Barometers Realm

This Plexiglass Sympiesometer, made in the late 20th century by Denis Dingens, is a modern take on a historical instrument. The sympiesometer is a thermobarometer, in which atmospheric pressure is measured based on the position of a gas enclosed above a column of indicator liquid. It is also known as a tendency barometer: it does not display absolute pressure, but rather records changes (tendencies) using a movable scale that must be set manually.

The device consists of a slender tube with a sealed air chamber and a column of colored liquid (oil). The tube is open at one end and communicates with the atmosphere. As atmospheric pressure changes, the compressible gas (ordinary air) above the liquid contracts or expands, moving the liquid column up or down. Since the gas volume also depends on temperature, an alcohol thermometer with blue indicator fluid is mounted next to it. To take a reading, the user compares the height of the red oil column in the sympiesometer tube with the level of the fluid in the thermometer. Then, the plexiglass dial at the top of the instrument is rotated in relation to the concentric scale around it—rightward if the oil column is below the thermometer level, leftward if it is above. The scale is marked in empirical units from 0 to 8 in both directions, which correspond to the divisions of the main linear scale along the sympiesometer tube. This allows one to determine the barometric tendency, further illustrated on the concentric scale with small pictograms representing bad, variable, or good weather.