The Coriolis force is a fictitious force exerted on a body when it moves in a rotating reference frame. It is called a fictitious force because it is a by-product of measuring coordinates with respect to a rotating coordinate system. The instrument is made up of two identical thermometers, one a wet bulb, and the other a dry bulb. When the thermometers are ventilated the wet bulb temperature will be lower than the dry bulb temperature. To understand how the psychrometer works we need to know a little more about Latent Heat and Evaporation.
Latent heat is the energy taken up by the air as water changes phase.
Latent heat is the key to understanding many aspects of weather, as it is the main source of energy for thunder storms and hurricanes. In the psychrometer, moving air molecules collide with the liquid water molecules in the damp wicking. This gives some of the water molecules enough energy to speed up and break away from the liquid as water vapour and a cooling effect is obtained. This is the same effect seen in the cooling of the human body by perspiration. Fast-moving, warm air molecules collide with liquid water molecules.