A Design for a Keyboard Instrument in Just Intonation
Chas. Williamson · The Journal of the Acoustical Society of America · 1939
In a keyboard instrument, the just scale may be closely approximated by setting up two equally tempered scales, one on the basis of A440.0, the other on the basis of A436.3, and mechanically selecting from them those frequencies which most nearly satisfy the appropriate ratios. Within one octave above middle C, no scale-step is in error by more than 0.6 vibration per second. The keyboard is exactly the same as that now used, and the instrument is playable in equal temperament when the performer so desires.