When we go to higher altitudes, the barometric height goes on decreasing, and right on top, where the atmospheric pressure is zero, the mercury column also dips to zero. This decrease is not uniform. At different ranges, the rate of decrease too is different. In modern barometers, mercury is not used. Such dial-type barometers are called ‘Aneroid barometers’. When such barometers are manufactured, instead of the pressure graduating, the corresponding height graduates. This instrument is called the ‘Altimeter’ and is used in aircraft by skydivers, mountaineers etc.
How is the height of different places on earth measured from the sea level?
The height of different places on earth is measured with the help of the ‘altimeter’. The instrument used for measuring the height at a place is basically a barometer. At sea level, the height of the barometric liquid (mercury) is 76 cm.