by Bill Bryson
The first significant departure from the use of a stiffening truss had occurred in the design and construction of the George Washington Bridge, which opened in 1931 and crosses the Hudson River between New York and New Jersey. The exceptional width of this bridge’s roadway and the consequent weight did make a truss unnecessary in this case, but in regions where light traffic meant that only two lanes were required, a narrow and shallow bridge deck meant also a much lighter and more flexible structure. Suspension bridge designers sought to fit their structures with ever more slender decks. By the end of the 1930s, this trend produced bridges whose roadways moved a suprising amount in the wind. There was no satisfactory theoretical explanation for this behaviour, but engineers felt confident that their bridges were in no danger of collapse.
They were disabused of that in 1940, when the Tacoma Narrows Bridge, whose deck had been undulating in the wind for months, began to twist and soon collapsed. Since the undulations had been occurring for some time, the bridge was the object of an ongoing study. Its misbehaviour was being investigated experimentally through a scale model, and the real bridge was being filmed. On 7 November, when the vertical undulations changed over to torsional oscillations, a film crew was despatched to capture the new behaviour. The twisting lasted for hours, and the final writhing of the steel structure caught on film made the bridge infamous. Indeed, before the collapse of the New York World Trade Center twin towers, the failure of the Tacoma Narrows Bridge was the most widely viewed structural collapse in engineering history.
Today, bridges of unprecedented scale and unchallenged beauty continue to be designed and built worldwide, and they require no less of a team than did their predecessors. The seemingly unrelated aims of functional strength and aesthetic appeal had been not only successfully integrated in many of the classic suspension bridges of the past two centuries but also commonly achieved by engineers alone or leading teams. Thomas Telford was in fact both engineer and architect of his Menai Suspension Bridge, and John Roebling was both engineer and architect of his Brooklyn Bridge. That these engineering structures especially have come to be regarded as architectural icons demonstrates the aesthetic heights that an engineer can achieve.
Engineers less artistically confident than Telford and Roebling have engaged consulting architects to advise them on the design of everything from the façades placed on massive anchorages and skyscraper-high towers to the finishing details like deck railings and lampposts. Othmar Ammann, the chief engineer of the George Washington and many other New York City bridges, often sought the help of famous architects. When the George Washington was but an idea on paper, Ammann engaged Cass Gilbert, the architect of the Woolworth Building and other landmarks, to depict how the towers might be finished in stone. Since money was tight when the bridge was being completed, however, the steel-framed towers were left bare – a look that the Swiss architect Le Corbusier found extremely appealing – and bare steel became the new aesthetic standard for monumental bridge towers. For his Bronx–Whitestone Bridge, Ammann engaged the ‘architect to the elite’ Aymar Embury II in designing the structure’s anchorages. It was Embury’s suggestion that they express the force that they exert against the pull of the suspension cables and show its trajectory into the monolithic bookends of the bridge proper.
But relationships between architects and engineers were generally strained in America in the 1920s and 1930s. There had been continuing tensions over which of these professionals should control bridge projects. The architects argued that they were better prepared to choose the form and site for a bridge, leaving it to engineers working under them to figure out how to build the structure. But, unlike large buildings, long-span bridges had traditionally been sited, designed and constructed under the direction of a chief engineer. The increasing structural challenges presented by long-span bridges kept the engineers in control.
In a series of articles in Civil Engineering magazine, the architect Embury described his working relationship with the engineering team for the Bronx–Whitestone and made it clear that the chief engineer always had the final decision. According to Embury, in a bridge project engineers and architects alike were ‘instruments’ of the one chief engineer and ‘were guided by his desires as to the lines along which we should proceed’. But neither was Embury uncritical of his colleagues in either camp. He did not approve of engineers pursuing ‘design by drawing instruments’, by which he meant that they tended to use certain angles in their structures because they were the ones of the drafting instruments close at hand. He was also critical of his fellow architects, who he felt too often followed ‘the easiest way’. In an attempt to promote a meeting of the minds, Embury believed that ‘engineers should be good architects, and architects good engineers’. Who could argue with that?
