Devices for measuring atmospheric pressure
Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere. An important application of the knowledge that atmospheric pressure varies directly with altitude was in determining the height of hills and mountains thanks to the availability of reliable pressure measurement devices. A barometer is one of the examples of scientific instruments used in meteorology to measure atmospheric pressure. A simple barometer consists of a long glass tube (closed at one end, open at the other) filled with mercury and turned upside down into a container of mercury. The barometer works by balancing the mercury in the glass tube against the outside air pressure, just like a set of scales.