Image caption The reputations of engineers and architects are built on the quality of their work

While engineers can be judged almost instantly by the quality of their work, a longer-term view is required when examining the reputations of our politicians, says Lisa Jardine in her Point of View column.

At some point during his final year at university, my eldest son explained to me why he had decided on a career as an engineer, and had never considered following me into an academic life in the humanities.

"The thing is", he said, "when an engineer designs and builds a bridge, he is assessed strictly on the basis of the work he has produced. If the bridge does what it was intended to do, he is a good engineer. If it fails - if, at worst, it falls down - he is a bad one."

"Whereas," he continued, "in your profession, there are no objective criteria for success. However original what you write is, your reputation depends almost entirely on the opinion of others."

In the end my son did not become a civil engineer - he works in semiconductors. But driving across France a couple of weeks ago, I found it easy to understand why he chose bridge-building as his example of a feat of engineering which can stand up to public scrutiny. Whichever route you take southwards, sooner or later you will find yourself gasping in amazement as you speed across a viaduct of almost impossible daring and beauty, suspended between sky and earth, seemingly defying the laws of gravity.

In summer 2005, our slightly circuitous descent to the Mediterranean took us across the newly opened Millau viaduct on the A75 - architect Norman Foster's magnificent recent addition to the French landscape. It had been opened the previous winter with much pomp and ceremony by the then French President Jacques Chirac.

Only days before our own holiday departure in late July the following year, we had been glued to our television as the 18th stage of the 2005 Tour de France took the riders under the new bridge, affording the world of cycling enthusiasts magnificent aerial views of the soaring, elegant, structure, gracefully curving across the Gorge du Tarn, courtesy of the accompanying helicopters.

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That was the year American cyclist Lance Armstrong won the Tour for an unprecedented seventh time. Nevertheless, the Millau viaduct stole some of his thunder as he made his way triumphantly towards Paris to claim the famous final yellow jersey.

I said that the Millau bridge was the work of architect Lord Norman Foster. It is to him that we owe the purity of its minimalist good looks. The delicate cable-stayed structure appears almost transparent, and seems to slice like a sharpened knife-edge through the lush landscape crossing this impossibly wide section of the valley of the Tarn.

But in fact the name that heads the dossier of those responsible is not that of the architect, but of the prize-winning French engineer Michel Virlogeux. Dr Virlogeux is the engineer behind an impressive number of spectacular suspension bridges, including the Vasco da Gama bridge across the Targus river near Lisbon (completed in 1998), which is the longest suspension bridge in Europe.

The construction company responsible for financing and building the Millau viaduct has a particularly distinguished history of involvement with iconic structures on a very grand scale. The Eiffage group was the company responsible for the Eiffel Tower in Paris, designed by the firm's founder, Gustave Eiffel, as the gateway to the Universal Exposition of 1889.

'Wobbly'

Until the construction of the Chrysler Building in New York in 1930, the Eiffel Tower was the tallest man-made structure in the world. Fittingly, perhaps, the tallest pylon of the Millau bridge stands 343 metres tall - 22 metres taller than the Eiffel Tower itself.

Bridge-building on a heroic scale goes deep into French history and culture. It was Napoleon Bonaparte who in 1804 established the Conseil Général des Ponts et Chaussées - the General Council for Bridges and Roads - by imperial decree, to oversee a massive road and bridge-building programme providing proper communications (and military marching routes) from one end of France to the other.

Michel Virlogeux (the man behind the Millau viaduct) was trained and later taught in the highly esteemed Ecole Nationale for bridges and roads - the world's oldest civil engineering school, founded in 1747. In keeping with this very French tradition of treating engineers with special esteem, Gustave Eiffel had the names of 72 great French scientists and engineers inscribed on the frieze below the first balcony of his Eiffel Tower.

Is it really the case that those of us who have to depend on less concrete evidence of our abilities to establish our standing in the world are more vulnerable to having our achievements diminished simply on the whim of others?

We in Britain are rather more suspicious of ambitious public projects of this kind. Norman Foster's name is associated with a bridge of comparable grace and elegance to the Millau Viaduct, the Millennium Bridge in London. It, however, threatened to become dubbed one of those "failures" my son believed could ruin an engineer's reputation for good.

Originally designated the "blade of light" bridge by its design team (which also included the distinguished sculptor Sir Anthony Caro), this lean, improbably low-slung, silvery cable-suspension bridge across the Thames from St Paul's Cathedral to Tate Modern, quickly became known - and is still known to Londoners today - as the "wobbly bridge". On its opening day, as a parade of local schoolchildren marched across it, accompanied by unexpectedly large numbers of onlookers, the bridge began to heave and sway. I know, because I was there. If, like me, you were prone to sea-sickness, you were driven to cling to one of the handrails of the bridge, and edge your way gingerly to safety. The bridge was closed as unsafe after only two days.

During the period of closure, the reputations of those associated with it certainly suffered. The Millennium Bridge was dubbed "Britain's most infamous architectural experiment" and the team responsible for its innovative design was accused of not having anticipated obvious potential risks.

Fortunately, the engineering problem was eventually solved by adding almost 100 discretely placed energy dissipating horizontal dampers and inertial vertical shock-absorbers, and the Millennium Bridge reopened in February 2002. Since then it has become a much-loved London landmark and has enhanced the reputation of its engineers, Ove Arup and Partners.

Apparently, then, reputations are not only made and lost for engineers by the structures they create, they can even be saved by some ingenious and innovative solutions to problems - like wobble - that arise. So is it really the case that those of us who have to depend on less concrete evidence of our abilities to establish our standing in the world are more vulnerable to having our achievements diminished simply on the whim of others?

Shakespeare would certainly have it so. In Othello, Cassio, the Moor's lieutenant, led astray by the malevolent Iago, and caught drunk on duty by his master Othello, bewails the fact that his rash behaviour has permanently deprived him of his position of esteem in the eyes of the world:

Image caption British politicians are careful to be seen to be holidaying frugally

"Reputation, reputation, reputation! O, I have lost my reputation! I have lost the immortal part of myself, and what remains is bestial."

Try as he may, Cassio cannot regain his master's trust, and all his subsequent actions are interpreted by Othello as further evidence of his unreliability. Eventually, of course, Othello is even persuaded by Iago that Cassio has seduced his blameless wife Desdemona.

But if my son thinks those who make a career in the humanities are liable to have their reputation tarnished on the whim of an academic committee or a Sunday supplement book reviewer, he might consider the even worse lot of politicians. For them, reputations are won and lost at a yet faster rate.

Which may explain why our own politicians are currently anxious to secure public approval by their modest choice of holiday destination, in keeping with the new government's austerity measures.

Gone are the photo-opportunities in glamorous villas in Sardinia and Barbados, lent by foreign heads of state or pop stars, the cruises with Russian oligarchs. This summer, we are told, the Camerons are holidaying frugally in Cornwall, while David Miliband and his family have rented a humble cottage in Northumberland. The Cleggs will take a break in Olmedo, just south of the Spanish city of Valladolid, where his wife was born, and which is, according to the deputy prime minister, "totally off the tourist track".

I doubt that such efforts will have much effect. The tide of events may thwart even the best-intentioned efforts of politicians to build lasting reputations. At any moment, a sudden drop in the economic growth-rate is enough to turn public opinion.

Their consolation has to be that in the long view, the verdict of history is more considered, and may yet restore that 'immortality' of reputation to which Shakespeare has Cassio declare such passionate commitment.