*pendulum* where *fourth* the length is *double* the oscillations. A third condition in this order is in *springs* or *reeds* where *half* the length is *four times* the vibrations. If we take a piece of straight wire and make it oscillate as a pendulum, one-fourth will give double the oscillations; if we fix it at one end, and make it vibrate as a spring, half the length will give four times the vibrations; if we fix it at both ends, and make it vibrate as a musical string, half the length will produce double the number of vibrations per second.

G# as it occurs in the scales of A, E, and B major, and A♭ as it occurs in the scales of F and B♭ minor, are only distant the *apotome minor*, and are well represented by one key of the piano. It is only G# as it occurs in the scale of F six sharps major, and A♭ as it occurs in the scale of E six flats minor, that is not represented on the piano. These two extreme notes F# and E♭ minor are at the distance of fifteenth fifths and a minor third from each other. This supplies notes for 13 major and 13 minor mathematical scales; but as this is not required for our musical world of twelve scales, so these far-distant G# and A♭ are not required. The piano is only responsible for the amount of tempering which twelve fifths require, and that is never more than *one comma* and the *apotome minor*.

The difference between B# and C♮ is the apotome minor - a very small difference - and this can only occur in the mathematical scales. In tempered scales, such as are played on the piano, one key serves equally well for both. Although seven sharps may be employed, seven black keys are necessary. As F# and G♭ have the same relation to each other as B# and C♮, and as B# does not require a black key but is found on a white one, so all the semitonic necessities for twelve tempered scales are fully supplied by 5 black keys, since the white keys are as much semitonic as the black ones.

If we may add a note to a chord, we may also *vice versa* add that chord to that note. If we may add F to the dominant chord G B D f, we may add the dominant chord to F, thus, g b d F, in some other [Scientific Basis and Build of Music, page 80]