What is used to measure humidity?

A hygrometer is an instrument used to measure the relative humidity in the atmosphere. There are several types of hygrometers, including:

1. Psychrometer: A psychrometer consists of two thermometers, one of which is dipped into a wet wick, and the other remains dry. The difference in readings between the two thermometers indicates the relative humidity.

2. Capacitive hygrometer: A capacitive hygrometer measures humidity by measuring the electrical capacitance of a material which varies with the amount of moisture it has absorbed.

3. Dew point hygrometer: A dew point hygrometer measures the dew point temperature, which is the temperature at which water vapor in the air condenses into liquid. This provides a direct measurement of the amount of moisture in the air.

4. Hair hygrometer: A hair hygrometer measures the length of a hair strand, which changes with humidity. At higher humidity, hair strands absorb moisture and stretch out, resulting in longer hair length.

These instruments are commonly used in meteorology, industrial applications, and in homes to monitor indoor environment.