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World's oldest (original) clock?

The clock found in Dover Castle, Kent may be a couple of centuries off being a contender for title of the World's oldest clock but it calls for inclusion in this series because it has the oldest (original) foliot balance, a 14C form of escapement to regulate time-keeping.

In a sense, the design of this turret clock movement, which dates from c.1600, was "après-garde" (to coin a new phrase) because it was way behind its time. The foliot balance was just about to be replaced by foliot/pendulum and pendulum/recoil escapements, which were found to be much more accurate. Indeed, it was because of its foliot balance that the Dover Castle clock was once believed to date from the 14C. It was only when the 14C Salisbury clock was rediscovered in 1929 that it became obvious that the structural construction methods of the Dover clock were much later.

So what sets the Dover clock apart is that unlike every other old medieval turret clock, the foliot balance was never replaced with a pendulum. The reason it wasn't converted to pendulum are unclear but there is nothing to show that it was ever installed at the Castle so probably there was no reason to update it.

The clock's history is vague. There are suggestions that it was salvaged from a nearby church or from a French chateau and left on the quay side by an army officer returning from Waterloo who left England again immediately. There is no evidence to support these theories, nor the Castle Armourer's claims that the date 1348 was once carved into a plate that was stolen from it. But the claims can be discounted because the clock's ornamentation post-dates 1450. However, it does bear a strong resemblance to a clock in Quickswood Farm in Hertfordshire, which can be dated to 1625.

The only real certainty being that it was first discovered in the Castle in 1851 when it was removed and taken to the Science Museum in London and it remains the only known turret clock of its time still to have its original foliot balance working. Indeed, in 1956 it was studied and copied for the restoration of the Salisbury Cathedral clock back to its original foliot balance design.

Most readers will already recognise a recoil escapement and know what a pendulum looks like. The bottom two illustrations help explain the foliot design. The first one is animated and shows the crown wheel, powered by weights, pushing the top and bottom pallets on the verge out of the way, one after the other. Along the horizontal bar fixed to the top of the verge are two weights, the position of which can be adjusted to regulate the time taken to swing back and forth, thus controlling the time-keeping. See how this principle is applied to the Dover clock movement in the two photographs above.

The final illustration shows how the foliot design was developed to accommodate the more advanced and much more accurate pendulum. The crown wheel (C) has moved to a horizontal position and the verge (V) containing the two pallets (P) is now able to support a pendulum at one end. The length of that pendulum (and to some lesser extent the weight of the bob at the bottom of it) now controls the duration of each swing (or oscillation).

Finally, you must forgive the erroneous mathematical design of the crown wheel in this final illustration; there is a very good reason why unlike the animated illustration above, this one remains static. The fact is it wouldn't work! The crown wheel must always have an odd number of teeth; the artist has given this one twelve and so it could not possibly keep turning as the pendulum will not receive half of the impulses it requires to keep swinging.

Click here to read more about the next clock in this series of articles, the electric ROYAL OBSERVATORY clock.


DOVER, ENGLAND

  • Dover Castle
  • Dover Castle clock movement
  • Dover Castle's clock movement from the side
  • A working illustration of a clock foliot and crown wheel
  • How the foliot was adapted to take a pendulum