The principle of the hygrometer measuring complete relative humidity: because the temperature-sensing bubble of the wet-bubble thermometer is wrapped with cotton yarn, the lower end of the cotton yarn is immersed in water, and the temperature of the wet-bubble thermometer is always lower than that of the dry-bubble thermometer due to the evaporation of water. The temperature difference is related to the speed of water evaporation (that is, the relative humidity at that time). According to the readings of the two thermometers, the relative humidity of the air can be found from the table or curve.
