Cistern barometers

From Glossary of Meteorology
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cistern barometer

A mercury barometer in which the lower mercury surface is larger in area than the upper surface.

The basic construction of a cistern barometer is as follows: A glass tube 1 m in length, sealed at one end, is filled with mercury, and then inverted. The tube is mounted so that its mouth penetrates the upper surface of a reservoir of mercury called the cistern of the barometer. Cistern barometers are classified according to whether the cistern is fixed in volume (
see Kew barometer) or variable in volume (
see Fortin barometer).