The other side of the plate, called the _front_, and shewn in Fig. 2, had a thick rim with a wide depression in the middle (i. 3). The rim was marked with three rings or circles, of which the outermost was the Circle of Letters (A to Z) representing the twenty-four hours of the day, and the two innermost the degrees of the quadrants (i. 16). The depressed central portion of the plate was marked only with three circles, the 'Tropicus Cancri,' the 'Æquinoctialis,' and the 'Tropicus Capricorni' (i. 17); and with the cross-lines from North to South, and from East to West (i. 15). But several thin plates or discs of metal were provided, which were of such a size as exactly to drop into the depression spoken of. The principal one of these, called the 'Rete,' is shewn in Fig. 2. It consisted of a circular ring marked with the zodiacal signs, subdivided into degrees, with narrow branching limbs both within and without this ring, having smaller branches or tongues terminating in points, each of which denoted the exact position of some well-known star. The names of these stars, as 'Alhabor,' 'Rigel,' &c., are (some of them) written on the branches (i. 21). The 'Rete' being thus, as it were, a skeleton plate, allows the 'Tropicus Cancri,' &c., marked upon the body of the instrument, to be partially seen below it. Another form of the 'Rete' is shewn in Fig. 9, and other _positions_ of the Rete in Fig. 11 and Fig. 12. But it was more usual to interpose between the 'Rete' and the body of the instrument (called the 'Mother') another thin plate or disc, such as that in Fig. 5, so that portions of this latter plate could be seen beneath the skeleton-form of the 'Rete' (i. 17). These plates are called by Chaucer 'tables,' and sometimes an instrument was provided with several of them, differently marked, for use in places having different latitudes. The one in Fig. 5 is suitable for the latitude of Oxford (nearly). The upper part, above the Horizon Obliquus, is marked with circles of altitude (i. 18), crossed by incomplete arcs of azimuth tending to a common centre, the zenith (i. 19). The lower part of the same plate is marked with arcs denoting the twelve planetary hours (i. 20). At the _back_ of the astrolabe revolved the 'rule,' made of metal, and fitted with sights, represented in Fig. 3 (i. 13). At the _front_ of it revolved the 'label,' represented in Fig. 6 (i. 22). All the parts were held together by the central pin (Fig. 4) which passed through the holes in the 'moder,' plates, 'Rete,' rule, and label[59], and was secured by a little wedge (i. 14), which was sometimes fancifully carved to resemble a horse (Fig. 7). Another 'table' or disc is shewn in Fig. 14, and was used for ascertaining the twelve astrological houses. § 29. USES OF THE ASTROLABE PLANISPHERE. I here briefly enumerate such principal uses of the instrument as are mentioned by Chaucer.