One of the more unusual features of the magnificent St Mary’s Church in Ottery St Mary is the ancient astronomical clock. Not only does it tell the time, it also shows the age and phase of the moon, and it has done so for more than five centuries. This beautiful clock is a rare example of medieval craftsmanship and gives us a unique insight into life many centuries ago.
Perhaps there is a chiming clock in the town where you live that insists on telling you the hour. You probably also wear a wristwatch and, failing that, your computer or phone provides minute by minute updates of the time. But it hasn’t always been like this, so how were clocks developed and how did time come to rule us?
The earliest clocks
In Western Europe, the first rudimentary clocks began to appear only during the medieval era. They were the preserve of monasteries and their purpose was to provide a signal to the sacristan who then rang the cloister bell, calling the monks to prayer at regular intervals. These simple timepieces were probably water clocks, where time was measured via the flow of water in to or out of a vessel. Although they were not very accurate, they were a great improvement on sundials in a cloud-prone country.
Then, in the late 13th and early 14th centuries, a major breakthrough in clock development occurred. Reports of new mechanical clocks began to appear from various places in Europe including Exeter (1284) and Salisbury (1306) and, most likely, this coincided with the invention of the escapement. These new clocks would probably have been driven by a weight attached to a rope wound round a drive shaft. The escapement was a device that enabled the weight to descend in a stepwise manner, each step representing the passing of time which could be displayed on the clock face. The familiar “tick, tock” of these clocks is the sound of the escapement. So began a new era of mechanical clocks composed solely of metal wheels and gears. These clocks were enthusiastically installed in church towers and other public buildings allowing a bell to be rung at intervals throughout the day, broadcasting time to the inhabitants of the town and, for example, signalling the opening of trading at the market.
As these mechanical clocks became more sophisticated they were elaborated to show not only time but also the age and phase of the moon. The south west of England has four well preserved examples of these ancient astronomical clocks that have survived for at least five centuries, perhaps because of their novelty or their beauty. They are to be found in Exeter Cathedral, Wells Cathedral, Wimborne Minster and in Ottery St Mary Church.
The Astronomical Clock in St Mary’s Church,
Ottery St Mary
The clock hangs high above the south transept and below the bell tower. Its bright blue face, about a metre and a half square, is liberally decorated with gold and red and topped with a gold angel blowing a trumpet. Unashamedly beautiful and garish at the same time, it dominates the scene.
The clock has two circular dials. The outer dial shows the hour with two sets of twelve Roman numerals. A golden sphere, representing the sun, moves to show the time. The inner dial contains thirty Arabic numerals with a gold star moving between them to show the age of the moon. Within the inner dial is a sphere painted half white, half black which rotates on its axis once every 29.5 days depicting the moon and its phases; the moon sphere also moves around the dial once every 24 hours. A black sphere at the centre of the clock shows the earth as the centre of the universe. The clock mechanism is visible behind the face.
The exact age of the clock is not known but we may get a hint from the strong similarity between the Ottery St Mary clock and the astronomical clock in Exeter Cathedral, which dates from the 15th century. Also, both timepieces depict a medieval view of the structure of the universe where the sun rotates about the earth. This model was only superseded in 1543 when Copernicus proposed that the earth actually rotates about the sun, so we can be fairly sure that both are older than this date.
Why astronomical clocks?
It is easy to understand the purpose of a clock that broadcasts the time of day to a busy town but why would the medieval clockmaker go to the trouble to include information about the age and phase of the moon and the apparent movement of the sun about the earth? One possibility may have been a desire of the contemporary Church to create a model of God’s celestial universe but perhaps there were secular reasons as well. For example, knowledge of the phases of the moon would have been useful in planning a long journey at night or a meeting in winter. Also, because of the influence of the moon on tides, knowledge of the state of the moon would have been useful for seafarers.
When they first appeared, these clocks must have seemed miraculous: man had constructed a machine that would predict the motion of the sun and moon and show the hours of the day. Possession of such a clock would have been a source of civic and ecclesiastical pride and conferred distinction on a town. For Ottery St Mary, perhaps it was considered fitting to install such a clock in its “mini-cathedral” of St Mary’s church.
The 21st century observer, surrounded by technology and gadgets, might, however, simply view the Ottery St Mary clock as an ancient curiosity. This would be a mistake: the clock is a rare example of advanced medieval craftsmanship as well as offering considerable insight into how life was lived so many years ago. It is a true medieval marvel.