AEROBIOLOGY is a synthesis: just as the geographer draws upon astronomy and geology, so the acrobiologist draws upon many sources. To under stand the environment of the air-spora we must go to meteorology. A fuller account of the relevant features of the atmosphere than that given here can be found in works on dynamical meteorology, e.g. Sutcliffe (1940), Geiger (195o), Sutton (1953), and U.S. Weather Bureau the last including many excellent diagrams.