Why is the reading of the wet thermometer of the psychrometer always lower than the air temperature in the room?

As the name suggests, a psychrometer’s wet thermometer should always be wet. In this case, moisture from its surface evaporates, taking heat with it. The evaporation process occurs due to the “jumping out” of the fastest liquid molecules from its surface and volatilizing them in the form of vapor. Because of this, the average internal energy of the remaining molecules decreases, the temperature of the wet bulb too.