Test data of forced draft cooling towers is all too meager, and that available is, in many instances, incomplete. It is the opinion of the authors that putting cooling tower design on a rational basis can be brought about only by two methods. Either complete and intensive study of all existing towers or a thorough study of models, similar to the research conducted on airplanes in wind tunnels and on boat hulls in towing tanks, is necessary. Models used should be so constructed that quantity, condition, and velocity of air; quantity and condition of water; and type and arrangement of filling may be controlled. It is by the second method that the authors believe rational tower design may best be brought about.