In more recent years commissioning organisations have tried to force engineers and architects to be equal partners in bridge design. The design competition guidelines for the Gateshead Millennium Bridge, the strikingly original arch-and-cable ‘blinking-eye’ movable structure that carries pedestrians over the River Tyne between Gateshead and Newcastle, made it clear that multidisciplinary teams were expected to produce entries ‘of sufficiently high technical and aesthetic merit’.
The design competition for the London Millennium Bridge, the low-slung suspension bridge for pedestrians that spans the Thames to tie together St Paul’s Cathedral and the Tate Modern museum, went further than the Gateshead one. For the London crossing, it was required that design teams comprise not only engineers and architects but also artists. The winning entry was a collaboration among the engineering firm of Ove Arup, the architectural firm of Norman Foster and the sculptor Anthony Caro. The resulting long, slender-decked bridge has been described as a ‘blade of light’, which it resembles when viewed from a distance up or down the river. As was the case with the Tacoma Narrows Bridge four decades earlier, aesthetics dominated structure, and the unconventional design of the Thames crossing allowed its deck to move sideways excessively under the crowds of pedestrians that flocked to its opening in June 2000. After three days of movement that was deemed potentially dangerous for people, if not the bridge itself, the structure was closed. Much of the public blame for the fiasco fell on the engineers, who were sent back to the drawing board. After being retrofitted with dampening devices, some of which may be said to compromise its aesthetics, the bridge was reopened and has become a popular tourist attraction.
Artistic designs like the Gateshead and London Millennium bridges may not be suitable for large-span bridges that carry vehicles as well as pedestrians. But that is not to say that such large-scale bridges cannot also have a strikingly innovative aesthetic component. The relatively new bridge form that has become a favourite for achieving striking profiles and dramatic effects is the cable-stayed bridge. In contrast to the suspension bridge, from whose two or four main cables a roadway is hung, the cable-stayed bridge employs multitudes of cables that stretch directly from towers to deck. The great number of cables allows for a wide variety of arrangements, and so each cable-stayed bridge can have a distinctive look. This characteristic has led to the design of unique bridges known as ‘signature bridges’.
Among the most widely admired new bridges of this type is the Millau Viaduct, which carries a very high roadway across the Tarn Valley, formerly a traffic bottleneck on the road between Paris and Barcelona. The Millau is a breathtakingly striking design that is commonly attributed to the architect Norman Foster, and it certainly is an architectural achievement in its sculptural form and the way it harmonises with its dramatic natural setting. However, the structural design and construction of such a towering bridge are not architectural but engineering achievements. Unfortunately, the French bridge engineer Michel Virlogeux, who was responsible for the structural design, is largely forgotten when the bridge is marvelled at.
Architects may be more extroverted and therefore the more visible members of a bridge design team today, but they are not always the most es
sential. Perhaps we ought to revive the grand tradition embodied in John Lucas’ Conference of Engineers to remind us of what was obvious in the nineteenth century, but may now be forgotten.
11 GEORGINA FERRY
X-RAY VISIONS: STRUCTURAL BIOLOGISTS AND SOCIAL ACTION IN THE TWENTIETH CENTURY
Georgina Ferry is a science writer, broadcaster and biographer. She is the author of Dorothy Hodgkin: A Life, The Common Thread: A Story of Science, Politics, Ethics and the Human Genome (with John Sulston), A Computer Called LEO: Lyons Teashops and the World’s First Office Computer, and most recently, Max Perutz and the Secret of Life.
