a Treatise on the Astrolabe

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Geoffery Chaucer instructs the boy Lewis -- his son, or the son of a friend -- in the use of the astronomical instrument the Astrolabe, for measuring the angle between the horizon and an object in the sky. The astrolabe, which preceded the sextant, is an invention of the Arabs.

"A treatise on the Astrolabe," from The works of Geoffery Chaucer, published in Hammersmith by Kelmscott Press, 1896. From University Libraries (the Fine and Rare Book Rooms and the Architecture Archives) of Carnegie Mellon University, Pittsburgh, Pennsylvania USA.

Jim Olson, the former Mariner Cadet, gifted me with his second-best student sextant. It kicks ass. Don't need no steenkin batteries. If the electricity goes out in your lifeboat, you can still figure out your Latitude and (if your watch is accurate) your Longitude.

a Sextant & an Accurate Clock:
Don't venture onto the Sea without them.

~ ~ ~

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 mochel as a philosofre saith, "he wrappith him in his frend, that condescendith to the rightfulle praiers of his frend," therfore have I 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. I seie a certein of conclusions, for thre causes. The first cause is this: truste wel that alle the conclusions that han be founde, or ellys possibly might be founde in so noble an instrument as is an Astrelabie ben unknowe parfitly to eny mortal man in this regioun, as I suppose. An-other cause is this, that sothly in any tretis of the Astrelabie that I have seyn there be somme conclusions that wol not in alle thinges parformen her bihestes; and somme of hem ben to harde to thy tendir age of ten yeer to conceyve.