Verge escapement

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This article is about the clock escapement mechanism. For the role playing game engine, see Verge (gaming).

The verge escapement is the earliest known type of escapement, the mechanism in a clock that maintains the swinging of a pendulum. Its origin is unknown, but appears to date to about 1275. Verge escapements were used for almost all clocks until the anchor escapement was introduced around 1671. In England the anchor escapement took over, but in France the verge was used for the next 100 years.

Many original Bracket clocks have their Victorian made anchor escapements conversions undone and the original style of verge escapement replaced. Clockmakers call this a verge reconversion. These clocks keep quite reasonable time when properly made and this is why the French continued to use them until about 1800.

The verge escape wheel has teeth protruding from the side of the wheel. The pallet arbor is in front of the wheel and has 2 flags or pallets, which enter the spaces between the wheel teeth in such a way as there is only ever one pallet at a time between the teeth. One pallet acts on one side of the wheel, say the 12 o'clock position, and the other at the 6 o'clock position. The pallet arbor rocks back and forth due to the pendulum's motion, and as each tooth moves in and out of the teeth, allows the wheel to turn tooth by tooth.

Before the introduction of the pendulum, verge clocks were not very accurate, but the application of the pendulum suddenly brought the timekeeping from a variable accuracy of plus or minus an hour a day to within minutes a day. So the verge escapement is not inherently inaccurate, as the result of the introduction of the pendulum proves. Furthermore the first successful chronometer made by John Harrison used a verge escapement. This can be seen in the pieces he made which are in the National Maritime Museum, Greenwich, and H5 which is in the Clockmakers' Museum London. Whereas the verge escapement may have problems, it is capable of good timekeeping.

There are three problems with the verge mechanism:

It is an escapement of the frictional rest category.
It is a recoil escapement.
Recoil and friction interfere with the free swinging of the pendulum, as is the case in the anchor escapement.

The clock can be made to lose or gain by varying the power to the escapement. A big advantage was that with such a large pendulum amplitude, a clock did not have to be carried so delicately around the house.

[edit] References

Bolter, David J., Turing's Man: Western Culture in the Computer Age, The University of North Carolina Press, Chapel Hill, N.C. (1984). ISBN 0-8078-4108-0 pbk. Very good, readable summary of the role of "the clock" in its setting the direction of philosophic movement for the "Western World". Cf picture on p. 25 e showing the verge and foliot. Bolton derived the picture from page 20 of: