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History of Wooden Gears and the Pendulum Clock

Introduction

This brief overview offers only a glimpse of developments involving wooden gears and pendulum clocks. On any topic, consult the references listed on the final page, for a more complete treatment.

Verge and Foliot

In a verge and foliot clock, two weights on a pivotted beam, suspended on a thread, are simply pushed to-and-fro against a slowly rotating crown wheel, powered by a drive weight [1]. The earliest verge and foliot clocks for indoor use were made in metal since the first by Henry de Vick, in 1360 [2], but later models were also made in wood. Wooden works clocks were made in Germany [3,4] beginning in the 17th century. Cuckoo clocks, including wooden versions, were also made there from 1750 onward.

Oscillation period is directly related to the verge and foliot clock's drive weight which powers the crown wheel. The foliot is not a resonant system, as it contains no spring. Thus all the energy required has to be repeatedly supplied, and taken back, through the verge, for every oscillation. The force transmitted by the verge is very high, so friction effects cause errors of at least 15 minutes per day. Indeed, if you would wish to improve the accuracy of a verge and foliot clock by reducing the friction and drive weight, install a spring to make the foliot into a resonant system. We will see later that the verge is capable of much better, if used with much lower force, to switch a resonant system.

Pendulum in Italy and Holland

The pendulum introduced by an Italian, Galileo Galilei (a weight on a chain) was used by physicians to measure heart rates, and by physicists including Galileo, to measure dynamic events. Astronomers needing to measure transit times of planets and moons, would simply count the oscillations during the transit. When necessary, the pendulum oscillation was regenerated by synchronized impulses applied by the hand of the observer or assistant. It was apparent to many astronomers, including Galileo, that a machine could effect these two operations of counting and regeneration. But the actual construction was quite difficult for the time, and several attempts proved unsuccessful. Galileo had a design with a model which wasn't completed; only a long-lost drawing of it was discovered many years later. When Johannes Hevelius asked a craftsman to build one, he refused, on the basis that it was too ridiculous [3]. It was Christiaan Huygens who first combined a pendulum with a verge clock, in 1656. In 1657 he had a pendulum clock made by Salomon Coster and patented in the United Provinces (the Netherlands), and it was published in Horologium in 1658 [5]. The improvement was so dramatic that other clockmakers followed suit. Many existing verge and foliot clocks were modified similarly, by discarding the foliot and installing a pendulum. Huygens' detailed pendulum theory regarding circular error, however, clearly showed that the verge was unsuitable [1], and a new escapement was needed.

Pendulum Clocks in England

Huygens permitted Salomon Coster to provide training on pendulum clocks to John Fromanteel, son of a London clockmaker. After he brought the new skills back to London in 1658, the Fromanteel family made the first longcase clocks, using a verge and a short pendulum [3,4]. In 1666, Robert Hooke introduced the frictionless, flexure suspension for pendulums [4]. The recoil-anchor escapement introduced by William Clement and Joseph Knibb in 1670, allowed long pendulums swinging through a short arc, so that very precise longcase clocks could be made [6]. Thomas Tompion, Richard Towneley, and George Graham developed the dead-beat anchor escapement by 1715, which is used in many longcase and regulator clocks to this day [6]. Graham also introduced the first temperature-compensated pendulum, by using a special mercury container for the bob.

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