of twelve mathematical scales is that F# and G?, which in the tempered system are one, being counted the same, are made two scales in the mathematical; but it is a needless nicety. Twelve is the natural number and period for both mathematical and tempered scales. And as the system of twelve Fifths contains the key system of music four times, only three of these twelve Fifths being required for any one key, it follows that the tempered key is affected by only one-fourth part of the small amount to be tempered into the whole twelve. [Scientific Basis and Build of Music, page 30]
See Also