Between the physical world of vibration, as measured by apparatus, and the world of consciously heard music there is a third area of investigation. Our auditory apparatus and/or mind separates different instruments and tones, hears some vibrations but not others, adds tones to fill out the sound spectrum, etc. This middle ground is the province of the psychology of music, a subject about which even many physical scientists know little. This introduction, by the developer of the Seashore test of musical ability, is a thorough survey of this field, the standard book for psychologists specializing in the area, for the school, and for interested musicologists. It opens with the musical mind and with a series of chapters on music as a medium: vibrato, pitch, loudness, duration, timbre, tone, consonance, volume, and rhythm, dealing with each from the special point of view of the role of psychology. It then moves to such factors as learning, imagining, and thinking in music; the nature of musical feeling; the relative sound patterns of specific instruments and the human voice; measures of musical talent; inheritance of musical ability; primitive music; the development of musical skills; and musical aesthetics. This wealth of material is supplemented with dozens of oscillograms and other sound-pattern charts recorded from actual play and singing by Jeritza, Caruso, Paderewski, Szigeti, Rethberg, Menuhin, Martinelli, and other artists. An appendix cites two attitudes toward the evaluation of musical talent and over 200 bibliographic references.