על בריאת העולם ט״וOn the Account of the World's Creation 15
א׳
1[47] This is the reason why the earth put forth plants and bore herbs before the heaven was furnished. But the heaven was afterwards duly decked in a perfect number, namely four. This number it would be no error to call the base and source of 10, the complete number; for what 10 is actually, this, as is evident, 4 is potentially; that is to say that, if the numbers from 1 to 4 be added together, they will produce 10, and this is the limit set to the otherwise unlimited succession of numbers; round this as a turning-point they wheel and retrace their steps.
ב׳
2[48] 4 also contains the ratios of the musical consonances, that produced by an interval of four notes, and that produced by an interval of five, and the octave and double octave as well. And it is out of these that the most perfect concord is produced. Of that produced by an interval of four notes the ratio is 1⅓, of that produced by an interval of five 1½, of the octave 2, of the double octave 4. All these the number 4 embraces in itself, 1⅓ in the ratio 4:3; 1½ in the ratio 6:4; 2 in the ratio 4:2; 4 in the ratio 4:1.