separate tunnels, described by Grieve as ‘one for comers; one for goers’
Each passage would be 15 feet high and 15 feet wide (15 ft = approx 4.5 metres)
There would be a raised sidewalk for pedestrians

Grieve issued a prospectus and shares were offered at £100 each. It got little interest. He tried again the following year, but with no greater success. The scheme collapsed. Grieve was disappointed. The Earl of Hopetoun was delighted.

A quick aside: the idea of a tunnel under the Firth of Forth was revived in 1955. A Forth Road Bridge Joint Board had been set up to plan and oversee the building of a road bridge. But first the Board considered drilling a tunnel under the estuary close to the rail bridge. But, like Grieve’s proposal, after research the idea was abandoned as being too ambitious and too expensive.

Back to our main story. Between 1808 and 1817 new piers were built on both shores. These were ramped piers (sloping down into the water), allowing ferries to dock whether the tide was high or low. They were so well constructed they handled ferry traffic until 1964. It stopped then only because the Forth Road Bridge was opened, and the ferries were consigned to history.

New piers made a big difference to the ferry service, but ferries could never satisfy 19^th century transport needs. This was an era of growth and innovation. Engineering flourished, new roads were built, and bridges constructed where previously they were thought impossible. Imaginative and impressive engineering projects were being developed across Scotland, and all around the world.

An Edinburgh civil engineer, John Anderson, was excited by giant wooden bridges built in China. One bridge was reported to be three miles long. Anderson’s idea was not for a wooden bridge across the Forth, but a suspension bridge so extraordinary it would be one of the wonders of the world. His favoured site was where the ferries crossed. That was the most obvious location, partly because the river at that point was narrow, and because of the small island, Inchgarvie (as explained earlier) The name Inchgarvie is Gaelic and means ‘rough island’. That’s what it is, a small island of solid rock. However, it’s not as modest as it appears, because (like an iceberg) it’s bigger below sea level than above it. Inchgarvie was barren rock but perfect for supporting the centre of a large bridge. The pillars and columns of Anderson’s bridge would be made of cast iron, and coated in linseed oil when hot to ward off rusting. The roadway would be sufficiently wide to allow two-way traffic plus pedestrians. It would be suspended by chains either 90 or 110 feet above sea level, and could be no lower as ships with tall masts had to pass underneath.

Anderson wanted his bridge to be a thing of great artistic merit. He wanted it to look very light so he would use as little iron as possible to reduce the bridge’s weight and mass. With dry humour one later writer said the bridge would indeed have looked very light and slender, almost invisible on a dull day, ‘and after a severe gale it might been no longer seen, even on a clear day’. Anderson’s imaginative but unrealistic design won no support and the plan for a near invisible bridge became exactly that: invisible.

Other developments during the 19^th century were significant for the eventual construction of the Forth Bridge.

Travel by train. The first purpose built railway, a line between Liverpool and Manchester, was authorised in 1826 and opened in 1830. It was a success from the start, beating other forms of transport on time and cost. Road transport was slow and expensive. Canals were used between Liverpool and Manchester but the journey time by rail was one and three quarter hours compared to 20 hours by canal, and the charge for carriage by rail was half the cost of carriage by canal barge. From the start trains were used by the Post Office and soon after for newspaper circulation around the country.

The expansion of railways lines was fast. In 1836, 378 miles of track were open. Eight years later that number had risen to 2210 miles and soon many more. Railways changed society. People moved out of cities because they could now commute to work. Seaside resorts were developed because they could now be reached. Businesses sent their goods throughout the nation, because transport was affordable and fast. In today’s jargon, trains were a breakthrough or disruptive technology.

Because of these economic and convenience benefits of rail travel, it was no longer realistic to think a bridge over the Firth of Forth should be designed for horses, carts and pedestrians. It must carry trains.

Oddly, though, before any bridge was built trains were already crossing the Forth estuary. They floated over.

In 1849 a young man called Thomas Bouch was appointed manager and chief engineer of the Edinburgh and Northern railway and tasked with developing travel up the east coast of Scotland. But Bouch faced two immense problems – the wide estuaries of the Tay and Forth rivers. To make a lengthy journey north or south you could take a train close to an estuary shore. Then goods and people had to detrain, board a ferry, travel through Fife by road or train, get on another ferry, and finally board another train to complete the journey. East coast travel could never prosper while those difficulties existed.

