De institutione musica I.27: Qui nervi quibus sideribus comparentur.
This only seems meanwhile to be added about the upper tetrachords: that from the hypate meson to the nete there is, as it were, a certain pattern of the heavenly order and distinction. For the hypate meson is assigned to Saturn, the parhypate is like the circle of Jupiter. They gave the lichanos meson to Mars. The Sun has the mese. Venus has the trite synemmenon, Mercury rules the paranete synemmenon. The nete holds the pattern of the lunar circle. But Marcus Tullius makes the contrary order. For in the sixth book of On the Republic he says thus: “And nature brings it about that the extremes sound grave on the one side and acute on the other. For this reason that highest star-bearing course of heaven, whose revolution is swifter, is moved with an acute and stirring sound, but this lunar and lowest with the gravest. For the ninth, the earth, remaining immovable, clings always to one seat.” Here, then, Tullius places the Earth as silence, being immovable. After this, the one next to silence he gives the Moon with the gravest sound, so that the Moon is proslambanomenos, Mercury hypate hypaton, Venus parhypate hypaton, the Sun lichanos hypaton, Mars hypate meson, Jupiter parhypate meson, Saturn lichanos meson, the farthest Heaven mese. Which of these are immovable, which wholly movable, and which stand between the immovable and the movable, there will be a more fitting place to explain when I treat of the division of the regular monochord.