All Saint's Church Clock

Article written by Dr Chris Thomas, November 2018

Introduction

I grabbed the ancient six inch nail gratefully and heaved myself through the hatch, away from the top of the 30 foot steep ladder, steadied by John Uttin. I could hear the ticking of the clock but my eyes had to grow accustomed to the dark before the outline of the mechanism gradually became visible. I’d lived in Milton for over 30 years, but it took a planned talk on ‘A Briefer History of Time’ to finally get me to this long awaited moment. In the weeks that followed I learnt more about the history of our church clock, reaching back millennia before its installation in 1848.

The Clock, Then and Now

The clock at All Saints Milton was installed in 1848, paid for largely by money received from the Great Eastern Railway, as compensation for parish land acquired for the railway line that now hurries past Milton en-route from Cambridge to Ely. It was made in the traditional ‘Birdcage’ design. Basically, a large box like metal frame has a number of supporting vertical bars that hold rods with gears. The gears on the left half of the birdcage drive the clock. The gears on the right hand side drive the hourly chime. There were originally two sets of weights to provide power to each set of gears, with the larger weights needed to power the hammer that would strike the bell. The weights would have to be cranked up again from the tower to keep the clock running. The large weights were replaced with two electric motors that would automatically wind the clock and the chiming mechanisms in 19xx. Now, the only reason for climbing the precarious ladder into the tower is to adjust the clock timing every couple of weeks. Currently the clock is accurate to about one minute a week, unless the temperature changes significantly, in cold weather it tends to run fast, and hot weather runs a little slower.

Picture of The All Saints Milton Birdcage Clock. Far left, electric motor for clock weights. Centre, gears driving the clock. Left, gears driving the bell chime mechanism. The electric motor for the bell chime is out of picture on the right.

 How the Clock Works

Having taken numerous pictures of the clock, I began to work out how our Milton Clock worked at home, with the help of pictures and drawings. The basic principle is that the clock has a pendulum which rocks an escapement. The escapement regulates how much the first clock gear can move. The gear then transmits its movement to other gears, slowing the rotation down, until the final one, which is linked to a minute arm on the outside of the clock. The minute arm goes once around the clock face in 1 hour. The minute hand is linked to the hour hand by another gear which drives the hour hand around the clock face. The clock is driven by weights and wound up several times an hour by an electrical motor.

The basic elements of the clock

The following photo and the diagram show all the timekeeping parts of the clock.

The pendulum (1)

Invisible from the from the front of the clock, an approximately 1.5 m long (4 ½ ft) pendulum swings from side to side from the top-most rod, T. This is the clocks heartbeat and is the accurate timekeeper. Each swing back and forth on the Milton clock takes exactly 2.5 seconds. It was Leonardo da Vinci who, sitting bored in a church, noticed the regular swing of a pendulum. He experimented further and found that the time a pendulum takes to swing is dependent on how long it is.

The anchor escapement (2)

The pendulum is linked via the rod T to a claw like element, the escapement. This rocks back and forth over the spikily toothed gear (3), and for every swing to one side and back again, it moves the gear on by one tooth. This is the action that creates the ‘Tick-Tock’. Tick when it rocks to one side and tock when it rocks back to the other. Each tick-tock takes 2.5 seconds. I’ve recorded the sound of the All Saints clock and you can listen to it here at https://archive.org/details/AllSaintsClockTickTock.

The All Saints clock is accurate to about 2 minutes every fortnight.

The gear train from (3) to the minute hand (9)

The Tick-Tock of escapement against teeth of gear 3 moves the gear on by one tooth every 2.5 seconds. Gear 3 has 30 teeth and so it does one full revolution every 75 seconds. The aim of the following gears is to slow down the final gear 9 with the minute hand so that it turns once every 3600 seconds, or 1 hour.

The stages are as follows:

The use of weights and electricity to power the clock

If the sole power on the clock was provided by the pendulum, then the clock would soon stop due to friction. The clock actually needs to have a power source that nudges the pendulum just enough to keep it swinging.

In the past, All Saints clock had weights (A) attached to a cable around a drum (B) on the same rod as gear 7 as shown in the figure below. Gravity pulling on the weights provided a steady source of power to the clock.

As the weight gradually turned the drum, it would sink lower and lower on the unwinding cable. When the weight was getting close to the ground, a church- or clock-warden would have to climb up to the clock and wind the weight back up again. This could be done without turning the clock backwards in time.

In order to avoid excessive climbing up and down ladders – and the associated risks and time wasted, the power system for the All Saints Clock was changed to an automatic electric winding mechanism.

The chiming mechanism

In brief, the chiming mechanism is driven by a separate set of weights and gears.

Currently, I have insufficient information and photos to show the mechanism in full.

Click here for footage of the mechanism chiming twelve (youtube link) from inside the tower. The chime was manually triggered after the clock stopped and needed to have the chime re-synchronised with the clock face. Unfortunately from up the tower you can't see what hour the face says, or what hour the mechanism thinks its on, so if they get out of sync (happens occasionally if the auto-winder fails, as the chime runs off a different weight to the clock itself, so the two halves can 'run out' at different times.) you have to manually advance the chime mechanism round until they are back in sync.

You can also listen to the noon chime of the bells here at https://archive.org/details/AllSaintsClockChimes.

Why do we have 12 hour, 60 minute, 60 second clocks?