SCIENTISTS NEED TENACITY: NONE MORE SO THAN THOSE WHOSE PAINSTAKING, DRAWN-OUT WORK PICTURED THE THREE-DIMENSIONAL STRUCTURES OF THE VAST MOLECULES BUILT BY LIVING CELLS. AS GEORGINA FERRY RELATES, THE STRENGTH OF CHARACTER DEMANDED BY CRYSTALLOGRAPHY OFTEN WENT ALONG WITH STRONG CONVICTIONS ABOUT THE ROLE OF SCIENCE IN SOCIETY.
Anyone crossing the courtyard of Burlington House in Piccadilly on a certain day in 1945 would have seen a contrasting couple sitting on the steps of the East Wing, then home to the Royal Society. She was slight, girlish, a fair-haired woman in her thirties with penetrating blue eyes. He was a decade older, shock-headed, fleshy-faced and physically imposing. Waiting for a colleague, they were discussing her latest scientific result. Delightedly she confided that after two years of wartime work, still officially a secret, she and her colleagues had solved the structure of penicillin. ‘You’ll get the Nobel Prize for this,’ he said. She countered that she would far rather be elected one of the Fellows on whose doorstep she was sitting. Without irony, he told her ‘That’s more difficult.’ 1
Wrapped up in this anecdote about Dorothy Crowfoot Hodgkin and John Desmond Bernal is a whole chapter of interlocking stories: about collegiality, about scientific workers of both sexes, about the impact of war on research, but above all about the conviction that knowing how biological molecules were constructed from atoms in three dimensions would fundamentally alter our understanding of life. Hodgkin (FRS 1947) and Bernal (FRS 1937), her former PhD supervisor and lifelong mentor, were among the founders of a project that at first seemed hopeless, even quixotic in its ambition: to use physical techniques to reveal the structure of life in atomic detail. Today their inheritors are at work every day, using essentially the same techniques to build a catalogue of the shapes of every molecule in the living body, and applying that information to understand health and disease and to design new drugs.
The legacy of the structure pioneers, however, is richer than the sum of their scientific achievements. Each in his or her own way, they gave their considerable energies to causes such as scientific education, the organisation of research, international understanding, gender equality, human rights, prison reform and world peace. Partly because the subject crossed so many disciplinary boundaries, but also because of the personalities involved, they also developed a way of doing science that valued collaboration over competition, and fostered egalitarianism in relation to rank, gender and class.
FATHER AND SON
Everyone in this story can trace a scientific lineage back to William Henry Bragg (FRS 1907) or his son William Lawrence Bragg (FRS 1921).2
Most would also credit the Braggs with establishing the egalitarian outlook that the early structural biologists shared. William H. Bragg was born in the UK and studied at Cambridge, but in 1885, at the age of twenty-three, he was appointed to the professorship in physics at the University of Adelaide. In 1909 he returned from Australia to take up the chair in physics at Leeds. His nineteen-year-old son Willie immediately went to Cambridge to study natural sciences.
In 1912 the Munich-based physicist Max von Laue and his junior colleagues reported that a zinc sulphide crystal could diffract a beam of X-rays, producing a characteristic pattern of spots on a photographic plate and demonstrating the wave-like nature of X-radiation. Bragg père, who at that time inclined to the view that X-rays consisted of particles, was tipped off about the paper by a colleague who was working in Germany. When Willie came home for the long vacation they pored over the problem, and in subsequent months began their own experiments. Willie confirmed that X-rays formed diffraction patterns on passing through crystals (in the same way that light does on passing through narrow slits), and therefore behaved like waves. He went on to demonstrate that a simple mathematical formula (now known as Bragg’s Law) could relate the positions and intensities of the spots in the pattern to the positions of the parallel layers of atoms in the crystal from which the X-rays were reflected. The formula required a figure for the wavelength of the X-rays, and the Braggs were able to measure this using an X-ray spectrometer of Bragg senior’s invention. Applying the formula to X-ray photographs of simple compounds such as sodium chloride, Willie Bragg was able to draw a picture of the sodium and chlorine atoms neatly alternating throughout the cubic lattice, like the simplest of wallpaper patterns but in three dimensions.
