Theory of the Binaural Location of Pure Tones.-It is pointed out that to determine two coördinates of the sound source, angular position and distance, the simultaneous observation of both phase difference and intensity ratio for the two ears is necessary. Thus, contrary to the conclusions of certain observers, intensity ratio plays an important part in sound location. Using a method of analysis due to Stokes, the authors have prepared a series of charts showing the intensity ratio and phase difference for sources at various distances and angular positions emitting sound with a frequency from 310 to 1,860 cycles and for two angular separations of the ears, 165° and 180°, assumed to be placed on a spherical head. These charts show the theoretical position of the source for any combination of phase difference and relative intensity which might occur with actual sources. Experiments to test this theory are suggested. When unnatural combinations occur as a result of distortion of the sound in transmission or are produced artificially in the laboratory, the interpretation of the stimuli will depend on psychological factors and cannot be explained by any purely physical theory alone. Psychological Readjustment of Unnatural Combinations of Binaural Stimuli.-Suggestions as to the nature of these adjustments are advanced and the results of laboratory experiments with such unnatural combinations are interpreted with the assistance of the charts and are shown to be in agreement with this theory.