The bulb of the wet bulb thermometer is always wrapped in a piece of wet cotton cloth.

The bulb of the wet bulb thermometer is always wrapped in a piece of wet cotton cloth so that when the wind blows, water from the wet bulb thermometer evaporates and thus lowers the temperature. Hence, the wet bulb thermometer records a temperature lower than the dry bulb thermometer. The difference in the readings of the dry bulb thermometer and wet bulb thermometer helps us to find the humidity in the air. The lesser the difference, the more humid is the air.