The interval between Ci and E1 is the sum of two Octaves and a Major Third, that is
Thus the interval between E1 and E' is the difference between the above, viz:
that is, a comma.
Now, in the Mean-Tone Temperament, each of the four Fifths above is flattened a quarter of a comma, and consequently the E1 thus obtained forms a perfectly true Major Third with the C. Thus, starting with 0 and tuning upwards two of these flattened Fifths, and a true Octave down, we obtain the notes C, G, and D ; then again starting from this D, and tuning up two of these Fifths, and another Octave down, we get the additional notes A and E, all the Fifths being a quarter of a comma flat, but being a true Major Third.
Now if we start from E, and repeat this process, that is, tune two of these flattened Fifths up, and an Octave down, and again two flat Fifths up, and an Octave down, we shall have obtained altogether the following notes: