Answer to Question 1
The mercury barometer works based on the weight of mercury in the column equaling the weight of the same diameter column of air that extends from the ground to the top of the atmosphere. When air pressure increases, the mercury in the tube rises. Conversely, when air pressure decreases, so does the height of the mercury column. Instead of having a mercury column held up by air pressure, the aneroid barometer uses a partially evacuated metal chamber. The chamber is extremely sensitive to variations in air pressure and changes shape, compressing as the pressure increases and expanding as the pressure decreases. A series of levers transmits the movements of the chamber to a pointer on a dial that is calibrated to read in inches of mercury and/or millibars.
Answer to Question 2
The aneroid barometer is designed for home use with a dial face that indicates the relationship of air pressure to weather readings of fair or rainy and so on. It can also be easily connected to a recording mechanism, resulting in a barograph that provides a continuous record of pressure changes. This instrument is also a useful indicator of altitude for aircraft, mountain climbers, and mapmakers.
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