In brief, we owe the 24 hour day divided into 12 hours at night to as far back as the ancient Egyptians. The first known mathematicians, the Sumerians, used a system based on the number 60. This was passed down to us through the Babylonians – to the Egyptians –Greeks – Romans – Arabs – Western civilisation. The idea of dividing an hour into 60 minutes and minutes into 60 seconds was already present in the 14^th century in Europe but clocks were not accurate enough to include minutes till the 17^th Century. The first known clock marking seconds was made at the end of the 16^th century, however, it wasn’t till the invention of the pendulum clock in 1656 that seconds could be measured accurately.

The division of night and day

To the earliest civilisations, Day and Night were two totally different entities. The rising and setting constellations from dusk till dawn were full of meaning and possible portents, both good and bad. From ancient Egypt to the early Chinese, the celestial clock was keenly measured with early astrolabes, and mathematics evolved to help calculate the seasons. Surely, if the stars, moon and planets could do that, they must have an influence on mortal beings, from kings to the most lowly slave – and astrology was born. The preference for calculations based on the number 12 led to the first division of the night into 12 hours.

For ancient Egyptians, a giant scarab beetle trundled the sun across the sky during the day and the first sundials, in the form of stele, measured its progress by the wandering shadow. The day too was divided into 12 hours. Both sun times and star times were important to call people to pray and sacrifice at the temples at the right times.

When does a 24 hour day start?

The idea of a 24 hour cycle of day and night became established. But when did a day start? Some began counting hours from sunrise to sunrise. The ancient Jews counted the hours from sunset to sunset. The Roman occupiers of Israel began their day at midnight. This has caused some confusion with scholars for quotes in the Bible giving an hour of the day – was the person using Roman time or Jewish time – there is a whole 9 hours difference!

Even today, the clocks start at midnight, but the Jewish day starts at sunset.

How long is an hour?

Even the ancient civilisations closer to the equator were aware that the 12 hours during the day and 12 hours during the night were unequal in length. Here, further north in Europe, the difference is really pronounced. At the winter solstice in Milton, we only have about 7 hours and 20 minutes of daylight. If the day were divided into the classical 12 hours, each ‘hour’ would only be 37 minutes long! At the summer solstice, our days are 9 hours longer – giving as day light of 16 hours and 24 minutes. This would make a classical one twelfth daylight hour last 82 minutes.

Early church sundials therefore sometimes had complicated additional lines, so that you could work out what hour of the day it was at any time in the season. No wonder people relied more on the chiming of the church bells to mark the passing hours of the day.

It took the invention of the ‘escapement’, a device for making a mechanical element stop and start at regular time intervals (the ticks and tocks of a clock), for mechanical tower and church clocks to be possible.

The first recorded escapement was invented in distant China by the military engineer Lian Lingzan and the monk and mathematician Yi Xing in 720 AD. He used it to make a water clock that could move planets and figures to show astronomical events. The idea finally reached Europe in the 13^th Century via Arab scholars. By the 14 century, simple escapements were used to ring bells called ‘Alarums’ (guess where the word ‘Alarm’ in alarm clocks came from). Gradually the first escapements were used in mechanical tower or turret clocks.

With the advent of mechanical clocks, the clock face was initially marked in 24 hours. The mechanical nature meant that the day and night were divided into 24 equal hours. It just became more convenient to refer to the mechanical clock time as the clock mechanism could be linked to strike bells at regular intervals.

Minutes and Seconds

The ancient Sumerians already had a mathematical system based on the number 60, more than 3500 BC. 60 was a useful number for early mathematicians because it can be divided by 12, 10, 6, 5, 4, 3 and 2. The system was passed to the Babylonians who had already thought of dividing an hour into 60 minutes, and each minute into 60 seconds in the 1800s BC, well before we had mechanical clocks. The system was passed down to us via the Greeks, Roman and Arab scholars.

Unfortunately, the first escapements in mechanical clocks were inaccurate – the best they could achieve was to within a quarter of an hour a day. As a result, early clocks only had hour hands. What they needed was a reliable system that could accurately keep time and pass this on to the clock mechanism.

It was a bored Galileo Galilei who came upon the solution – during a church service in the 1580’s. He noticed that the chandeliers in the church were swinging. Using his pulse as a time keeper, he discovered that a pendulum (like the chandelier) swings backwards and forwards at regular time intervals. The length of time for a swing is determined not by amount of swing, but by how long the pendulum was. In fact, a pendulum 99.3cm long will swing from one side to another in 1 second.

It took until 1656 for the Dutch scientist Christiaan Huygens to build the first pendulum clock. In 1657, Robert Hooke in England followed with the invention of his Anchor escapement, linked to a pendulum. Suddenly, clocks were accurate to a minute a day. Our church clock has a minute hand thanks to Robert Hooke’s invention and is accurate to about a minute a week.

The second hand did make an appearance on early German clocks in the 1580’s, but truly accurate second hands only reappeared in the 18^th century, mainly on pocket watches and scientific time-keepers.

Whilst the All Saints clock does not have a second hand, listen to its Tick-Tock. Each Tick and each Tock occurs at about 1.25 second intervals. There are 24 ticks and 24 tocks (combined 48 Tick + Tocks) in a minute. You can hear it here at https://archive.org/details/AllSaintsClockTickTock.