A barometer is a device that measures the atmospheric pressure of the air. It can also measure altitude---distance above sea level---as the pressure changes at different levels. The first barometer was a tube 34 feet long filled with water but the design was soon changed to use a much smaller tube and dense mercury.

Origin

The Italian scientist Evangelista Torricelli, a friend and student of Galileo, invented the first barometer in 1634.

Workings

Changes in atmospheric pressure will cause the mercury level in a sealed tube to raise or lower. Standard air pressure at sea level and in a temperature of 15 degrees C is typically measured at 1,013 millibars. As the pressure on the mercury in ordinary barometers increases or decrease, the dial moves to indicate the level of atmospheric pressure.

Weather Forecasting

A change in atmospheric pressure can often indicate a change in the weather patterns. When under a higher pressure system, the barometer can read over 30.2 inches and would typically point toward fair weather. But a reading of under 29.8 inches could be a precursor to the arrival of a low pressure system bringing rain or stormy weather.

Normal Changes

Changes in pressure of .02 to .10 inches are normal daily changes in atmospheric pressure and do not typically indicate upcoming changes in the weather. Winter months will have greater changes in pressure than those of summer months.

Other Barometer Types

An aneroid barometer is a device that does not use mercury or any other liquid but instead uses the bending of a metallic surface to move a pointer and indicate atmospheric pressure levels.

Source:

Science Company

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