Pressure measurement

The mercury barometer

The mercury barometer consists of a long glass tube that is closed on one end. The open end of the tube is immersed into a container with mercury (quicksilver). A force acts downwards onto the surface of the mercury. This force is produced by the atmospherical air-pressure. The bigger the force that acts on the surface of the mercury the higher the mercury rises inside of the tube.

The mercury barometer was invented by Evangelista Torricelli in the 17th century. He also realised that the height of the mercury-column in the tub varied from one day to the other. This means that the atmospherical air-pressure also varies from day to day. With an air-pressure of 1 atm the mercury-column is 76mm high. Barometers can be used for weather forecasts. A high air-pressure indicates good weather, a low air-pressure indicates storm.