BarometerA barometer is an instrument used to measure atmospheric pressure. It allows you to measure the pressure exerted by the atmosphere using water, air or mercury. From the variation in atmospheric pressure, we can predict short-term weather changes. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay A barometer is an instrument for measuring the pressure of, due to the weight of the column of air above it. As the Earth's atmosphere becomes thinner with increasing height, it follows that as we rise from sea level and lower parts of the Earth's surface, the weight of the air decreases . That is, the pressure will drop. Types: Water-based barometers This concept of "decreasing atmospheric pressure predicts stormy weather" forms the basis of a primitive weather forecasting device called weather glass or glass tender. it consists of a glass container with a sealed body, half filled with water, a narrow spout connects to the body below the water level which rises above the water level, where it is open to the atmosphere. when the air pressure is lower than it was at the time the body was sealed, the water level in the spout will rise above the water level in the body, when the pressure air is higher than it was when the body was sealed, the temperature of the water level in the spout will increase the water level in the spout. A variation of this type of barometer can be easily constructed.Mercury barometersA mercury barometer has a glass tube at least 84 cm high, closed at one end, with an open reservoir filled with mercury at the base. The weight of the mercury creates a vacuum in the top of the tube. The mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the tank. High atmospheric pressure exerts more force on the reservoir, pushing the mercury higher up the column. The low pressure allows the mercury to descend to a lower level in the column by reducing the force exerted on the reservoir. Since a higher temperature at the instrument will reduce the density of the mercury, the mercury height reading scale is adjusted to compensate for this effect. One atmosphere of pressure is equivalent to approximately 29.9 inches, or 760 mm, of mercury. Some barometers give atmospheric pressure in millibars (one millibar = 100 pascals, or one pascal hecter) To convert a reading in inches of mercury to millibars, divide the pressure in inches of mercury by 0.0295. Aneroid barometer An aneroid barometer uses a small flexible metal box called an aneriode cell. This aneriod capsule (cell) is made from beryllium and copper. The box is sealed tightly after being removed for part of the year, so that small changes in external air pressure cause the cell to expand or contract. This expansion and contraction results in mechanical levers and other devices displayed on the anriod barometer dial. Many models include a manually adjusted needle that is used to mark the correct measurement so that a change can be seen. Standard atmospheric pressure the standard atomsphere (symbol; atm) is a unit of pressure equal to 101325 Pa or 1013.25 millibars or hectopascals. This is equivalent to 760 mmHg (torr), 29.92 inches Hg 14.696 psi. The density of mercury will change with temperature, so a reading must be adjusted for the temperature of the instrument. For this purpose, a mercury thermometer is usually mounted on the instrument. Like the pressure.