The trepidation talk'd, and that first mov'd.'
i.e. They pass the seven planetary spheres; then the sphere of fixed stars; then the crystalline or transparent one, whose swaying motion or libration measures the amount of the precession and nutation so often talked of; and then, the sphere of the primum mobile itself. But Milton clearly himself believed in the Copernican system; see Paradise Lost, viii. 121-140, where the primum mobile is described in the lines—
'that swift
Nocturnal and diurnal rhomb supposed,
Invisible else above all stars, the wheel
Of day and night.'
§ 18. [8]. compowned by 2 & 2. This means that in the best astrolabes, every almicantarath for every degree of latitude was marked; as may be seen in Metius. In others, including the one given by Chaucer to his son, they were marked only for every other degree. See Part II. sect. 5, l. 2.
§ 19. [7]. cenith, as here used, has a totally different meaning from that of senith, in l. 1 above. The senith in l. 1 is what we still call the zenith; but the cenith in l. 7 means the point of the horizon denoting the sun's place in azimuth. Contrary to what one might expect, the latter is the true original meaning, as the word zenith is corrupted from the root of the word which we now spell azimuth. The Arabic as-sant is a way or path; al-samt, a point of the horizon, and, secondly, an azimuthal circle. The plural of al-samt is assumūt, whence azimuth. But zenith is a corruption of semt, from samt al-rās, the Arabic name of the vertex of heaven (rās meaning a head); and the qualifying al-rās, the most important part of the phrase, has been improperly dropped. So far from the reading cenith being wrong here, it is most entirely right, and may be found (better spelt cenit) in the same sense in Messahala. See p. 213, second footnote. For cenith, some late copies have signet, evidently taken from the Latin word signum. They make the same mistake even in l. 12 of section 18.
§ 21. [4]. sterres fixes, fixed stars; here the s again appears in a plural adjective of French derivation; see note above, to § 5. 8. In MSS. Ii. 3. 3 and Ii. 1. 13 in the Cambridge University Library, is an interesting list of the 49 stars most usually placed upon the Astrolabe. The stars which are represented by the points of the tongues in [Fig. 2] are the same as those in the diagram from which Fig. 2 is copied, the original of which is in MS. A. I have slightly altered the positions of the points of the tongues, to make them somewhat more correct. The following is the list of the stars there shewn; most of their names are written in the MS. Cf. footnote on p. [186].
Within the Zodiac. In Aries, Mirach, or β Andromedæ, shewn by a short tongue above Aries; in Taurus, Algol, or β Persei, as marked; in Libra, Aliot or Alioth, i.e. ε Ursæ Majoris (the third horse, next the cart, in Charles's Wain), as marked; also Alramech, Arcturus, or α Boötis, shewn by the tongue projecting above Libra; in Scorpio, Alpheta, Alphecca, or α Coronæ Borealis, as marked; in Sagittarius, Raz Alhagus, or α Ophiuchi, near Alpheta; in Capricornus, Altair or α Aquilæ and Vega or α Lyræ, as marked, whilst near Vega is the unmarked Arided, or α Cygni; and in Pisces, Markab or α Pegasi.