3. Ambrose decreed the use of the diatonic genus alone in 'church music; and it is probable that the chromatic and enharmonic genera soon fell into general desuetude, or only existed as curiosities for the learned.
The Jews are believed to have used a canon proceeding by thirds of tones, thus giving eighteen notes in the octave. It is stated that the Pythagorean canon has been developed into an Arabic scale of seventeen .sounds. ;