A surprise

One of my birthday presents this year was a beautiful book by Christopher de Hamel, Meetings with Remarkable Manuscripts. The author, who is librarian at Corpus Christi College, Cambridge (a library to which he was once refused admission), and in his care are some impressive ancient manuscripts, including a gospel book brought to England by Augustine in the year 597; it is so old that it was produced before Jerome’s Latin Vulgate translation had become standard, and includes some passages from earlier translations.

The book is structured as a sequence of interviews with celebrated manuscripts, as if they were human stars; we meet them in the libraries where they now reside, and are given an impression of their outward appearance before investigating the contents, history, and unexpected connections. The manuscripts include the Book of Kells and an early manuscript of the Carmina Burana.

Reading it, I got quite a surprise. But let me fill in some background first.

The pre-Socratic Greek philosophers where highly inventive and speculative. As well as arguing about whether “everything is change” or “change is impossible”, or whether the world is made out of water or fire or something else, they developed a number of models of the universe. Among these were a geocentric model rather like the one that prevailed until the time of Copernicus, and a heliocentric model (similar to that proposed by Copernicus) put forward by Aristarchus; and also two intermediate models.

One of these, the “Egyptian” system of Herakleides, took into account the fact that Mercury and Venus behave very differently from the other planets, both in their sticking relatively close to the Sun rather than wandering around the whole Zodiacal belt, and in their waxing and waning in brightness as they moved. In hindsight it seems clear that, however the outer planets behave, there is clear evidence that the inner planets go round the Sun. The model proposed by Herakleides involved Mercury and Venus circling the Sun as it (like the other planets) moved round the earth.

A more drastic revision had all the other planets (except the moon) circling the Sun as it moved round the earth: this model was later and perhaps independently proposed by Tycho de Brahe as a way of getting some of the advantages of the Copernican system while not falling foul of those who insist that the earth is fixed.

Then along came Plato, who said that the most perfect form of motion is uniform motion in a circle; and Aristotle, who said that change and decay exist only in the sublunary sphere, and so all the planets must undergo uniform circular motion. This view held sway for more than a millennium and a half.

Or at least, so goes received wisdom. But one of de Hamel’s manuscripts is the Aratea, in the university library in Leiden. It deals with astronomy, with vivid pictures of the constellations, but also includes a “planetarium”, which clearly shows Herakleides’ model with Mercury and Venus circling the Sun.

This manuscript was produced at the court of Charlemagne, in his lifetime or a little after. It is a copy of a manuscript explaining the theories of Aratus of Soli, an astronomer who lived about 300BC, rendered into Latin. The original has not been found; according to de Hamel, a new copy was more important at the time than a possibly battered and damaged original, which could be thrown away once the copy had been made! But this shows clearly that some pre-Socratic Greek knowledge had not been lost by around the year 800. In fact, the planetarium is not part of Aratus’ work, and is probably taken from a calendar from the year 354.

Even more intriguingly, de Hamel cites the work of modern astronomers who have examined this planetarium closely. If we assume that the scribes recorded the actual configuration of planets and stars at the time, and worked to 15 degrees accuracy, the configuration shown occurred on 18 March and 14 April 816, and not again (or before) for 98000 years.

If this is correct, it gives us an astonishingly accurate dating of a mediaeval manuscript. According to a calculation by Bede a little earlier, 18 March was the date on which God created the universe (in the year 3952BCE), so this would be an important anniversary. Charlemagne had died two years earlier, and his son Louis the Pious would be crowned later in the year 816, so the date is plausible historically. There were dramatic developments in education and study in the reign of Charlemagne, driven by Alcuin of York who was his adviser in this early renaissance of classical learning.

Arthur Koestler, from whose book The Sleepwalkers I have taken the account of Greek cosmology, admits that by the year 1000 some of the alternative Greek cosmological manuscripts were being rediscovered; but it seems that this happened earlier, or perhaps in some sense they had never been forgotten. Clearly there are currents here that I am not aware of!