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 spelling,


 * Little Lewis my son, I perceive well by certain evidences thine ability to learn sciences touching numbers and proportions; and as well consider I thy constant prayer in special to learn the treatise of the Astrolabe. Than for as much as a philosopher saith, "He wrappth him in his friend, that condescendth to the rightful prayers of his friend", therefore have I given thee a suffisant Astrolabe as for our horizons, compounded after latitude of Oxford; upon which, by means of this little treatise, I purpose to teach thee a certain number of conclusions pertaining to the same instrument.

According to the introduction, the work was to have five parts:
 * 1) A description of the astrolabe
 * 2) A rudimentary course in using the instrument
 * 3) Various tables of longitudes, latitudes, declinations, etc.
 * 4) A "theorike" (theory) of the motion of the celestial bodies, in particular a table showing the "very moving of the moon"
 * 5) 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.

The stars listed on the rim of the rete of the drawings in the Treatise are given below with their modern names:

Reerences

 * Edgar Laird. "Astrolabes and the Construction of Time in the Late Middle Ages." In: Constructions of Time in the Late Middle Ages. Ed. Carol Poster and Richard Utz. Evanston, IL: Northwestern University Press, 1997. Pp. 51-69.
 * J. D. North. Chaucer's Universe (Oxford: Clarendon, 1988).