IN Chap, viii of his forthcoming work on “Some Questions of Musical Theory” (“From Seven to Seventeen”. Pp. 137–166. Cambridge: W. Heifer and Sons, Ltd., 1934. 2s. Qd. net), Dr. W. Perrett divides the octave into 171 intervals which he calls ‘hepts’. One sixth of a hept is the least difference of pitch which can be detected by a trained ear and Dr. Perrett shows that if the eleventh, thirteenth and nineteenth harmonics can be dispensed with, 50 of the intervals best known in music can be represented by integral numbers of hepts with errors of less than one seventh of a hept. Thus the fifth is 100, the fourth 71, the major third 55, the minor third 45. With an instrument constructed on these lines, modulation into any key would be possible, but if it were played by hand four players would be necessary. As an instrument with Bosanquet's 84 keys per octave was constructed at a moderate price half a century ago, the author considers that one with 171 is quite within the bounds of possibility at the present time.