Air

The barometer

The most precise and accurate instrument to measure pressure is the mercury barometer, on the model of  E. Torricelli’s barometer invented in 1643.  The aneroid barometer is less precise, however it is smaller and easier to use.  It consists of a metal container in which a  forced vacuum is created and sealed with a light flexible metal cover that rises and falls with variations in the external pressure. The movements of the cover are transformed by a mechanism into movements of a needle along a measuring scale that indicates the value of the atmospheric pressure.
By changing the values on the reference scale, aneroid barometers can be used as altimeters, to measure the height above sea level.
In a weather station, barographs are utilized. These are barometers coupled with a system to indicate the variations in the pressure graphically on a strip of paper. At present electronic instruments are able to transmit data directly to the processing stations and to record them on a computer.