Barometers measure the amount of pressure in the air around you. Barometers use mercury to measure air pressure, which is dependent upon the weather and the elevation of your location, such as at sea level or on a mountain top.

Uses

Meteorologists use barometers to help predict the weather by measuring changes in air pressure. When including variable wind patterns with barometers, short term weather predictions can be very accurate.

Explanation

NASA points out that although air molecules are invisible to the human eye, they still "have weight and take up space." Air molecules are always under some amount of pressure. When the molecules are compacted, it is said that the molecules are under high pressure.

Significance

High air pressure indicates cool weather and clear skies are on the way. Low pressure indicates warmer weathers and potential storms.

History

The mercury barometer was created in 1643 by Evangelista Torricelli. While other inventors attempted to make barometers, no other working models were found prior to 1643.

Styles

Decorative barometers for the home commonly display the air pressure, temperature and time. Decorative barometers may be less accurate then scientific models.

Types

Weather forecasters commonly use aneroid barometers because they are more accurate and compact than mercury thermometers, and can record data for up to a week. Aneroid barometers use a small metal box containing an alloy cell; changes in pressure cause the alloy cell to expand and contract, measuring weather changes.

Source:

NASA.gov: How Air Pressure Effects You

USA Today: How a Barometer Measures Air Pressure

USA Today: Aneroid Barometer

More Information:

Weather Instruments Online: Barometers

Weather Equipment: Barometers