Humid air

The dew point temperature is the temperature where water vapor starts to condense out of the air or the temperature at which air becomes completely saturated with water vapor. Above this temperature the moisture stays in the air. If the dew point temperature is close to the dry air temperature, the relative humidity is high. If the dew point is well below the dry air temperature, the relative humidity is low.

The wet bulb temperature is the adiabatic saturation temperature. In other words, the wet bulb temperature is the lowest temperature that can be reached under current ambient conditions by the evaporation of water only. The wet bulb temperature can be measured by using a thermometer with the bulb wrapped in wet muslin. The adiabatic evaporation of water from the thermometer bulb and the cooling effect is indicated by a "wet bulb temperature" lower than the "dry bulb temperature" in the air.