5. Over-thwart this for-seide longe lyne, ther crosseth him another lyne of the same lengthe from est to west. Of the whiche lyne, from a litel croys + in the bordure un-to the centre of the large hole, is cleped the Est lyne, or elles the lyne Orientale; and the remenant of this lyne fro the forseide + un-to the bordure, 5 is cleped the West lyne, or the lyne Occidentale. Now hastow here the foure quarters of thin Astrolabie, devyded after the foure principals plages or quarters of the firmament. And for the more declaracioun, lo here thy figure.

6. The est side of thyn Astrolabie is cleped the right side, and the west side is cleped the left side. Forget nat this, litel Lowis. Put the ring of thyn Astrolabie upon the thoumbe of thy right hand, and thanne wole his right syde be toward thy left syde, and his left syde wol be toward thy right syde; tak this rewle general, 5 as wel on the bak as on the wombe-side. Upon the ende of this est lyne, as I first seide, is marked a litel +, wher-as evere-mo generaly is considered the entring of the first degree in which the sonne aryseth. And for the more declaracioun, lo here the figure.

7. Fro this litel + up to the ende of the lyne meridional, under the ring, shaltow finden the bordure devyded with 90 degrees; and by that same proporcioun is every quarter of thin Astrolabie devyded. Over the whiche degrees ther ben noumbres of augrim, that devyden thilke same degrees fro fyve to fyve, as sheweth by 5 longe strykes by-twene. Of whiche longe strykes the space bytwene contienith a mile-wey. And every degree of the bordure contieneth foure minutes, that is to seyn, minutes of an houre. And for more declaracioun, lo here the figure.

8. Under the compas of thilke degrees ben writen the names of the Twelve Signes, as Aries, Taurus, Gemini, Cancer, Leo, Virgo,

5. The Est lyne is marked with the word Oriens; the West lyne, with Occidens.

6. The rule is the same as in heraldry, the right or dexter side being towards the spectator's left.

7. As the 360 degrees answer to 24 hours of time, 15° answer to an hour, and 5° to twenty minutes, or a Mile-way, as it is the average time for walking a mile. So also 1o answers to 4 minutes of time. See the two outermost circles in fig. 1, and the divisions of the 'border' in fig. 2.

8. See the third and fourth circles (reckoning inwards) in fig. 1.

10

Libra, Scorpio, Sagittarius, Capricornus, Aquarius, Pisces; and the nombres of the degrees of tho signes ben writen in augrim 5 above, and with longe devisiouns, fro fyve to fyve; devyded fro tyme that the signe entreth un-to the laste ende, But understond wel, that thise degrees of signes ben everich of hem considered of 60 minutes, and every minute of 60 secondes, and so forth in-to smale fraccions infinit, as seith Alkabucius. And 10 ther-for, know wel, that a degree of the bordure contieneth foure minutes, and a degree of a signe contieneth 60 minutes, and have this in minde. And for the more declaracioun, lo here

thy figure.

9. Next this folweth the Cercle of the Dayes, that ben figured in maner of degrees, that contienen in noumbre 365; divyded also with longe strykes fro fyve to fyve, and the nombres in augrim writen under that cercle. And for more declaracioun, lo 5 here thy figure.

10. Next the Cercle of the Dayes, folweth the Cercle of the names of the Monthes; that is to seyen, Ianuare, Februare, Marcius, Aprile, Mayus, Iuin, Iulius, Augustus, Septembre, October, Novembre, Decembre. The names of thise monthes 5 were cleped in Arabiens, somme for hir propretees, and some by statutz of lordes, some by other lordes of Rome. Eek of thise monthes, as lyked to Iulius Cesar and to Cesar Augustus, some were compowned of diverse nombres of dayes, as Iuil and August. Thanne hath Ianuare 31 dayes, Februare 28, March 10 31, Aprille 30, May 31, Iunius 30, Iulius 31, Augustus 31, September 30, Octobre 31, Novembre 30, December 31. Natheles, al-though that Iulius Cesar took 2 dayes out of Feverer and put hem in his moneth of Iuille, and Augustus Cesar cleped the moneth of August after his name, and ordeyned it of 31 dayes,

