baromètres

A barometer is a scientific instrument used to measure atmospheric pressure. Atmospheric pressure is the weight of the air in the atmosphere above a given point. Barometers are essential tools for meteorology, as changes in atmospheric pressure are closely related to weather patterns. When pressure rises, it generally indicates fair weather, while falling pressure often precedes stormy conditions.

There are two main types of barometers: mercury barometers and aneroid barometers. A mercury barometer consists of a glass tube filled with mercury, inverted into a dish of mercury. The atmospheric pressure pushes down on the mercury in the dish, causing the mercury in the tube to rise to a certain height. This height is then measured as the atmospheric pressure. Aneroid barometers, on the other hand, do not use any liquid. They contain a small, flexible, sealed metal box called an aneroid cell. As atmospheric pressure changes, the cell expands or contracts, and this movement is transmitted through a system of levers and springs to a needle that indicates the pressure on a calibrated dial. Aneroid barometers are more common today due to their portability and ease of use. Barometers are also used in various scientific and industrial applications, including altimetry, where they can estimate altitude based on the decreasing atmospheric pressure at higher elevations.