Poet and Son: Lewis Chaucer

By John Harris | May 7, 2013

Lewis, born in 1380, was Geoffrey’s second son, the first being Thomas, born 1367, who was a great man in England by the early fifteenth century. No one knows what happened to Lewis after he grew up, though some records mention him in connection with Thomas.

Thomas had connections through his father, the son of a wealthy wine merchant, and more importantly through his mother, Philippa, who was born into the aristocracy. She was a member of the Queen’s household and then the household of the wife of King Edward III’s powerful brother, John of Gaunt. Thomas seems to have lifted the family even higher. His daughter, Alice Chaucer, the last of Chaucer’s traceable descendents, ended up married to the Earl of Salisbury and then the Duke of Norfolk

Geoffrey likely met Philippa at court. He’d been sent to work as a page at the home of the king’s son, Lionel of Antwerp, and worked his way up in court, serving as a soldier, diplomat, Controller of the Customs of the Port of London, member of parliament for Kent and much else.

When Lewis was ten, Geoffrey gave him an astrolabe and a set of instructions on how to use it that Geoffrey had himself translated into English, since Lewis was too young to know much Latin. The book was by the eighth-century Arab astronomer Messahala, and its Latin version was called Compositio et Operatio Astrolabii (The Structure and Use of Astrolabes).

Astrolabes were invented by the Greeks in the second century BC and developed by the Byzantines and Arabs. They use triangulation to measure the heights of planets and stars from the horizontal. Knowing your latitude, you can tell the time from them (at night); knowing the time, you can calculate your latitude. They were especially useful to mariners who on the open ocean are out of sight of any landmarks. For example, you could hold your course (your latitude) across the Atlantic and hit Cuba, Iceland, Greenland, etc. If you got blown south, the North Star, if that’s what you were sighting on, was closer to the horizon; north and it was further up.


We know from Geoffrey’s poetry that Geoffrey himself was interested in such things. The Canterbury Tales are full of medical and astronomical references that are up to date for their time, and Geoffrey often mentions his sources. He was a great reader.

In introducing his set of instructions, Geoffrey says to Lewis: “Little Lewis my son, I perceive that you have the ability to learn sciences, and I have heard you say often that you want to learn how to use an astrolabe. . . . So I have given you an astrolabe adjusted for our horizon, set to the latitude of Oxenford, and I intend to teach you its use in my little treatise.”

Geoffrey goes on to explain that he has translated the treatise into English, using “naked” (simple) words and basic grammar, “for you don’t know much Latin, my little son.” He actually translates only what a kid could understand, sticking to two parts of the Compositio, the description of the instrument itself and a set of simple problems that can be solved using it.

The treatise begins as follows: “Your astrolabe has a ring to put on the thumb of your right hand when you take the height of things. Note that I will henceforth call this height of a thing its ‘altitude.’ This ring is fastened to the body or ‘mother’ of the astrolabe in such a way that the instrument can hang freely. The mother is a thick plate pierced with a large hole that receives in her womb the thin plates made up for diverse locations. These plates are made in the manner of cobwebs.”

And so it goes. It’s the first scientific or technological report, the first set of instructions for a scientific instrument, in English.




[Poet and Son is a series-in-progress about poets and their offspring.]


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