Elohopeabarometrin

Elohopeabarometrin, or the mercury barometer, is a device for measuring atmospheric pressure by means of a column of liquid mercury. It consists of a glass tube filled with mercury, inverted into a mercury-filled basin, creating a near-vacuum at the top of the tube. The height of the mercury column is read against a scale, typically in millimeters.

The operating principle is straightforward: atmospheric pressure supports the weight of the mercury column. When external pressure increases, the column rises; when it decreases, the column falls. The height of the column provides a direct measure of pressure. The unit most commonly used is the millimeter of mercury (mm Hg), with standard sea-level pressure defined as 760 mm Hg (1 atmosphere).

Historically, the mercury barometer was invented by Evangelista Torricelli in 1643 and played a crucial role in establishing the concept of atmospheric pressure. The mm Hg unit, also called torr in some contexts, was named in honor of Torricelli. Mercury barometers remain a foundational reference instrument in meteorology and atmospheric science, though modern practice often relies on aneroid and digital sensors for routine measurements.

Usage and limitations: Mercury barometers require careful handling due to the toxicity of mercury and the risk of glass breakage. Readings can be affected by temperature, which changes mercury density and thus column height. They require stable mounting and calibration. In contemporary meteorology, mercury barometers are largely superseded for daily weather monitoring, but may still be used in education, research, or calibration laboratories, and as historical exemplars of barometric measurement.