What Is a Barometer?

Barometer History
The barometer dates back to 1643, when Italian scientist Evangelista Torricelli used a 34-foot tube filled with water to measure air pressure. As weather patterns shift, the "weight" on the water changes, which causes the column to move up or down. Perfecting the design, Torricelli replaced water with mercury, which allowed the use of a much smaller tube. While water used a 34-foot tube, mercury accurately recorded pressure in a 3-foot tube.

How Does a Barometer Work? Mercury barometers are made from glass tubes. With one end sealed, the barometer tube is filled with mercury. Heated to release extra air, the tube is then inverted in a small cup of mercury. As the mercury sinks, it creates a vacuum in the tube. Atmospheric pressure on the small cup keeps the mercury column steady. As the atmospheric pressure changes, the mercury column adjusts its height, giving a reliable reading on the barometer.

Barometers in Plain English
Atmospheric pressures push down on the mercury reservoir, which in turn forces mercury up into the column. As pressures decrease, the atmospheric weight on the reservoir is eased, and the mercury column shrinks. As pressures increase, the column goes up.

Predicting Weather with Barometers
Weather and atmospheric pressure are intimately related. As such, barometers play a crucial role in predicting weather. High pressures in the area mean stable weather and high readings on barometers. When a barometer drops, that means a stormy low pressure cell is moving in. Conversely, a rise on the barometer means heavy, stable air is moving into the area.

Barometers are practical and educational instruments. Commercial and professional barometers are available for a wide range of purposes. For more information on weather forecasting or barometer uses, check out WeatherStations.com and other weather-related websites.