Hermann von Helmholtz, Alexander John Ellis (1875). “On the Sensations of Tone as a Physiological Basis for the Theory of Music”, p.3, London : Longmans, Green and Company
Hermann von Helmholtz, Alexander John Ellis (1875). “On the Sensations of Tone as a Physiological Basis for the Theory of Music”, p.12, London : Longmans, Green and Company