Whirling Hygrometer with Case – Overview The Whirling Hygrometer, also known as a Sling Psychrometer, is used for measuring relative humidity. It is made from two thermometers mounted on a frame which rotates around a handle and is whirled in the air by hand. One thermometer is covered with a tight-fitting muslin sock which is kept wet by (preferably) distilled water. This type of thermometer is known as the wet-bulb thermometer. The other is the dry-bulb thermometer and exposed to the atmosphere directly. Where the air is less than 100 per cent relative humidity, the wet bulb will display a lower temperature than the dry bulb known as wet-bulb depression. A special chart is used to convert the wet-bulb depression to relative humidity, or the relative humidity can be determined by correlating the readings with those on a simple slide rule, which is supplied with each instrument. Whirling Hygrometer with Case – Features Carry case Slide rule No mercury
