Hydrostatics is the study of the behavior of fluids at rest and the forces acting on them.
In hydrostatics, the height of a fluid column is directly proportional to the pressure exerted by that fluid. This relationship is known as Pascal's law and can be observed in the length of a mercury column in a barometer.
The length of a mercury column in a barometer is used to measure atmospheric pressure. It has been standardized to represent a unit of pressure known as the atmosphere (atm).
As the length of the mercury column increases, the atmospheric pressure decreases. This is because the weight of the mercury column exerts a downward force on the surface of the mercury in the barometer, creating a vacuum above it.
Mercury is a dense liquid and produces a larger change in height for a given change in pressure compared to other liquids. This makes it a more sensitive and accurate choice for measuring atmospheric pressure.