those of the 7 planets, the _firmamentum_ (_stellarum fixarum_), the _nonum coelum_, _decimum coelum_, _primum mobile_, and _coelum empyræum_. 18. See fig. 5, Pl. III. This is made upon the alt-azimuth system, and the plates are marked according to the latitude. The circles, called in Latin _circuli progressionum_, in Arabic _Almucantar[=a]t_, are circles of altitude, the largest imperfect one representing the horizon (_horizon obliquus_), and the central dot being the zenith, or pole of the horizon. In my figure, they are 'compounded by' 5 and 5, but Chaucer's shewed every second degree, i.e. it possessed 45 such circles. For the method of drawing them, see Stöffler, leaf 5, back. 19. Some Astrolabes shew 18 of these azimuthal circles, as in my figure (fig. 5, Pl. III). See Stöffler, leaf 13, where will be found also the rules for drawing them. 20. If accurately drawn, these _embelife_ or oblique lines should divide the portions of the three circles below the _horizon obliquus_ into twelve equal parts. Thus each arc is determined by having to pass through three known points. They are called _arcus horarum inequalium_, as they shew the 'houres inequales.' 21. In fig. 2, Pl. II, the _Rete_ is shewn as it appears when dropped into the depression in the front of the instrument. The shape of it varied much, and another drawing of one (copied from Camb. Univ. MS. Ii. 3. 3, fol. 66 _b_) is given in fig. 9, Pl. IV. The positions of the stars are marked by the extreme points of the metal tongues. Fig. 2 is taken from the figures in the Cambridge MSS., but the positions of the stars have been corrected by the list of latitudes and longitudes given by Stöffler, whom I have followed, not because he is _correct_, but because he probably represents their positions as they were supposed to be in Chaucer's time very nearly indeed. There was not room to inscribe the names of all the stars on the _Rete_, and to have written them _on the plate below_ would have conveyed a false impression. A list of the stars marked in fig. 2 is given in the note to § 21, l. 4. The Ecliptic is the circle which crosses the Equinoctial at its East and West points (fig. 2). In Chaucer's description of the zodiac, carefully note the distinction between the Zodiac of the Astrolabe and the Zodiac of Heaven. The former is only _six_ degrees broad, and shews only the northern half of the heavenly zodiac, the breadth of which is _imagined_ to be 12 degrees. Chaucer's zodiac only shewed _every other_ degree in the divisions round its border. This border is divided by help of a table of right ascensions of the various degrees of the ecliptic, which is by no means easily done. See Note on l. 4 of this section. I may add that the _Rete_ is also called _Aranea_ or _Volvellum_; in Arabic, _Al´ancab[=u]t_ (the spider).