[142] “ac trigesimo anno ad brevissima sedis suæ principia regredi;” I confess myself unable to offer any literal explanation of this passage; nor do the remarks of the commentators appear to me satisfactory; see Hardouin and Alexandre in Lemaire, ii. 241, 2. It is translated by Ajasson “en trente ans il reviens à l’espace minime d’où il est parti.” The period of the sidereal revolutions of the planets, as stated by Mrs. Somerville, in her “Mechanism of the Heavens,” and by Sir J. Herschel, in his “Treatise on Astronomy,” are respectively as follows:—
| days. | days. | |
|---|---|---|
| Mercury | 87·9705 | 87·9692580 |
| Venus | 224·7 | 224·7007869 |
| Earth | 365·2564 | 365·2563612 |
| Mars | 686·99 | 686·9796458 |
| Jupiter | 4332·65 | 4332·5848212 |
| Saturn | 10759·4 | 10759·2198174 |
| Somerville, p. 358. | Herschel, p. 416. | |
[143] “‘mundo;’ hoc est, cœlo inerrantium stellarum.” Hardouin, in Lemaire, ii. 242.
[144] Our author supposes, that the spectator has his face directed towards the south, as is the case with the modern observers. We are, however, informed by Hardouin, that this was not the uniform practice among the ancients; see the remarks of Alexandre in Lemaire, ii. 242, and of Marcus in Ajasson, ii. 269.
[145] The constant revolution refers to the apparent daily motion; the opposite direction to their annual course through the zodiac. Ptolemy gives an account of this double motion in his Magna Constructio, i. 7.
[146] For the exact period, according to Somerville and Herschel, see note [142], p. 27.
[147] Aristotle informs us, that Mars was also called Hercules or Pyrosis; De Mundo, cap. ii. p. 602. See also Apuleius, De Mundo, § 710. Hyginus is said by Hardouin to give the name of Hercules to the planet Mars, but this appears to be an inaccuracy; he describes the planet under its ordinary appellation; lib. ii. p. 62; and ii. 78, 9.
[148] Cicero, speaking of the period of Mars, says, “Quatuor et viginti mensibus, sex, ut opinor, diebus minus;” De Nat. Deor. For the exact period, see note [142], p. 27.
[149] “Sed ut observatio umbrarum ejus redeat ad notas.” According to the interpretation of Hardouin, “Ad easdem lineas in solari horologio.” Lemaire, ii. 243.
[150] This is an example of the mode of computation which we meet with among the ancients, where, in speaking of the period of a revolution, both the time preceding and that following the interval are included.