A Treatise on the Astrolabe is a medieval essay on the astrolabe by 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 modern English,

Little Lewis my son, certain evidence enables me to well perceive your ability to learn the sciences, including numbers and proportions; and I have also heard your constant requests to learn of the astrolabe in particular. And, since the philosophers say "He who grants the reasonable requests of his friend joins himself to that friend", I have given you an astrolabe designed for our horizons and calibrated to the latitude of Oxford; with which, according to the information in this little treatise, I propose to teach you a certain number of conclusions appertaining to the 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

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 link

• Chaucer's works in plain-text format (with line numbering). Includes the Treatise