Sherwood Rowland: when good science is not enough

If you want to spur action, you need a disaster - as the case of ozone-destroying CFCs shows.

If you want to spur action, you need a disaster - as the case of ozone-destroying CFCs shows.

After his death on Saturday, much will be written about chemist Sherwood Rowland's triumph in getting chlorofluorocarbons (CFCs) and other ozone-destroying chemicals banned. The truth about Rowland's story is a little less inspiring than the legend, however.

Rowland and his colleague Mario Molina published the first paper on the threat to the ozone layer in June 1974. It took thirteen years before the Montreal Protocol, limiting the industrial production of those chemicals, was finally ratified.

Those were extremely painful years for Rowland. His colleagues shunned him for his activism in support of a ban. Almost no university chemistry departments would have him come and speak for nearly a decade -- unthinkable for a chemist of his calibre. Twelve years passed without him being invited to speak to industry groups. James Lovelock, now practically a saint, thought Rowland was going too far: he called for a "bit of British caution" in the face of Rowland and Molina's "missionary" zeal for a ban on CFCs.

If the science establishment doesn't come off too well in that era, Rowland was not without fault either. It may have been in response to pressure from his colleagues, but part of the reason the ban took so long to achieve was that, at a crucial time in the debate, Rowland announced results that cast doubt on the case against CFCs before checking them thoroughly or offering them up for review by others.

In 1976, CFCs' defenders had suggested that the ozone-attacking chemicals might get mopped up by nitrogen in the atmosphere. They would then be rendered safe. Rowland entertained the idea and declared that his estimates of likely ozone depletion by CFCs had been between 20 and 30 percent too pessimistic.

The pronouncement threw the whole issue into confusion at an extremely delicate time. The US National Academy had been about to issue a report into what should be done about CFCs; now they said they needed more time. The Observer declared that the "Aerosol scare 'may be over'". Chaos ensued, and the scientists fell upon each other.

Two months later, Rowland had discovered a mistake in his calculations, but the damage was already done. Because of the confusion, the furore and the persistence of doubts, the National Academy eventually issued its report with significantly weakened conclusions -- so weak in fact, that the following day's New York Times reported the Academy as recommending a curb on aerosols, while the headline of the Washington Post screamed out "Aerosol Ban Opposed by Science Unit".

In the end, it wasn't the carefully-honed arguments of scientists that got CFCs banned. In 1985, scientists announced they had discovered an enormous hole in the ozone layer over the Antarctic. There was a public outcry and the politicians leapt to their feet. The Montreal Protocol was signed two years later. If there's a lesson to be learned from Sherwood Rowland's work, it's that science isn't enough. If you want to spur action, you need a disaster.

In fact, the scientists carried on debating CFCs long after the politicians had moved on. In 1992, five years after Montreal, a group of MIT scientists organised a scientific forum ahead of the environmental summit in Rio de Janeiro. They invited Mario Molina to give a talk. But they scheduled a Brazilian meteorologist to talk first; to Molina's shock, the Brazilian declared to the assembly that the ozone depletion theory was a sham. If there was any depletion, he said, it was due to chlorine from sea spray and volcanoes.

In many ways, the cautious nature of science is its trump card, its ace in the hole. We trust science precisely because it has got things wrong in the past, gives ear to corrective viewpoints and slowly put itself right. But when something is important, we can't wait for all the scientific arguments to be resolved -- because, as the case of Sherwood Rowland shows, that can take longer than any of us can afford.

Michael Brooks's "Free Radicals: the Secret Anarchy of Science" is published by Profile Books (£12.99)

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

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Inside Big Ben: why the world’s most famous clock will soon lose its bong

Every now and then, even the most famous of clocks need a bit of care.

London is soon going to lose one of its most familiar sounds when the world-famous Big Ben falls silent for repairs. The “bonging” chimes that have marked the passing of time for Londoners since 1859 will fall silent for months beginning in 2017 as part of a three-year £29m conservation project.

Of course, “Big Ben” is the nickname of the Great Bell and the bell itself is not in bad shape – even though it does have a huge crack in it.

The bell weighs nearly 14 tonnes and it cracked in 1859 when it was first bonged with a hammer that was way too heavy.

