Dorrin K Mace, Horologost

Dorrin K Mace, Horologost
The Clock Man in a pensive moment

Tuesday, October 18, 2011

Salisbury Cathedral Clock (Oldest working clock in the world)

A clock in Salisbury Cathedral that struck the hours was mentioned in 1306. This was probably one of the precursors of the 1386 clock, one of the many early examples of mechanical water clocks that are mentioned from c. 1280 onwards.
The clock was found in the cathedral in 1928. It had a pendulum, which appeared to have been installed at a later date. The clock was restored in 1956, and a verge escapement and faliot were installed. There were no drawings or documents available, so it is unlikely that the original foliot and verge escapement looked exactly like the one now installed in the clock.
The striking train of the clock is believed to be original.
Like many of these more practical devices, its main purpose was to strike a bell at precise times. It probably did not have a dial. The wheels and gears are mounted in a four-post wrought iron frame. The framework was not held together with nuts and bolts (which had not been invented), but rather with metal wedged tenons.
The escapement was a verge escapement with a faliot, standard for clocks of this age. The power was supplied by two large stone weights. As the weights descend, ropes unwind from the wooden barrels. One barrel drives the going train which is regulated by the escapement, the other drives the striking train whose speed is regulated by the fly (air brake).
Before the weights reach the floor, they have to be wound back up again, a task that explains the presence of two large wheels shaped like steering wheels at either end of the clock.
The clock was a 'single strike' clock that struck only on the hour. It made one strike per hour of the day (e.g. 12 strikes at noon). The left half of the clock is the striking train; the right half is the going train.
At the end of the 17th century, the Salisbury clock, like many others, was modified from verge and foliot to pendulum and anchor operation. This usually made clocks much more accurate, even though trials in the early 1990s by Michael Maltin showed that the clock was running to within two minutes a day if the rope on the barrel was kept in a single layer. As soon as there are two layers, there is more force applied to the barrel by the weight and the clock will go faster. As a single layer of winding is enough to keep the clock going for 12 hours, it could have been kept exact to within 2 minutes per day if it had been wound twice per day.
In 1790, the old bell tower 'on the ditch of the close of the canons of the said church' mentioned in the deed of 1386 which had housed the clock was demolished, so the clock was moved to the Cathedral's central tower. In 1884, a new clock was installed and the old one was left to the side.

The clock was re-discovered in the tower in 1928 by T.R. Robinson, an horological enthusiast who went up the clock tower to see the new clock (installed in 1884). The presence of the old clock was known to many, but nobody attributed much importance to the old clock. It was only T.R. Robinson who believed that it was the clock mentioned in 1386. From photos taken in 1928, it looked to be fairly complete. Eventually its historic importance was realized. It was first put on display in the Cathedral's North transept. Then, in 1956, the clock was restored to its original condition and started working again. The pendulum and recoil escapement were replaced by a new verge and foliot escapement, thus restoring the clock to something like its original design.
Today, the escapement operates, but the striking mechanism has been disabled.

John Smith & Sons, of Derby, received the clock in February 1956. It was taken apart for the transport. They reassembled the clock in their workshop and compared it to existing clocks in the Science Museum before deciding how to restore it. The help of Rolls Royce was enlisted to have X-ray photographs of two of the wheel arbors taken. This confirmed that the two arbors of the going train had been lengthened when the clock had been converted to pendulum operation. Subsequent investigations revealed that the clock had actually been converted twice, as remains of an earlier pendulum escapement were discovered.  The 1956 restoration included the following:
Train Part Previous work 1956 Restoration
going train great wheel disc with two pins attached to great wheel as it only turned once every two hours due to conversion to pendulum after removing the disc, the original hole for the pin was discovered and a new pin was fitted 
going train escape wheel replaced with anchor escape wheel new escape wheel forged, teeth marked out by hand, riveted onto existing second wheel
going train winding barrel
new wooden winding barrel fitted
going train foliot support bracket
new foliot support bracket forged and fitted
going train foliot
new foliot forged and fitted
striking train hoop wheel flange of hoop wheel reversed flange of hoop wheel replaced correctly
going train turning direction, strike release strike release moved to front of frame, rotation of going train reversed to clock-wise to fit clock dial (1613) strike release moved to back of frame, rotation of going train reversed to counter clock-wise as it was originally 

For a clock that was nearly 600 years old at the time, these repairs/restorations are minimal.

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