9. See the fifth and sixth circles in fig. 1.

10. See the seventh, eighth, and ninth circles in fig. 1. The names of the months are all Roman. The month formerly called Quinctilis was first called Julius in B. C. 44; that called Sextilis was named Augustus in B. C. 27. It is a mistake to say that Julius and Augustus made the alterations spoken of in the text; what Julius Cæsar really did, was to add 2 days to the months of January, August (Sextilis), and December, and I day to April, June, September, and November. February never had more than 28 days till he introduced bissextile years.

yit truste wel, that the sonne dwelleth ther-for nevere the more ne 15 lesse in oon signe than in another.

11. Than folwen the names of the Halidayes in the Kalender, and next hem the lettres of the Abc. on which they fallen. And for the more declaracioun, lo here thy figure.

12. Next the forseide Cercle of the Abc., under the cros-lyne, is marked the scale, in maner of two squyres, or elles in manere of laddres, that serveth by hise 12 poyntes and his devisiouns of ful many a subtil conclusioun. Of this forseide scale, fro the croos-lyne un-to the verre angle, is cleped umbra versa, and the 5 nether partie is cleped the umbra recta, or elles umbra extensa. And for the more declaracioun, lo here the figure.

13. Thanne hastow a brood Rewle, that hath on either ende a square plate perced with a certein holes, some more and some lesse, to resseyven the stremes of the sonne by day, and eek by mediacioun of thyn eye, to knowe the altitude of sterres by nighte. And for the more declaracioun, lo here thy figure.

14. Thanne is ther a large Pyn, in maner of an extree, that

11. See the two inmost circles in fig. 1. The names given are adopted from a comparison of the figures in the Cambridge University and Trinity MSS., neither of which are quite correct. The letters of the 'Abc.' are what we now call the Sunday letters. The festivals marked are those of St. Paul (Jan. 25), The Purification (Feb. 2), The Annunciation (Mar. 25), The Invention of the Holy Cross (May 3), St. John the Baptist (June 24), St. James (July 25), St. Lawrence (Aug. 10), The Nativity of the Blessed Virgin (Sept. 8), St. Luke (Oct. 18), St. Martin of Tours (Nov. 11), and St. Thomas (Dec. 21).

12. The 'scale' is in Latin Quadrans, or Scala Altimetra. It is certain that Chaucer has here made a slip, which cannot be fairly laid to the charge of the scribes, as the MSS. agree in transposing versa and recta. The side-parts of the scale are called Umbra versa, the lower part Umbra recta or extensa. This will appear more clearly at the end of Part II. (I here give a corrected text.)

13. See fig. 3, Plate III. Each plate turns on a hinge, just like the 'sights' of a gun. One is drawn flat down, the other partly elevated. Each plate (tabella vel pinnula) has two holes, the smaller one being the lower. This Rewle is named in Arabic Alhidada or Alidāda; in Latin Verticulum, from its turning easily on the centre; in Greek Dioptra, as carrying the sights. The straight edge, passing through the centre, is called the Linea Fiducia. It is pierced by a hole in the centre, of the same size as that in the Mother.

14. See fig. 4, Plate III. The Pin is also called Axis or Clavus, in

5

goth thorow the hole that halt the tables of the clymates and the riet in the wombe of the Moder, thorw which Pyn ther goth a litel wegge which that is cleped the hors,' that streyneth alle 5 thise parties to-hepe; this forseide grete Pyn, in maner of an extree, is imagined to be the Pol Artik in thyn Astrolabie. And for the more declaracioun, lo here the figure.

15. The wombe-side of thyn Astrolabie is also devyded with a longe croys in foure quarters from est to west, fro south to north, fro right syde to left syde, as is the bak-syde. And for the more declaracioun, lo here thy figure.

