Theon of Smyrna: Book on Astronomy

contrary to the common opinion of Plato and Aristotle, who believed there were four types of rhetoric: the deliberative, the judicial, and the demonstrative.

Finally, Gregorius Corinthius1, regarding the musical interval of the dis dia pente a perfect fifth plus an octave, or a twelfth, uses the authority of Theon’s commentaries, in which harmony is treated: about which Theon I would dare to affirm nothing.

However, Theon the mathematician is certainly someone else, distinct from our author. Ptolemy uses his observations of the greatest elongations from the Sun—one for Mercury, three for Venus2—and he is called Theon the ancient and Theon the ancient mathematician by Theon of Alexandria in his commentary on the ninth book of Ptolemy3. The four observations of that Theon, which Ptolemy utilized, were made in the 12th, 13th, 14th, and 16th years of the Emperor Hadrian. The first of Ptolemy’s own observations was made in the 11th year of Hadrian4, and the last in the 14th year of Antoninus Pius5. It is therefore clear that this Theon the mathematician flourished when Ptolemy was a young man. Moreover, that some familiarity existed between the young Ptolemy and this Theon, who was then flourishing or elderly, seems to be demonstrated by the fact that the observations of Theon, from which he chose four, are referred to by Ptolemy in one place as observations received from Theon6.

1 On Hermogenes' On the Method of Force, ch. 11, § 22, in Walz’s Greek Rhetoricians, vol. VII, p. 1127, lines 20-21.
2 Mathematical Composition, IX, 9; and X, 1-2; vol. II, pp. 176, 193, 194, 195, and 196 (Halma edition).
3 Pp. 390, 395, and 396 (Greek edition, Basel).
4 See Ptolemy’s Mathematical Composition, XI, 5, vol. II, p. 268 (Halma edition).
5 Ibid., X, 1, vol. II, p. 194 (Halma edition).
6 Ibid., IX, 9, p. 176.