The barometer works by balancing the weight of mercury in the glass tube against the atmospheric pressure, much like a set of scales. ... If the weight of mercury is less than the atmospheric pressure, the mercury level in the glass tube rises (high pressure).A mercury barometer is a device that is used to measure the atmospheric pressure at a given location. ... It is an absolute pressure gauge. The air is evacuated from the long, hollow, and vertical glass tube which sits in mercury. A mercury barometer is also known as a Torricellian Barometer.
Air pressure pushes down on the surface of the mercury, making some rise up the tube. The greater the air pressure, the higher the mercury rises. You can read the pressure off a scale marked onto the glass.Mercury is commonly used in barometers because its high density means the height of the column can be a reasonable size to measure atmospheric pressure. A barometer using water, for instance, would need to be 13.6 times taller than a mercury barometer to obtain the same pressure difference.Vanos said people are most comfortable with barometric pressure of 30 inches of mercury (inHg). When it rises to 30.3 inHg or higher, or drops to 29.7 or lower, the risk of heart attack increases.
Water is not a suitable barometric liquid because: (i) The density of water is low (103 kg m-3). Water barometer will support 10.4m of water at sea level. It is impractical to have such a long tube.In barometer. In the mercury barometer, atmospheric pressure balances a column of mercury, the height of which can be precisely measured. To increase their accuracy, mercury barometers are often corrected for ambient temperature and the local value of gravity.A barometer is essentially a balance. The weight of the atmosphere is balanced by the weight of a much shorter mercury column. You can't use an ordinary pan balance to weight the atmosphere (because air is pushing down on both sides).