1266. Read I n' can; see note to A. 764.
1273. 'The astronomical tables, composed by order of Alphonso X, king of Castile, about the middle of the thirteenth century, were called sometimes Tabulae Toletanae, from their being adapted to the city of Toledo. There is a very elegant copy of them in MS. Harl. 3647.'—T.
In Chaucer's Astrolabe, ii. 44. 16, we find:—'And if hit so be that hit [i. e. the time for which the change in a planet's position is being reckoned] passe 20 [years], consider wel that fro 1 to 20 ben anni expansi, and fro 20 to 3,000 ben anni collecti.' The changes in position of the various planets were obtained from these tables. The quantities denoting the amount of a planet's motion during round periods of years, such as twenty, forty, or sixty years, were entered in a table headed Anni collecti. Similar quantities for lesser periods, from one year up to twenty years, were entered under the headings 1, 2, 3, &c.; and such years were called Anni expansi, i. e. single or separate years. See Ptolemy's Almagest, lib. vi. and lib. ix.; and the note in vol. iii. p. 367.
1276. rotes, roots. The 'root' is the tabulated quantity belonging to a given fixed date or era, from which corresponding quantities can be calculated by addition or subtraction. Thus the longitude of a planet at a given date is the 'root'; and its longitude at another date, say twenty-three years later, can be obtained from the Toletan tables by adding (1) its change of longitude in twenty years, as given in the table of Anni collecti, and (2) its further change in three years, as given in the table of Anni expansi. Chaucer uses the term 'root' again in B. 314; and in his Astrolabe, ii. 44. 1; q.v.
1277. 'Centre' was a technical name for the end of the small brass projection on the 'rete' of an astrolabe which denoted the position of a fixed star (usually of the first magnitude). See Chaucer's Astrolabe, Fig. 2 (in vol. iii.); and Centre in the Glossary. 'Argument' is an astronomical term still in use, and means 'the angle, arc, or other mathematical quantity, from which another required quantity may be deduced, or on which its calculation depends'; New Eng. Dictionary.
In Chaucer's Astrolabe, § 44 of Part II. is headed—'Another maner conclusion, to knowe the mene mote and the argumentis of any planete.'
1278. proporcionels convenients, fitting proportionals; referring to a table of 'proportional parts,' by which fractional parts of a year can be taken into consideration, in calculating the motions of the planets.
1279. equacions, equations; probably here used in the sense of 'exact quantities.' Thus the 'exact quantity' of a planet's motion, during a given time, can be obtained by adding together the motion during the 'collect' years, the 'expanse' years, and the fraction of a year; see the last note.
1280. eighte spere, eighth sphere; cf. 'ninthe speere' in l. 1283. In the old astronomy (as explained more fully in the note to B. 295), there were nine imaginary spheres, viz. the seven spheres of the seven planets, the eighth sphere or sphere of fixed stars (supposed to have a slow motion from west to east about the poles of the zodiac, to account for the precession of the equinoxes), and the ninth sphere or primum mobile, which had a diurnal motion from east to west, and carried
everything with it. Alnath is still a name for the bright star α Arietis, of the first magnitude, which was necessarily situate in the eighth sphere. But the head of the fixed Aries, or the true equinoctial point, was in the ninth sphere above it.