36 | NewScientist | 11 September 2010

Ozone monitoringTHE great Ernest Rutherford once remarked that all science is either physics or stamp collecting. While physicists are seekers of the truth who uncover sweeping laws of nature, the rest are mere collectors, who pigeonhole things into categories. But the story of the hole shows that collecting and categorising can have a huge impact.

In the early 1980s, when British research faced government cutbacks, long-term monitoring programmes were under threat. Among them were the measurements of atmospheric ozone at the UK’s Halley research station in Antarctica.

The British Antarctic Survey (BAS) was looking at ways to economise, and axing ozone monitoring seemed unlikely to be a big loss. Then, in May 1985, came a bombshell: Joe Farman, Brian Gardiner and Jonathan Shanklin reported large losses of ozone (Nature, vol 315, p 207). The BAS researchers were still using a 25-year-old instrument to assess the thickness of the ozone layer by measuring ultraviolet radiation penetrating the atmosphere. Until then there had only been anecdotal reports of low values, but a trend was vividly revealed when the team plotted averages of minimum measurements. Farman then worked out some of the chemistry of the hole.

While the Brits were using their old-fashioned instrument, NASA’s Nimbus 7 satellite also produced clear evidence of depletion. But so overwhelming was the flood of data and so unprepared were the Americans for unusually low measurements that, fearing an instrument glitch, it was initially overlooked.

Farman’s unexpected discovery showed for all to see how human activity can harm the atmosphere – in this case with the chemicals used in refrigeration, air conditioning and solvents. Governments agreed on action and today ozone levels are predicted to return to their 1950s levels by about 2080 (Nature, vol 465, p 34). Not a bad outcome for a boring philately project. Roger Highfield

Gyro culture

Imaginary numbers

LOUIS BRENNAN was an Irish-Australian engineer who devised a deeply unlikely form of transport: the gyro car whose two wheels were one in front of the other, like a bicycle (see photo, below). It proved to be a dead end, but it blazed a trail for a transport revolution.

Gyroscopes exploit the principle that a rotating object tends to conserve its angular momentum: once it starts spinning, the wheel of a gyroscope resists any force that tries to change its spin axis. Brennan realised that a gyroscope could keep a monorail upright and in 1903 patented the idea. He demonstrated a scaled-down prototype monorail at a

Royal Society conversazione in London in 1907 and “aroused the amazed interest of the world” by one account. The celebrated author H. G. Wells alluded to the event in his 1908 novel, The War in the Air, and described how the audience was concerned by the idea of a gyro car crossing an abyss on a wire cable: “Suppose the gyroscope stopped!”

Brennan went on to demonstrate a full-scale version in 1909 but, as Wells had suggested, safety fears discouraged its commercialisation. Here, Elmer Sperry enters the story.

Having been working on his own gyroscope technology, he bought Brennan’s patents and went on to found the Sperry Gyroscope Company in Brooklyn, New York, to pursue marine applications including gyrocompasses and ship stabilisers . Today, devices developed by Sperry and others are ubiquitous. Gyrocompasses use the gyroscopic principle to keep the needle pointing north, and gyroscopes are also at the heart of related guidance, steering and stabilisation equipment on warships, oil tankers, missiles and more.

Some see a parallel between the unfounded fears that made

Brennan’s gyro-stabilised vehicles look unlikely and current opposition to some modern technologies. Brennan’s monorail worked on sound principles but people feared that malfunction might cause disaster. Sperry used the same scientific principles but concealed them in the technology so they were not perceived as being risky, according to David Rooney of the Science Museum in London. “Many people still voice Wells’s metaphorical concerns,” he says. “What if the scientists get it wrong? Are we heading for a fall?” Roger Highfield

” Gyroscopes are crucial in the systems used to steer, guide and stabilise today’s ships”

WHEN students encounter imaginary numbers, a common response is: what’s the point? Well, quite a lot as it happens, though it took centuries to discover how much.

An imaginary number is the square root of a negative number. Such numbers have become essential tools in microchip design and in digital compression algorithms: your MP3 player relies on imaginary stuff. Even more fundamental than that, imaginary numbers underpin quantum mechanics, the theory that gave rise to the electronics revolution. Little modern technology would exist without complex numbers – numbers which have both a real and an imaginary component.

In the 16th century, when the Italian mathematician Gerolomo Cardano

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