Heavy Weather

    One example of unstoppable weather resulted in the destruction of Tay Bridge. At 7.13 on Sunday the 28th December 1879, a train carrying seventy-five passengers was speeding towards Dundee. After leaving St. Fort, the train was due to cross the bridge, a huge structure carrying a railway track supported on iron pillars. When opened in 1878, the bridge had been considered an enormous engineering achievement; receiving a royal blessing from Queen Victoria. However, that night a huge gale began gusting at an estimated 80 miles an hour. As a train approached the bridge, the structure began to weaken and the middle girders gave way.

    Eye witnesses described the sparks which were flying out of the engine as the train plunged into the river. Steamboats were sent out to search for the survivors but all of the seventy-five passengers had died. By the next day rescue teams were pulling out the first bodies.

    At the time, the tragedy of Tay Bridge was not blamed on the strength of the storm but on bad engineering. The enquiry set up to investigate the catastrophe condemned what they considered poor construction and bad maintenance. The engineer, Sir Thomas Bouch, became the scapegoat.

    However, a recent analysis by Professor Swinfen at Dundee University has suggested that it was the winds gusting at 80 miles per hour which were to blame and not a faulty structure. A girder from the Tay Bridge can now be seen in the Museum of Scotland.

    One positive result to come out of the disaster was a better code of building practice, based on greater research into the measurement of winds. In 1846 the spinning-cup anemometer had been invented. This measured wind speed by the rotation of cups causing a spindle to trigger an electric contact, allowing the number of rotations at a given time to be recorded.

    Though this instrument was invented earlier than the Tay Bridge disaster, the importance of recording wind speed on it became more fully understood. As a result greater funding was pledged for observation from both the Meteorological Society and the Meteorological Council of the Royal Society.

    Wind is the result of the movement of air in horizontal directions. The strength of the wind depends on differences in atmospheric pressure, which can be measured using a barometer. High pressure is usually associated with warm days and low pressure with cold wet weather. As the warmer, lighter air rises, so the cooler heavier air takes its place. As a result wind moves from high pressure areas to low pressure areas.

    The reason why many winds become strong and develop into storms is the result of a centre of low pressure which has large pressure gradients surrounding it. This creates very strong winds that have the potential to destroy the environment in which they develop. On a weather forecast map this is indicated by how close the isobars are. Isobars are made up by joining the points with the same surface pressure.

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