barometre

A barometer is an instrument that measures atmospheric pressure. It is used in meteorology and aviation to help forecast weather and to calibrate other instruments. The term barometer derives from the Greek baros ('weight') and metron ('measure').

History: The mercury barometer was developed after Evangelista Torricelli in 1643, who filled a glass tube with mercury and inverted it into a reservoir, creating a column whose height balanced atmospheric pressure. Blaise Pascal demonstrated that pressure changes with altitude by performing experiments at different elevations.

Types: Mercury barometer measures pressure by the height of a mercury column. Aneroid barometer uses a sealed flexible metal diaphragm or capsule that expands or contracts with pressure changes, coupled to a pointer. Electronic or digital barometers use MEMS sensors to measure pressure and can display in various units.

Units and standard values: Atmospheric pressure is measured in pascals (Pa) or hectopascals (hPa). In meteorology, millibars (mb) are still used informally. Standard sea-level pressure is 1013.25 hPa (760 mmHg). Pressure decreases with altitude, and rapid drops can indicate approaching storms. Barometric readings are affected by temperature, instrument orientation, and local air flow; therefore calibration and context are important.

Applications and limitations: Barometers are foundational instruments in weather forecasting, aviation, and meteorology. They underpin altimeters in aircraft and many weather stations. Mercury barometers require careful handling due to toxic mercury; aneroid and electronic devices avoid liquid mercury but may drift and require periodic calibration. In practice, modern meteorology relies on networks of electronic sensors rather than traditional mercury instruments.