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Relative humidity is measured using the wet bulb and dry bulb methods because these techniques take advantage of the principles of evaporative cooling and the temperature differences associated with moisture in the air.

The dry bulb temperature is simply the air temperature measured by a standard thermometer, while the wet bulb temperature is measured using a thermometer with a wetted bulb that cools as water evaporates. The difference between these two temperatures can be used to calculate relative humidity, as it reflects how much moisture the air can hold versus how much moisture is actually present in the air.

When the air is saturated and holds maximum moisture, the wet bulb temperature will be equal to the dry bulb temperature. Conversely, if the air is dry, the wet bulb temperature will be significantly lower than the dry bulb temperature due to the enhanced evaporative cooling effect.

Thus, utilizing both the wet bulb and dry bulb temperatures allows for an accurate assessment of relative humidity, which is crucial in various applications, including meteorology, HVAC systems, and agricultural practices.