showing the "very moving of the moon" An introduction to the broader field of "astrologie," a word which at the time referred to the entire span of what we now divide into astrology and astronomy. Part 1 is complete and extant. Part 2 is also extant with certain caveats described below. Part 3, if it ever existed, is not extant as part of the Treatise. Part 4 was, in the opinion of Skeat, probably never written. Part 5 also was probably never written which Skeat approves of. Indeed, he draws attention to Chaucer's comment at the end of conclusion 4: "Natheles these ben observaunces of judicial matere and rytes of payens, in whiche my spirit hath no feith, no knowing of her horoscopum." Part 1 The whole of this section describes the form of an astrolabe. The astrolabe is based on a large plate ("The moder" or "mother") which is arranged to hang vertically from a thumb ring. It has "a large hool, that resceiveth in hir wombe the thin plates". The back of the astrolabe is engraved with various scales (see Skeat's sketch below). Mounted on the back is a sighting rule (Skeat's fig 3, below) "a brod rule, that hath on either end a square plate perced with certein holes". To hold it all together there is a "pyn" with a "littel wegge" (wedge) as shown below at Skeat's fig 7. Into the "womb" various thin plates can be inserted which are designed for a particular place: "compowned after the latitude of Oxenforde". These plates show the star map. Surmounting them is a "riet" or "rete" which is a pierced framework carrying the major stars shown at fig 9. Outside all is another rule, this time not with sighting holes, mounted on the common pivot, see fig 6. Part 2 Part 2 consists of around 40 propositions or descriptions of things that can be done with the astrolabe. The exact number is uncertain since of the later propositions some are of disputed or doubtful authenticity. Skeat accepts that propositions 1-40 are unambiguously genuine. Robinson generally follows Skeat's reasoning. These first 40 propositions form the canon of part 2; the propositions that follow are usually labeled "Supplementary Propositions." The astrolabe The astrolabe was a sophisticated precision instrument. With it one could determine the date, time (when the sky was clear), the position of stars, the passage of the zodiac,