23. Johann Nikolaus Forkel, Musikalisch-kritische Bibliothek, II (Gotha: C. W. Ettinger, 1778; reprint Hildesheim: Georg Olms, 1964), 281–93. For an appreciation of Forkel’s study, see my “The New Modulation of the 1770s: C. P. E. Bach in Theory, Criticism, and Practice,” Journal of the American Musicological Society 38 (1985), 551–592, esp. 573–574.