Трактат Джеффри Чосера об астролябии

Medieval instruction manual on the astrolabe by Geoffrey Chaucer

A Treatise on the Astrolabe is a medieval instruction manual on the astrolabe by Geoffrey Chaucer. It was completed in 1391. It describes both the form and the proper use of the instrument, and stands out as a prose technical work from a writer better known for poetry, written in English rather than the more typical Latin.

The Treatise is considered the "oldest work in English written upon an elaborate scientific instrument". It is admired for its clarity in explaining difficult concepts – although modern readers lacking an actual astrolabe may find the details of the astrolabe difficult to understand. Robinson believes that it indicates that had Chaucer written more freely composed prose it would have been superior to his translations of Boethius and Renaut de Louhans. Chaucer’s exact source is undetermined but most of his ‘conclusions’ go back, directly or indirectly, to Compositio et Operatio Astrolabii, a Latin translation of Messahala's Arabic treatise of the 8th century. His description of the instrument amplifies Messahala’s, and Chaucer’s indebtedness to Messahala was recognised by John Selden and established by Walter William Skeat. Mark Harvey Liddell held Chaucer drew on De Sphaera of John de Sacrobosco for the substance of his astronomical definitions and descriptions, but the non correspondence in language suggests the probable use of an alternative compilation. A collotype facsimile of the second part of the Latin text of Messahala (the portion which is parallel to Chaucer's) is found in Skeat’s Treatise On The Astrolabe. and in Gunther's Chaucer and Messahalla on the Astrolabe. Paul Kunitzsch argued that the treatise on the astrolabe long attributed to Messahala was in fact written by Ibn al Saffar.

Chaucer opens with the words "Lyte Lowys my sone". In the past a question arose whether the Lowys was Chaucer's son or some other child he was in close contact with. Kittredge suggested that it could be Lewis Clifford, a son of a friend and possible a godson of Chaucer's. As evidence he advanced that Lewis Clifford died in October 1391, the year of the composition, which could explain its abandonment. Robinson reports though the finding of a document by Professor Manly "recently" (to 1957) which links one Lewis Chaucer with Geoffrey's eldest child Thomas Chaucer. The likelihood therefore is that the dedication can be taken at face value. Chaucer had an eye to the wider public as well. In the prologue he says:
Now wol I preie mekely every discret persone that redith or herith this litel tretys "

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 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."