Abstract: A wet bulb thermometer. A temperature sensor which can function in a moist environment is placed in such a location that it will be within the mist of water produced by a nozzle when pressurized water is supplied to the nozzle. Preferably, the temperature sensor is placed somewhat below the nozzle to account for the effect of gravity upon the mist of water. Also, preferably, the temperature sensor produces an electrical signal that is indicative of temperature and that can be read by a computer. Accuracy of the determination of the wet-bulb temperature of the air is assured by the redundancy of this device. Evaporation from droplets in the mist assure that the temperature of the air within the mist is at the wet-bulb temperature as, independently, does the evaporation from the film of water which forms on the surface of the temperature sensor.