16. The bordure of which wombe-side is devyded fro the poynt of the est lyne un-to the poynt of the south lyne under the ring, in 90 degres; and by that same proporcioun is every quarter devyded as is the bak-syde, that amonteth 360 degrees. And 5 understond wel, that degrees of this bordure ben answering and consentrik to the degrees of the Equinoxial, that is devyded in the same nombre as every othere cercle is in the heye hevene. This same bordure is devyded also with 23 lettres capitals and a smal croys + above the south lyne, that sheweth the 24 houres 10 equals of the clokke; and, as I have said, 5 of thise degrees maken a mile-wey, and 3 mile-wey maken an houre. And every degree of this bordure conteneth 4 minutes, and every minut 60 secoundes; now have I told thee twye. And for the more declaracioun, lo here the figure.

17. The plate under thy riet is descryved with 3 principal

Latin-Arabic Alchitot; it occupies the position of the Arctic or North Pole, passing through the centre of the plates that are required to turn round it. The Wedge is called cuneus, or equus restringens, in Arabic Alfaras or the horse, because it was sometimes cut into the shape of a horse, as shewn in fig. 7, Plate IV, which is copied from MS. Univ. Camb. Ii. 3. 3.

15. See fig. 2, Plate II. In the figure, the cross-lines are partly hidden by the Rete, which is separate and removable, and revolves within the border.

16. The Border was also called Margilabrum, Margolabrum, or Limbus. It is marked (as explained) with hour-letters and degrees. Each degree contains 4 minutes of time, and each of these minutes contains 60 seconds of time.

17. We may place under the Rete any plates we please. If only the Mother be under it, without any plate, we may suppose the Mother marked as in fig. 2. The plate or disc (tympanum) which was usually

cercles; of whiche the leste is cleped the cercle of Cancer, by. cause that the heved of Cancer turneth evermor consentrik up-on the same cercle. In this heved of Cancer is the grettest declinacioun northward of the sonne. And ther-for is he cleped the 5 Solsticioun of Somer; whiche declinacioun, aftur Ptholome, is 23 degrees and 50 minutes, as wel in Cancer as in Capricorne. This signe of Cancre is cleped the Tropik of Somer, of tropos, that is to seyn 'agaynward;' for thanne by-ginneth the sonne to passe fro us-ward. And for the more declaracioun, lo here the figure.

ΙΟ

The middel cercle in wydnesse, of thise 3, is cleped the Cercle Equinoxial; up-on whiche turneth evermo the hedes of Aries and Libra. And understond wel, that evermo this Cercle Equinoxial turneth iustly fro verrey est to verrey west; as I have shewed thee in the spere solide. This same cercle is cleped also the Weyere, 15 equator, of the day; for whan the sonne is in the hevedes of Aries and Libra, than ben the dayes and the nightes ilyke of lengthe in al the world. And ther-fore ben thise two signes called the Equinoxies. And alle that moeveth with-in the hevedes of thise Aries and Libra, his moeving is cleped north- 20 ward; and alle that moeveth with-oute thise hevedes, his moeving

dropped in under the Rete is that shewn in fig. 5, Plate III, and which Chaucer now describes. Any number of these, marked differently for different latitudes, could be provided for the Astrolabe. The greatest declination of the sun measures the obliquity of the ecliptic, the true value of which is slightly variable, but was about 23° 31′ in Chaucer's time, and about 23° 40′ in the time of Ptolemy, who certainly assigns to it too large a value. The value of it must be known before the three circles can be drawn. The method of finding their relative magnitudes is very simple. Let ABCD (fig. 8, Pl. IV) be the tropic of Capricorn, BO the South line, OC the West line. Make the angle EOB equal to the obliquity (say 231°), and join EA, meeting BO in F. Then OF is the radius of the Equatorial circle, and if GH be drawn parallel to EF, OH is the radius of the Tropic of Cancer. In the phrase angulus primi motus, angulus must be taken to mean angular motion. The 'first moving' (primus motus) has its name of 'moving' (motus) from its denoting motion due to the primum mobile or first moveable.' This primum mobile (usually considered as the ninth sphere) causes the rotation of the eighth sphere, or sphæra stellarum fixarum. See the fig. in MS. Camb. Univ. Ii. 3. 3 (copied in fig. 10, Pl. V). Some authors make 12 heavens, viz. those of the 7 planets, the firmamentum (stellarum fixarum), the nonum cœlum, decimum cœlum, primum mobile, and cælum empyræum.