A little out of tune
On the shift from just intonation to equal temperament, which I’ve discussed elsewhere, cf. this passage from a 1910 lecture by one Alfred Daniell to the Honourable Society of Cymmrodorion entitled “Some remarks on certain vocal traditions in Wales”:
Violins and their kindred generally can produce the true harmonic scale, or any other scale; so, they say, can trombones but harpsichords and other instruments of fixed pitch led to horrible results if they were tuned to the key of C or G or F with pure intervals in the harmonic scale of that key. You had to keep to the key for which the instrument was tuned; if you ventured on transitions, or played in other keys, the instrument gave beats and was said to bay like a wolf. If you wanted to avoid this you must have an impracticable number of keys to the octave on the harpsichord or organ. The difficulty came to a head in the time of John Sebastian Bach, who cut the Gordian knot by splitting the difference. “Don’t try to put anything exactly in tune put everything a little out of tune; make the octave consist of twelve exactly equal semitones. We know that’s wrong, but we shall get accustomed to it.” Such was his advice, and all the advances of orchestral music since his day have been rendered possible through everything being a little out of tune.
(I encountered this passage in a quotation of one of David Jones’ letters.)