Barometers Realm

This Plexiglass Psychrometer, produced in the late 20th century by Denis Dingens, is a modern interpretation of a classical instrument for measuring relative humidity. The psychrometer belongs to the category of meteorological instruments based on a simple yet highly precise physical phenomenon — evaporative cooling. It determines air humidity by comparing the readings of two thermometers, one dry and one wet, using a printed reference table.

The instrument consists of two capillary thermometers calibrated in degrees Celsius from 0 to 50 °C, mounted on the front face of a transparent plexiglass panel measuring 42 cm in height, 10 cm in width, and 1 cm in thickness. The right-hand thermometer is the dry bulb, showing the ambient air temperature, and contains red indicator fluid. The left-hand thermometer is the wet bulb, its reservoir wrapped in a fabric wick whose end is immersed in water held in a glass container at the base of the instrument. As water evaporates from the wick, the wet bulb cools, and its temperature drops below that of the dry bulb. The wet thermometer contains blue fluid for visual distinction.

To obtain accurate readings, the wick of the wet bulb must be properly moistened. After allowing both thermometers to stabilize over several minutes, the dry bulb temperature is identified first in the top horizontal row of the table, followed by the temperature difference between the dry and wet bulbs, which is located in the left vertical column. The cell at the intersection of the two values gives the relative humidity as a percentage.