Sat 19th July 2008
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Types of Barometers - Mercury and Aneroid
Mercury Barometers – the earliest type of barometer.
Most mercury barometers are called ‘stick barometers’ – they consist of a long glass tube with a reservoir or bowl at the base, filled with mercury on a wooden mount with a calibrated scale behind the top of the tube for measuring and recording changes in atmospheric pressure – they are often fitted with a thermometer. The best known mercury barometer is the Admiral Fitzroy Barometer – named after Admiral Fitzroy provider of the world's first weather forecasting service and earlier Captain of H.M.S. Beagle (of Charles Darwin fame).
Aneroid Barometers
Aneroid barometers are usually round or wheel shaped and are either mounted in a circular wooden mount (bracket) or set in a ‘Banjo’ shaped wooden mount. Banjo barometers can be very ornate with inlaid veneers, bevelled glass and brass fittings. You will often find that a banjo barometer is also fitted with a thermometer, a hydrometer (displays the humidity) or a storm gauge.
When fitted in a solid brass case an aneroid barometer is referred to as a marine barometer.
A history of Barometers
Evangelista Torricelli (1608-1647) was a mathematician and physicist with an interest in creating vacuums. In 1641 he moved to Florence, Italy to assist Galileo the great astronomer. Torricelli had been using water in his vacuum experiments and it was Galileo who suggested he try using mercury. Torricelli filled a 4ft glass tube that was sealed at one end and then inverted it in a small cistern (reservoir) of mercury. He noted that although the mercury dropped from the top of the tube it did not all run out – thus leaving a vacuum at the top of the tube. Over a period of time he realised that the variation of the height of mercury in the tube from day to day could be directly linked to the weather or changes in atmospheric pressure.
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