Treatise on the Astrolabe

A Treatise on the Astrolabe is a medieval instruction manual on the astrolabe by Geoffrey Chaucer. It is notable for being written in prose, in English and for describing a scientific instrument.

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 Boece and Melibee.

The work is written in free flowing contemporary (1391) English, today commonly referred to as middle English. Chaucer explains this departure from the norm thus:

Chaucer proceeds to labour the point somewhat:

He continues to explain that it easier for a child to understand things in his own language than struggle with unfamiliar grammar, a commonplace idea today but radical in the fourteenth century. Finally, he appeals to Royalty (his wife was a lady-in-waiting to Edward III's queen and sister to John of Gaunt's wife) in an early version of the phrase "the King's English":

Skeat identifies 22 manuscripts of varying quality. The best he labels A, B and C which are MS. Dd. 3.53 (part 2) in the Cambridge University Library, MS. E Museo 54 in the Bodleian Library and MS. Rawlinson, Misc. 1262 also in the Bodleian.A and B were apparently written by the same scribe, but A has been corrected by another hand. Skeat observes that the errors are just those described in "Chaucers Wordes unto Adam, His Owne Scriveyn":

A has indeed been rubbed and scraped then corrected by another hand. This latter scribe Skeat believes to be a better writer than the first. To this second writer was the insertion of diagrams entrusted.A and B were apparently written in London about the year 1400, that is some 9 years after the original composition. Manuscript C is also early, perhaps 1420 and closely agrees with A.

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