wet-bulb thermometer

A wet-bulb thermometer is an instrument used to measure humidity. It is part of a psychrometer, which also includes a dry-bulb thermometer. The bulb of the wet-bulb thermometer is covered with a moist cloth, typically muslin, that is soaked in water. As air moves over the wet cloth, water evaporates, cooling the bulb.123

The difference in temperature between the wet-bulb and dry-bulb thermometers, known as the wet-bulb depression, is used to calculate the dew point and relative humidity. The wet-bulb temperature indicates the lowest temperature to which something can be cooled by water evaporation and is a measure of how effectively the human body can cool itself through perspiration. This measurement is crucial for assessing heat stress and determining safe conditions for outdoor activities.423