The Braggs had turned X-ray diffraction from an intriguing observation into a tool for exploring what matter is made of in the range that was too small to be seen with a microscope, and too large for chemical analysis. They shared the 1915 Nobel Prize in physics for their discovery. The announcement came when the younger Bragg, aged only twenty-five, was in France developing sound-ranging techniques to help the allies in the war against Germany to fix the coordinates of enemy artillery batteries. He remains the youngest person ever to win a Nobel. Years later Max Perutz summed up the range of discoveries that subsequently flowed from the Braggs’ achievement:
Why water boils at 100°[C] and methane at -161°, why blood is red and grass is green, why diamond is hard and wax is soft, why graphite writes on paper and silk is strong, why glaciers flow and iron gets hard when you hammer it, how muscles contract, how sunlight makes plants grow and how living organisms have been able to evolve into ever more complex forms … The answers to all these problems have come from structural analysis.3
Knighted in 1920, Sir William Bragg moved to London as Professor of Physics at University College (UCL), and then Director of the Davy-Faraday Laboratory at the Royal Institution (RI), a post that he held from 1923 until his death in 1942. A central figure in British science, he was also President of the Royal Society from 1935 until 1940. Long before ‘public understanding of science’ became a topic of debate, Bragg retained the nineteenth-century assumption that new discoveries in science should be part of public discourse, and was an enthusiastic writer and speaker. In 1919 he gave the Christmas Lectures for children at the Royal Institution on the subject ‘Concerning the Nature of Things’; six years later he again fascinated his young audience with his series ‘Old Trades and New Knowledge’. Both series were published as books, and contained some of the first public descriptions of the capacity of X-ray crystallography to open up new perspectives:
The discovery of X-rays has increased the keenness of our vision … a thousand times, and we can now ‘see’ the individual atoms and molecules.4
From the early 1920s Bragg began to use X-ray crystallography to investigate organic molecules (those containing carbon, which include all the molecules that make up living things) rather than the simple, inorganic salts that his son continued to work on as a very young professor at Manchester. Now well into his sixties and with heavy administrative responsibilities at the RI, Sir William recruited young men and women to join his endeavour in the laboratories where Humphry Davy and Michael Faraday had conducted their chemical and electrical experiments a century before.
Bill Astbury (FRS 1940), the son of a potter from Stoke on Trent, had gone to Cambridge on a scholarship and graduated with a First in Natural Sciences. Joining Bragg as a postgraduate at UCL and the RI, he began to use X-ray diffraction to study the structure of natural fibres such as wool that are made of large, complex protein molecules. In 1928 he moved to the University of Leeds, an important centre of the textile industry, where he continued to develop the technique of fibre diffraction. During the 1930s he
was the first to take X-ray photographs of DNA fibres (long before anyone had established its significance as the molecule of heredity). Although he was not able to obtain definitive structures, his insights into the ‘coiled’ nature of these molecules were fundamental to later discoveries by Linus Pauling (the alpha helix of proteins) and Maurice Wilkins, Rosalind Franklin, James Watson and Francis Crick (the DNA double helix).
Kathleen Yardley (later Lonsdale, FRS 1945) was the tenth child of an Irish postmaster who had a drink problem. Her mother brought the family to England for a better life, and in 1922 Yardley graduated from Bedford College (a women’s college of London University) with the highest mark in physics that anyone in the university had achieved for ten years. Bragg immediately wrote to recruit her as his research assistant. When she married fellow researcher Thomas Lonsdale and had three children, Bragg kept her supplied with work she could do at home, then found her a grant to pay for domestic help so that she could come back to the lab. This concern to create conditions in which a married woman could pursue a scientific career was wholly exceptional at the time, as was Thomas Lonsdale’s willingness to share domestic chores and support his wife in her career. Kathleen Lonsdale clarified the structure of a number of small organic molecules, notably confirming that benzene was a flat ring of six carbon atoms, each with a hydrogen attached.
