Sling Psychrometer
In a sling psychrometer, two thermometers are attached to a handle and spun in the air for a few minutes. One thermometer is not covered (i.e. dry-bulb thermometer); the other has a cloth wick over its bulb and is called a wet-bulb thermometer.
To determine relative humidity, the cloth wick is dipped in water and the instrument spun around by its handle. During the spinning, the water evaporates from the wick, cooling the wet-bulb thermometer. Using charts, the difference between the wet and dry-bulb temperature, indicates relative humidity.
