John Westwyk – the genius who invented a computer 627 years ago

This is the story of a man who 627 years ago designed a machine (a computer), six feet across, of polished wood and brass, that could find the position of the planets or predict it for any year. Explaining his life’s work makes a bigger point: that Edward Gibbon’s phrase the “darkness of the Middle Ages” was misconceived, even with regard to experimental science.

It seems to me that Gibbon’s attitude still prevails and most people think the medieval world-view foolishly muddled. Before diving in to Seb Falk’s counter-narrative, focusing on astronomy, it might be worth trying out this brief thought experiment. We speak of the Sun rising and setting, but we say that it just looks as though the Sun goes around the Earth. Really, we say, the Earth goes around the Sun. Yet the explanation of the Sun’s apparent rising and setting is not, as many unthinkingly say, that the Earth goes around the Sun. That takes a year. The explanation is that the Earth spins on its axis.

I suggest that we need to jettison a snobbish assumption of present-day superiority of intellect if we are to understand the scientific theories of the Middle Ages. I was a little disappointed that Seb Falk took the High Middle Ages, the 14th century, as his period, rather than earlier centuries, around the life of Charlemagne (AD 800) or Alfred the Great (900), with darker reputations but just as much light in reality.

But astronomy, a science in which medieval thinkers excelled, is a good vehicle (if we can keep up with the geometry) to explain the arithmetic, map-making or medicine that went with it. If anyone can make it clear, it is Seb Falk, a Cambridge historian, with his carefully constructed narrative and prose as plain as a well-forged “label”, or rotating pointer on an astrolabe.

His hero John Westwyk took his name from a manor near the Roman ruins of Verulamium and became a monk at St Albans Abbey, a place of learning with established relations with the monarch. Later he transferred to the monastery at Tynemouth and, more surprisingly, in 1383 went on crusade, getting no further than Ypres. A decade later, in his own hand in a manuscript that was for a time attributed to Chaucer, John Westwyk left the construction plans and user manual for the equatorium, his wheel-upon-wheel machine. In 1955 a nice edition in green cloth was published by Cambridge University Press under the title The Equatorie of the Planetis. A little-thumbed copy sits on a shelf at home.

It was edited by a brilliant maverick scholar, Derek Price, who had discovered the manuscript unregarded at Peterhouse, Cambridge. It attracted interest because of two words written in a margin: radix Chaucer. Radix was a technical term for a baseline data set in astronomy. The attribution to Chaucer was not foolish, for the poet had written his own Treatise on the Astrolabe for a 10-year-old child. It was a Norwegian scholar, Kari Anne Rand, who looked through manuscripts methodically until in 2014 she announced she found one with handwriting identical with that of the Equatorie. It was in a book given by St Albans Abbey to Tynemouth, and the dedication contained the name “Dompnus Johannes de Westwyke”.

Using the obscure Westwyk as a guide allows Falk to present the world of his time without overshadowing it with a more famous figure like Chaucer. In preparation for the task of our appreciating the solid geometry used in modelling the solar system, Falk lets the reader limber up with a method for using the joints of the fingers to add or subtract large numbers up to 9,999. A diagram is given from a manuscript by Bede (died AD 735).

A couple of pages on, Falk gives a simple method for long division in your head of, say, 729 by 34. It works just as well if the numbers are written in Roman numerals (DCCXXIX ÷ XXXIV).

This was child’s play for Westwyk, who in his astronomical calculations used sexagesimal units, based on sixties. We do the same thing every day to number the hours in minutes and seconds. Westwyk, in tables expressing sums with great precision, would go as far as dividing by 60 nine times, to express, for example, a 98,000-million-millionth part of a complete circle. Such numbers were needed when calculating the slow eastward drift from year to year of the constellations against the conceptual framework of the night sky (which, it was known, would take 49,000 years to complete a circuit). Westwyk and his contemporaries were prepared to deal with even slower celestial movements that would take 750 billion years to go through one degree of the 360 degrees in a circle.

What, you may still ask, was the purpose of being so precise if everyone erroneously thought the Sun went around the Earth? Isn’t it straining at a gnat while swallowing a camel? But one thing I did learn from Derek Price’s introduction to the Equatorie is that when discussing relative motion it doesn’t matter whether you take the Earth as stationary or the Sun.

The heliocentric model proposed by Copernicus in 1543, Falk judges, “in the end, was no simpler than the one it replaced”. Copernicus had wanted to iron out apparent irregularities in the system inherited from Ptolemy, in which the Earth wasn’t quite at the centre of the apparent motion of the Sun and planets, each of which went around its own so-called “deferent centre”, a little offset from the Earth. Westwyk knew all about that – he advises marking the deferent centre with a “little hole that is no wider than a small needle”.

It is notable that he wrote (as Chaucer did in his Astrolabe) in vernacular English. Newton, 300 years later, in the Principia Mathematica, was still writing in Latin, the international language of learning. Westwyk’s mental world was just as international but he spanned it using several languages (relying on translators for Arabic sources).

Even so, a real surprise is to find that the first words of the Equatorie are: “In the name of God, pitos [compassionate] and merciable [merciful]”. This is none other than the Bismillah, the Islamic invocation that begins the Koran. It says nothing contrary to Christian belief, but here demonstrates, more strongly than if a British political tract were to begin, “Liberty, equality, fraternity”, the extent of 14th-century trans-cultural influence.

“Belief in God never prevented people from seeking to understand the world around them,” Falk says. Again and again he traces borrowings by Western Christian astronomers from Muslim astronomers. The up-to-date astronomical tables in the 1320s were translated into Latin in Paris from the Castilian that two Jewish astronomers had used when presenting their work to King Alfonso the Wise. Copernicus was still using them two centuries later.

As for the equatorium, it was at last built. The Whipple Museum of the History of Science, Cambridge, keeps a six-foot exemplar, made under Derek Price’s instructions in the workshop that later produced Crick and Watson’s model of DNA. The huge instrument, its use and origin so soon forgotten, had been put in store in a box marked “King Arthur’s Table”. But now there is a website hosted by Peterhouse on which you can use it virtually to compute the position of Venus, say, on Thursday February 17 3102 BC (to which historians once assigned Noah’s Flood) or the position of Mars on your birthday.

The Light Ages: A Medieval Journey of Discovery is published by Allen Lane at ￡20. To order your copy for ￡16.99, call 0844 871 1514or visit the Telegraph Bookshop