Laurence Sterne (1805). “The Works of Laurence Sterne, A. M.: A sentimental journey through France and Italy. The Koran: or, The life, character and sentiments of Tria Juncta in Uno. A political romance”, p.356
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