[1] Michael Praetorius, _Theatrum Instrumentorum_, Wolfenbüttel, 1620,
pl. 14.
[2] _Ibid._, pl. 6.
[3] Querinus van Blankenburg, _Elementa Musica_, The Hague, 1739.
[4] Translation by Arthur Mendel in "Devices for Transposition in the
Organ before 1600," _Acta Musicologica_, 1949, p. 33.
[5] Sibyl Marcuse, "Transposing Keyboards on Extant Flemish
Harpsichords," _Musical Quarterly_, July 1952.
[6] Michael Praetorius, _Syntagma Musicum_, Wolfenbüttel, 1614-1620,
vol. 2 (Organographia), chapter 2.
[7] Translation by Arthur Mendel in "Pitch in the 16th and early 17th
Centuries, Part II," _Musical Quarterly_, April 1948.
[8] Marin Mersenne, _Harmonie Universelle_, Paris, 1636, p. 101.