Niecks, Frederick. The Flat, Sharp, and Natural. A Historical Sketch. Proceedings of the Musical Association, 16th Sess., (1889 - 1890), pp. 79–100.(JSTOR)
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Gould, Elaine (2011). Behind Bars: The Definitive Guide to Music Notation. London. p. 86. ISBN978-0571514564. OCLC701032248.{{cite book}}: CS1 maint: location missing publisher (link)