It is perhaps worth while to collect three striking cases where the history of music impinges on that of classical scholarship. My sources are not recondite, but I find that, for I the obvious source, the ‘Bach Reader’, is misleading; for II the evidence is mostly to be found in Grove; for III the only fairly detailed account I know is in Nieck's Robert Schumann (1923, pp. 47 ff.), now difficult to find, which I supplement from the preface to the 1828 Forcellini.
I. From a (Latin) note on Quintilian (i. 12.3, ed. 1738: not in the later editions) by Gesner, a first-rate scholar and lexicographer, who was Rector of the Thomasschule when Bach was Cantor. It is interesting to contrast Gesner's enthusiastic appreciation with his successor Ernesti's contemptuous indifference—which suggests that there is more to be said for Bach in his quarrel with Ernesti than we are sometimes led to suppose.
Quintilian is speaking of the brilliant performances of musicians; Gesner comments: ‘All this you (sc. Quintilian) would think of little consequence if you could return from the other world and see Bach playing with both hands and all his fingers, on an instrument which seems to combine many citharas in one—the organum organorum, running over it hither and thither with both hands and swiftest motion of the feet, eliciting many varied passages and sounds diverse yet unified—if you could see him, I say, doing a thing which several citharists and innumerable tibicines could not do, and not, like a citharoedus, playing only his own part, but equally watchful of all the symphoniaci, to the number of 30 or 40; calling this one to attention by a nod, another by a stamp of the foot, a third by a warning finger; giving the right note to one from the top of his voice, to another from the bottom, and to a third from the middle of it.