Fortin’s barometer is a laboratory instrument used to measure atmospheric pressure. It consists of a glass tube with a reservoir at the bottom and a vacuum at the top, which is closed with a brass screw. The tube is filled with mercury up to a certain level, and the height of the mercury column is measured using a scale attached to the side of the tube.

The barometer is calibrated so that the height of the mercury column corresponds to the atmospheric pressure at that location.

Fortin’s barometer is commonly used in meteorology and other scientific fields where precise measurements of atmospheric pressure are required. It is named after French instrument maker Jules Fortin, who designed the barometer in the mid-19th century.