Coolers in which atmospheric air is blown by a fan, through a nest of pipes, into a tower or chamber in which it comes into intimate contact with fine particles of water from atomizing nozzles. By the evaporation of some of this water the air rapidly becomes saturated at the wet-bulb temperature, the remaining water running off at the same temperature. This water is collected and pumped back through the nest of pipes, thereby cooling the air before it enters the spray chamber. The entering air then has a lower drybulb temperature than the atmosphere and, since its moisture content is unaltered, the wet-bulb is lower also.