‹‹‹ Vitr. 5.4.7 | Table of Contents | Vitr. 5.4.9 ›››
8These names are given them from the number of tones which the voice passes through in going to them, counting that on which the voice begins as one; thus, moving through them to the fourth sound is called diatessarôn; to the fifth, diapente. to the eighth diapasôn, to the eleventh diapasôn with diatessarôn, to the twelfth diapasôn with diapente, to the fifteenth disdiapasôn.
8Their names are therefore due to numerical value; for when the voice becomes stationary on some one note, and then, shifting its pitch, changes its position and passes to the limit of the fourth note from that one, we use the term “fourth”; when it passes to the fifth, the term is “fifth.”