Today’s Topic: Barometers
Q: How long have been barometers been around?
A: At least 400 years, says Brent McRoberts of Texas A&M University. Barometers, which are used to measure air pressure – which in turn can give us one measuring stick of predicting the weather – were invented in the 1640s in Italy. "Scientists back then noticed that the level of mercury in glass tubes tended to vary from day to day," McRoberts says. "They further noticed that this seemed to coincide with changes in the weather. In the late 1600s and early 1700s, more barometers were made in England than anywhere in the world, and some had unusual shapes - some resembled clocks, others looked like large banjos and others were in the shape of large wheels. Mercury was used in all barometers back then, and even though it is toxic, it proved to be the best liquid for measuring air pressure. A change in the level of the mercury indicates high pressure or low pressure - falling pressure usually means possible stormy weather, while a rising barometer means fair weather."
Q: Have they changed much over the years?
A: A big change occurred in 1840, when a Frenchman named Lucien Vidie made the first barometer that had no fluid, called an aneroid. "The tube that had contained mercury was replaced with one that had a metal vacuum disc," McRoberts says. "This type was a little less accurate, but it could be made smaller and was easily carried on ships or outdoors. There is quite a large market today for antique barometers, and it's a worldwide market. Many of the barometers that were made several hundred years ago can still be found in antique shops and stores, and some of these sell for $5,000 and up. The unique style and condition of the barometer plays a big part in its price."
Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.
For more news about Texas A&M University, go to http://tamunews.tamu.edu/.
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