At constant vapor pressure, the relative humidity decreases as the temperature increases, therefore, at higher temperature the relative humidity is low and water readily evaporates from the wet bulb thermometer that results in the cooling of the bulb such that at a given ambient temperature the very low relative humidity results in very large differences between the temperatures of the wet bulb thermometer and that of the dry bulb thermometer and the wet bulb is observed to be the colder thermometer of the two
