Paul Johnson

The magic moment when you go under the great Forth Bridge

The magic moment when you go under the great Forth Bridge

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There are times when I think that a great bridge is the noblest work of man. I recently had the thrilling experience of travelling under the famous Forth Rail Bridge on a 52,000-ton ocean liner. I was up on the top deck before 7 a.m. to see this remarkable event, which had to be timed exactly to coincide with the right tide. At high tide the clearance of the bridge is 44 metres, and as the liner’s mainmast is 46 metres, its captain has to come in on mid- or low tide. Even so, the clearance is only a few feet, and the magic moment when the vast ship moves into the steel jaws of the structure is vertiginous; the distortions of perspective make you certain a horrible crunch is bound to occur. The new road bridge, a little further up the Firth, has a higher clearance, but even so the feat of negotiating it without a smash appears impossible. Those are occasions when the navigator must put absolute trust in mathematics, for the purely visual evidence is catastrophic.

The Forth Rail Bridge combines utility, beauty and nerve-tingling sublimity in equal proportions, and for my money is the finest piece of engineering in existence. It is the work of the great Sir Benjamin Baker (1840–1907), though the head of the firm which designed it, Sir John Fowler, gets equal billing in the textbooks. Baker was a Somerset man who received his early training in ironworks and acquired an encyclopaedic knowledge of the powers and limitations of hard metals, indeed of other substances too. His papers in technical journals, such as ‘The Working Stress for Iron and Steel’, ‘On the Strength of Brickwork’, and ‘The Actual Lateral Pressure of Earthwork’ were famous in their day, and his seminal articles ‘Long Span Bridges’ had effects all over the world. His first success was the Grosvenor Road rail bridge which took the route from Victoria Station over the Thames — I think it is the earliest rail bridge of its kind and size anywhere. He was involved in the keywork of London Underground — the Metropolitan (what we used to call the Inner Circle), the District, the City and the Central lines, the last two the first actual tube railways. Baker hit upon the ingenious device by which the line dips between stations to increase traction, an engineering system similar to the principle of entasis in Greek Doric temples or the deliberate falsification of perspective in one of Pieter Saenredam’s magnificent church interiors — all cases where success appears to go against common sense. He was also much involved in the Bakerloo line, indeed in so far as any single engineer created the world’s largest underground network, Baker was the man.

Baker (and his boss Fowler) also helped to modernise Egypt, under the benign rule of Lord Cromer, by designing the great Aswan Dam, which for many decades was the prime example of desert and river control. This dam made the Nile function perfectly for over half a century, and it was not until the vainglorious Colonel Nasser, against our advice, brought in the Russians to construct the notorious High Dam at Aswan that things began to go wrong with the world’s most benevolent river. In my lifetime the climate of Upper Egypt has definitely changed for the worse, and this is one instance when the hand of man — or rather of Soviet engineers, creators of many bad and dangerous dams — is clearly to blame. Among other things, Nasser’s dam means that the large river boats, which used to travel all the way upstream from the Cairo Nilometer to Luxor and Aswan, can no longer make the trip, for there is not enough water in some of the shallower locks. The result is that tourists get a distorted view of Egyptian civilisation, seeing only the New Kingdom stuff (what Osbert Lancaster called ‘Ancient Egyptian Hollywood’) and missing the wonders of the Old Kingdom, except for the Giza pyramids, and the Middle Kingdom. What follies the world tumbles into when sound English advice is disregarded!

If Baker, with his profound knowledge of metal stress, had built the rail bridge over the River Tay, Scotland’s longest river, it would not have collapsed in a storm on 28 December 1879, carrying with it a train and 75 lives. When the Forth Rail Bridge was designed shortly after, he decided to reassure the public about rail safety by creating the maximum visual display of immense steel girders. In achieving this effect, he also created almost accidentally a bridge of immense power and beauty. It is only when you draw this magnificent structure, as I did again last month, that you realise what a subtle and intricate design it is, with the colossal lateral girders, 150 feet high, spread-eagling out, and the width of the base three times that of the summit, so that the criss-cross pattern of sheer steel is extremely complicated, hugely difficult to draw, and produces effects of perspective for which there is no parallel in architecture. This bridge is unique — there’s nothing like it anywhere in the world — and to me it is the perfect image of the majesty of steel. Painted ceaselessly, the new coats being applied as soon as the old ones are completed, the bridge has never been out of service in 115 years, except this summer when it was closed for three days for repairs. I believe it will still be in use in the fourth millennium, for properly protected steel does not decay and the basic structure is designed to last for ever. It is likely, therefore, to prove the most enduring masterpiece of Victorian art.

One reason this bridge is so beautiful is that you can take in its three central arches, its towers and its approaches all at one glance, so that the glamour of the concept is immediately apparent. You can do the same with the Acropolis and the Colosseum and the Pantheon, but not with the Baths of Caracalla or Persepolis. As bridge-spans have got wider and the distance covered more immense, this monocular grasp becomes impossible. Neither of the two Severn bridges, which I see every time I go down to my house in Somerset, can be mastered at one glance, except from a great distance, when the details are invisible. With very long bridges, such as that over the Humber, the towers or central supports become insignificant in relation to the span, thus numbing the effect. Whereas the Golden Gate at San Francisco with its Art Deco piers, and the Sydney Harbour Bridge, are both comprehensible unities so that you can gasp in admiration the first time you see them — a single moment of ecstasy — the new masterpieces of the 21st century are diffuse. You can enjoy them, as with a good motorway, only over time as you travel through them. Thus the Honshu-Shikoku Bridge in Japan (1970–99), the largest civil engineering project in history, cannot be taken in while you are stationary, just like Tiepolo’s immense ceiling in the W