Bouch’s ambition was to build bridges, but he needed a quick fix. His initial solution for crossing the Firth of Forth was what he called a ‘floating railway’ – steam ships big enough and strong enough to carry a train. His first ferry was named ‘Leviathan’, which had proved its seaworthiness because it was built in shipyards on Scotland’s west coast, then sailed north, across the top of Scotland where wind and waves were anything but friendly, and back down the east coast to the Firth of Forth.[3]

Bouch had wasted no time. Within two years of his appointment, his train-carrying ferries began. There were already rail lines running to Granton, near Edinburgh, on the south coast of the Forth, and from Burntisland in Fife on the north coast, so the train-carrying ferries sailed between those two places. It worked, and the floating railway operated for several decades.

But Bouch’s ferries could not be a long-term solution. They had limited capacity, limited frequency, and limited convenience. The demand was for rapid and comfortable train transport, and the answer did not lie with ferries.

A bridge had to be built. And at exactly that time another major development made a large, strong bridge over the Forth a better prospect than ever before.

Reliable steel. Well into the 19^th century, iron dominated the building world. It came in two forms:

Wrought iron – wrought is a past participle of work, so wrought iron is ‘worked iron’
Cast iron – iron shaped by a casting process.

Each has advantages and disadvantages.

Wrought iron is pliable when heated and reheated, so can be bent into any desired shape. It gets stronger the more it’s worked, is not prone to fatigue, and can suffer a lot of deformation before it fails. It’s been used since about 2000 BC.

Cast iron is not pure iron; it contains small elements of carbon, silicon, manganese, perhaps traces of sulphur and phosphorus. The elements are heated beyond melting point, then poured into moulds which give the cast iron its shape. It’s very hard but also brittle. When stressed it’ll break before it bends.

The advantage of cast iron is suitability for complex shapes – think of the decorative metal back to a garden seat – which would take enormous time for a blacksmith to create. But, though strong, cast iron won’t bend when pressure is put on it, and may possibly collapse.

Many buildings and bridges were built with iron. But they had limits. Several bridges collapsed because their underpinnings were cast iron.

Around the mid 1850s, Sir Henry Bessemer developed manufacturing processes to create quality steel which could be used economically in construction. He intended his work to be used for weapons, but it had wider applications. The Bessemer process is described this way: it ‘involved using oxygen in air blown through molten pig iron to burn off the impurities and thus create steel’.[4] It was revolutionary.

This new steel was sufficiently strong, resilient and economic for the grandest and greatest of engineering projects. It didn’t become used widely until about 1880, but that was exactly when it was needed for the Forth Bridge.

It was now time for a serious approach to a bridge over the Forth. The ‘beginnings’ of this story are, therefore, at an end. It’s where we pause, but the story will continue in the next blog.

Already there are lessons we can learn, including these:

During the early years there were people who believed a bridge spanning the Firth of Forth could never be built. They were wrong.
The first bridge concepts were too small and too fragile to meet the need, although understandable given the technology of the time.
New developments created a need and an opportunity. The creation and expansion of train services were the need. The upgrading of steel to major construction quality was the opportunity.
Eventually the time came to act. An age had dawned which demanded bold innovators. Those innovators emerged, and their work was and is magnificent. After more than 130 years the Forth Bridge still fulfils its purpose perfectly.

These four points make me ask these questions. What is there I could be doing but my vision is too small? Beyond me, what are the challenges of this age that need great innovators, and a population willing to adapt, so dangers like viruses, inequality, racism, and climate change can be challenged? This is not a time for saying ‘That could never be done’. It’s the time when something must be done.

Thank you for persevering through a long blog. As the story progresses, we’ll find out:

Was there a serious proposal for bridge supports simply to float in the river?
A surprising reason so many construction workers died.
Why Thomas Bouch was hired and then fired as bridge designer
When painters reached the bridge end, they began painting again at the beginning – true or false?

And many other important and not-really-important facts. So much more to come.

———————–

[1] ‘Firth’ – often used in Scotland – can refer to a river estuary or an inlet of the sea. The Firth of Forth is both.

[2] Murray, A. (1983/1988) The Forth Railway Bridge A Celebration, Mainstream Publishing Company, Edinburgh.

[3] Some of these details come from an obituary of Thomas Bouch following his death in October 1880.

[4] https://en.wikipedia.org/wiki/Henry_Bessemer

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