Final answer:
A mercury barometer is an instrument that measures atmospheric pressure using a column of mercury in a tube, with variations in mercury height reflecting changes in atmospheric pressure. It is essential for weather forecasting and can also function as an altimeter.
Step-by-step explanation:
Definition of a Mercury Barometer
A mercury barometer is an instrument used to measure atmospheric pressure. This type of barometer consists of a closed glass tube filled with mercury, with one end submerged in a mercury-filled basin and the other end sealed. The space above the mercury is a near-vacuum, allowing atmospheric pressure to exert force on the mercury in the basin, causing it to rise or fall in the tube. The height of the mercury column, often measured in millimeters of mercury (mm Hg), correlates directly with the atmospheric pressure. A change in height indicates a change in atmospheric pressure, providing valuable information for weather forecasting and altitude measurement. Mercury barometers are standard tools, so much so that units of mm Hg are commonly used to report atmospheric and blood pressures.
The relationship between the height of mercury (“h”), mercury's density (“p”), and gravity (“g”) against atmospheric pressure (“Patm”) is expressed as hpg = Patm. This means that the product of the mercury column height, its density, and the acceleration due to gravity is equal to the existing atmospheric pressure.