Hygrometer with wet and dry bulb thermometers, made by Accoson, London, c. 1960s. The thermometers are set on a white glass plate marked with scales from 20 to 100 degrees Fahrenheit. The instrument was used by amateur weather observer Bill Poole during the 1960s and 1970s.

This type of hygrometer provides a measurement of relative humidity of the atmosphere by comparing the readings of two thermometers. One thermometer has its mercury bulb open to the air, and the other is kept wet with a cloth soaked in distilled water.

Bill Poole was a keen amateur weather observer who supplied his meteorological readings to the National Meteorological Archive to be added to the national database.