Professor Tony Freeth on the history of our understanding of a seemingly improbable device that measures the ingenuity of the astronomers of ancient Greece.
By Dr Shamim Quadir (Senior Communications Officer), Published
On Wednesday 26 November, the School of Science & Technology welcomed Professor Tony Freeth to deliver the annual George Daniels Lecture at City St George’s, University of London.
Professor Freeth’s lecture was introduced by Kenneth Grattan (OBE FREng), George Daniels Professor of Scientific Instrumentation at the School.
Professor Grattan first acknowledged the renowned British Master horologist, Dr George Daniels CBE (1926-2011) . Daniels, an alumnus of the Northampton Institute, City St George’s predecessor institution, is in whose honour the George Daniels Lectures have been held since 2013.
He then spoke on Professor Freeth’s academic background in pure mathematics and mathematical logic, his career as an award-winning documentary filmmaker and his current role as Honorary Professor at the Department of Mechanical Engineering, University College London (UCL).
An ancient shipwreck
In 1901, Greek sponge divers recovered a corroded lump from an ancient shipwreck near the tiny island of Antikythera, between Crete and mainland Greece. It subsequently split apart and revealed tiny precision gearwheels — a shocking discovery for ancient Greece.
More than a century later, we know that the Antikythera mechanism was a highly sophisticated astronomical calculating machine, constructed from bronze gearwheels.
In his lecture, Professor Freeth took his audience on a fascinating journey through the breakthroughs that have increased our knowledge of the mechanism to date, using a blend of both technical lecture and narration of documentary footage from his productions on the subject.
Professor Freeth shared the vital contributions of experts over the years to uncover some of the Antikythera mechanism’s astounding feats of astronomical measurement. Also revealing the comprehensive knowledge of astronomers of Ancient Greece: of the movements of the sun, moon, and potentially of planets.
Highlights: George Daniels Lecture 2025
He stressed both what these experts got right about the Antikythera mechanism, but almost inevitably what they also got wrong. Nevertheless, setting a higher platform upon which future researchers could help solve its remaining riddles, and reveal its remaining secrets.
Professor Freeth shared that the first real breakthrough in understanding both the mechanism’s purpose and workings came from the German philologist (language expert) Albert Rehm between 1905 and 1906.
Working with the major recovered fragments of the mechanism, he transcribed ancient Greek inscriptions which identified a Star Calendar, known as a ‘parapegma’ in the ancient world. He further found three ancient astronomical cycles named and outlined: the Callippic Cycle – 76 years, the Metonic Cycle – 19 years and the Saros Cycle – 223 months. All cycles key to tracking how the sun and the moon move to predict lunar eclipses. Rehm correctly deduced the mechanism could measure elliptical (oval) shaped orbits and he produced a model of what the fully assembled mechanism might look like, which was an important step - but largely wrong.
A resumed interest
Investigations into the mechanism lapsed until British science historian, Professor Derek J de Solla Price began his in 1951 and identified the remains of 20 bronze gears, estimating the number of teeth on the gears to understand the mechanism better. In 1959 he published an article in Scientific American which illustrated his understanding at the time – with later investigation finding 17 out of his gear tooth counts were wrong.
However, Price went on to x-ray the mechanism in 1970 with physicist, Charambalos Karakalos, with Karakalos and his wife Emily counting the gear teeth from the x-rays. This resulted in a much-improved model, which appeared in Price’s report, ‘Gears of the Greeks’ in 1974.
While Price’s 1974 model was still wrong, Professor Freeth recounted that what it did get right was the ‘Metonic gear train’ which was a major breakthrough. While Rehm had previously found inscriptions of the 19-year Metonic Cycle, Price had shown a representation of this cycle within the bronze gears of the mechanism. For example, the 254 ‘sidereal months’ (where the moon passes through the entire zodiac of stars 254 times in the 19-year Metonic Cycle) represented in the number gear teeth and ratio of gears themselves.
Questions and networking on the night
Professor Freeth shared the Antikythera mechanism investigations of Michael Wright, formerly a curator of Mechanical Engineering at the London Science Museum, who he deemed the next great pioneer of research in the field, and who quite literally took a much more hands on approach.
(From a new x-ray approach he helped develop, Wright had studied new images of the mechanism) and consequently advanced a number of new proposals within a working model of it he created himself. Housed in a wooden box, as was the original, it comprised a main front face with dials, and also a back face too, with further dials illustrating astronomical measurement. Professor Freeth outlined the construction of this model, as well as the theory behind its internal mechanisms and the advances it made upon Price’s model.
High quality evidence
He later moved on to talk about his own research into the Antikythera Mechanism between 2000-2005, which followed his frustration with the lack of good evidence to work with from the mechanism. It involved transporting a new x-ray computed tomography (CT) machine from the UK to Greece to study of all 82 fragments of the mechanism, which included new ones found.
This new x-ray CT imaging provided spectacularly clear visualisation of gears, plates, pins, shafts, and spacers within the mechanism in fine 3D detail, and revealed new ancient Greek inscriptions which were crucial to his team’s own construction of a new model.
From this, Professor Freeth was able to identify a lunar eclipse prediction system within the Antikythera Mechanism, appearing as a spiral dial on its back face. He was finally able to solve what had previously appeared to him to be a redundant use of a 53-tooth gear, which itself is a strange number of teeth for a gear wheel to have.
However, this number of teeth was found to be required with other newly revealed mechanisms to account for a subtle change in the moon’s orbit of the earth which happens every nine years. While the ancient Greeks are known to be aware of this movement of the moon, what astonished Freeth is that the mechanism’s designers used a combination of a pin and slot mechanism mounted on ‘epicyclic’ gearing to create the variation of rotation to account for this. He remarked:
Professor Freeth used the final part of his lecture to revisit the work of Michael Wright, but this time highlighting Wright’s theory of there being an additional element to the mechanism’s gearing that modelled the motion of the five known planets to the ancient Greeks (Mars, Venus, Mercury, Jupiter and Saturn).
He shared how a new team he is part of at UCL is combining the evidence from still photographs, x-ray CT imaging and surface imaging with a host of reconstruction principles to fill in the gaps in their knowledge to build their current model of the Anthikyeria mechanism, which includes a prediction of the motion of the five planets which fits with the evidence.
Professor Freeth ended his lecture by quoting the late theoretical physicist, Professor Richard Feynmann, from a letter written in June 1980 to his wife and daughter after seeing the Antikythera Mechanism first-hand, saying: