Wet & Dry Thermometers

A Wet & Dry Bulb thermometer consists of two thermometers, one of which is dry and one which is kept moist with distilled water on a sock or wick is called wet. The two thermometers are thus called the dry-bulb and the wet-bulb. At temperatures above the freezing point of water, evaporation of water from the wick lowers the temperature, so that the wet-bulb thermometer usually shows a lower temperature than that of the dry-bulb thermometer. When the air temperature is below freezing, however, the wet-bulb is covered with a thin coating of ice and may be warmer than the dry bulb. Relative humidity is computed from the difference in temperatures as shown by the wet-bulb and ambient temperature as shown by the dry-bulb thermometers.