mercury barometer


noun

a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.

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Also called mercurial barometer.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

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What does mercury barometer mean?

A mercury barometer is a barometer with a column of mercury whose height varies according to the atmospheric (barometric) pressure.

A barometer is an instrument for measuring atmospheric pressure, which is used in forecasting the weather.

Mercury barometers are no longer in wide use, having been replaced by other methods of measuring pressure, such as aneroid barometers, which use a small capsule with flexible walls that expand or contract in response to changes in atmospheric pressure.

Why is mercury barometer important?

The mercury barometer was invented by Italian physicist and mathematician Evangelista Torricelli. He developed it in the mid-1640s after a suggestion from his mentor, the astronomer and physicist Galileo Galilei. French scientist Blaise Pascal later expanded on the fluid mechanics that Torricelli observed and used the mercury barometer to confirm that atmospheric pressure changes with altitude.

How can a bit of mercury predict the pressure of the atmosphere? The answer lies in the density of mercury and the ability to create a vacuum. A vacuum is an area of extremely low pressure. A vacuum can be created by filling a glass tube (such as a test tube) with some mercury and placing it top-down in a tub containing more mercury. The mercury in the tube presses down on itself and tries to flow out into the container. Pressure from the atmosphere presses on the mercury in the tub, and that forces the mercury up into the tube. Greater atmospheric pressure makes more of the mercury from the tub go into the tube, meaning the mercury goes higher, while less atmospheric pressure means less of the mercury gets forced into the tube and the level stays lower. You could do this with any liquid, but mercury’s high density compared to air means that you can use a tube that’s not too big.

Mercury barometers have fallen out of use because we’ve developed more accurate ways of measuring atmospheric pressure. That’s probably for the best, because mercury is very toxic. Although mercury barometers are now outdated as scientific instruments, they were a very important part of the history of science, helping to pave the way for improved weather forecasting and the field of meteorology.

Did you know ... ?

Evangelista Torricelli, the inventor of the mercury barometer, has a unit of pressure named after him. That’s the torr, defined as 1/760th of a standard atmosphere, which is a unit of measure equal to 101,325 pascals (yep, they’re named after Blaise Pascal).

What are real-life examples of mercury barometer?

Mercury barometers are no longer commonly used in scientific studies, but they are an important part of the history of science and meteorology.

 

 

Quiz yourself!

True or False? 

Mercury is used in mercury barometers due to its density.