Treatise on the Astrolabe

"A Treatise on the Astrolabe" is a medieval essay on the astrolabe by Geoffrey Chaucer. It begins:

:Lyte Lowys my sone, I aperceyve wel by certeyne evydences thyn abilite to lerne sciences touching nombres and proporciouns; and as wel considre I thy besy praier in special to lerne the tretys of the Astrelabie. Than for as moche as a philosofre saith, "he wrappith him in his frend, that condescendith to the rightfulle praiers of his frend," therfore have I yeven the a suffisant Astrolabie as for oure orizonte, compowned after the latitude of Oxenforde; upon which, by mediacioun of this litel tretys, I purpose to teche the a certein nombre of conclusions aperteynyng to the same instrument.

or, in a more modern English form,

:Little Lewis my son, I perceive well by certain evidences your ability to learn sciences pertaining to numbers and proportions; and I am well aware of your constant requests to learn the handling of the Astrolabe. So, as a philosopher says, "He that indulges the reasonable requests of his friend joins himself to that friend", therefore I have given you an astrolabe suitable for our horizons, calibrated to the latitude of Oxford; upon which, by means of this little treatise, I intend to teach you a certain number of conclusions pertaining to the same instrument.

According to the introduction, the work was to have five parts:
#A description of the astrolabe
#A rudimentary course in using the instrument
#Various tables of longitudes, latitudes, declinations, etc.
#A "theorike" (theory) of the motion of the celestial bodies, in particular a table 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.

However, Chaucer only completed parts 1 and 2, plus a small collection of "Supplementary Propositions".

The "Treatise" is considered the oldest work in English describing a complex scientific instrument, and is admired for its clarity in explaining difficult concepts -- although since the astrolabe and related tools are no longer in common use, much of it is difficult for modern readers to understand.

External links

* [http://www.umm.maine.edu/faculty/necastro/chaucer/index.html Chaucer's works in plain-text format (with line numbering). Includes the "Treatise"]
* [http://www.astrolabe.vidmo.net A Treatise on the Astrolabe - a verb database (language analysis, description of the astrolabe and Middle English period)]