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Monitoring Pressure Changes

In a 17th century laboratory in Florence, Italy, Evangelista Torricelli- physicist mathematician, and assistant to the astronomer Galileo - filled a long glass tube with mercury and turned it upside down into a dish forming a vacuum so that the mercury remained held within the tube. To his amazement, he witnessed that the mercury was not the same height everyday. The changes in its level were caused by changes in the atmospheric pressure. Torricelli had not only created a vacuum, but also a very important weather instrument - the barometer.

Barometers are weather instruments used to measure air pressure and they are significant tools for today’s meteorologists. The amount of pressure is indicated by mercury inside the barometer. The mercury level is pushed up when air pressure is high.

Air pressure is regularly recorded as inches of mercury (Hg), indicating how high or low the mercury inside a barometer rises or falls. It is also reported in millibars (mb) on weather maps. Today, scientists often use a more modern technique to measure pressure directly in units called hectopascals (hPa).