The crack was never repaired. Instead the bell was rotated one eighth of a turn and a lighter (200kg) hammer was installed. The cracked bell has a characteristic sound which we have all grown to love.

Big Ben strikes. UK Parliament.

Instead, it is the Elizabeth Tower (1859) and the clock mechanism (1854), designed by Denison and Airy, that need attention.

Any building or machine needs regular maintenance – we paint our doors and windows when they need it and we repair or replace our cars quite routinely. It is convenient to choose a day when we’re out of the house to paint the doors, or when we don’t need the car to repair the brakes. But a clock just doesn’t stop – especially not a clock as iconic as the Great Clock at the Palace of Westminster.

Repairs to the tower are long overdue. There is corrosion damage to the cast iron roof and to the belfry structure which keeps the bells in place. There is water damage to the masonry and condensation problems will be addressed, too. There are plumbing and electrical works to be done for a lift to be installed in one of the ventilation shafts, toilet facilities and the fitting of low-energy lighting.

Marvel of engineering

The clock mechanism itself is remarkable. In its 162-year history it has only had one major breakdown. In 1976 the speed regulator for the chimes broke and the mechanism sped up to destruction. The resulting damage took months to repair.

The weights that drive the clock are, like the bells and hammers, unimaginably huge. The “drive train” that keeps the pendulum swinging and that turns the hands is driven by a weight of about 100kg. Two other weights that ring the bells are each over a tonne. If any of these weights falls out of control (as in the 1976 incident), they could do a lot of damage.

The pendulum suspension spring is especially critical because it holds up the huge pendulum bob which weighs 321kg. The swinging pendulum releases the “escapement” every two seconds which then turns the hands on the clock’s four faces. If you look very closely, you will see that the minute hand doesn’t move smoothly but it sits still most of the time, only moving on each tick by 1.5cm.

The pendulum swings back and forth 21,600 times a day. That’s nearly 8m times a year, bending the pendulum spring. Like any metal, it has the potential to suffer from fatigue. The pendulum needs to be lifted out of the clock so that the spring can be closely inspected.

The clock derives its remarkable accuracy in part from the temperature compensation which is built into the construction of the pendulum. This was yet another of John Harrison’s genius ideas (you probably know him from longitude fame). He came up with the solution of using metals of differing temperature expansion coefficient so that the pendulum doesn’t change in length as the temperature changes with the seasons.

In the Westminster clock, the pendulum shaft is made of concentric tubes of steel and zinc. A similar construction is described for the clock in Trinity College Cambridge and near perfect temperature compensation can be achieved. But zinc is a ductile metal and the tube deforms with time under the heavy load of the 321kg pendulum bob. This “creeping” will cause the temperature compensation to jam up and become less effective.

So stopping the clock will also be a good opportunity to dismantle the pendulum completely and to check that the zinc tube is sliding freely. This in itself is a few days' work.

What makes it tick

But the truly clever bit of this clock is the escapement. All clocks have one - it’s what makes the clock tick, quite literally. Denison developed his new gravity escapement especially for the Westminster clock. It decouples the driving force of the falling weight from the periodic force that maintains the motion of the pendulum. To this day, the best tower clocks in England use the gravity escapement leading to remarkable accuracy – better even than that of your quartz crystal wrist watch.

In Denison’s gravity escapement, the “tick” is the impact of the “legs” of the escapement colliding with hardened steel seats. Each collision causes microscopic damage which, accumulated over millions of collisions per year, causes wear and tear affecting the accuracy of the clock. It is impossible to inspect the escapement without stopping the clock. Part of the maintenance proposed during this stoppage is a thorough overhaul of the escapement and the other workings of the clock.

The Westminster clock is a remarkable icon for London and for England. For more than 150 years it has reminded us of each hour, tirelessly. That’s what I love about clocks – they seem to carry on without a fuss. But every now and then even the most famous of clocks need a bit of care. After this period of pampering, “Big Ben” ought to be set for another 100 or so years of trouble-free running.

The Conversation

Hugh Hunt is a Reader in Engineering Dynamics and Vibration at the University of Cambridge.

This article was originally published on The Conversation. Read the original article.