The temperature obtained by covering the bulb of a dry-bulb thermometer with a silk or cotton wick saturated with distilled water and drawing air over it at a velocity not less than 1000 ft/min. This is often accomplished by swinging the covered thermometer on the end of a string or rope. If the atmosphere is saturated with water vapor, the water in the wick will not evaporate and the dry and wet bulb temperatures will be the same. If the atmosphere is not completely saturated, the water will evaporate from the wick at a rate depedent upon the degree of saturation. The evaporation will cool the bulb and lower the temperature reading over that of the dry-bulb temperature to that of the wet-bulb temperature.