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Introduction

This brief overview offers only a glimpse of developments involving wooden gears and pendulum clocks. On any topic, consult the references listed below, 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.

Longitude

An important unsolved scientific problem in the 17th century was the measurement of longitude on ocean voyages [7]. Unlikely as it may sound, the wooden-gear clock played a critical role in its solution. Longitude prizes were offered by governments of Spain, Italy, France, the Netherlands, and Britain. Galileo proposed using his newly discovered moons of Jupiter to provide the absolute time, and therefore longitude, by monitoring their eclipse, by telescope. His method was used extensively for longitude on land, but proved difficult on a moving ship. Most scientists, including Isaac Newton, believed that Galileo’s method, combined with similar observations of our moon, assisted by a book of lunar tables, would offer the best solution. German astronomer Johannes Werner had proposed this lunar method in 1514 [7].

In 1530, a Dutch astronomer, Gemma Frisius, showed that portable, mechanical timepieces would provide the longitude, if they could be made to operate with sufficient accuracy [7]. Huygens made gimbal-mounted, marine pendulum clocks which provided acceptable absolute time and longitude on trial voyages in sufficiently calm weather, but their accuracy was far worse in stormy weather. Although he published the method in 1665, he went on to develop the spiral-spring balance, patented in 1675, for marine timepieces, and other clocks and watches. Huygens’ spiral-spring balance was a rotational spring-mass oscillator, different, yet in the general class of those proposed by Robert Hooke in lectures from 1664 [4]. Between 1675 and 1680, as a charter member of the Royal Academy of Sciences in Paris, Huygens had his first longitude timepiece made by Isaac Thuret, the Royal Academy clockmaker [8]. Further refinements followed in Paris, and by 1766, Pierre Le Roy had developed a longitude timepiece with the three essential components of modern marine chronometers: 1) detached (detente) escapement, 2) isochronous spring and 3) balance wheel with internal temperature compensation [3,7]. With it, he won the first longitude prize, the Paris Academy of Sciences double prize in 1769.

John Harrison

Meanwhile, the members of the British Board of Longitude believed that nature’s clockwork would provide the best measure of longitude, rather than a mere mechanical representation, like a clock. They regarded it as an unwelcome surprise that their prize would be won in 1773 by a country carpenter, John Harrison, using unconventional methods [7]. Their opposition was so strong and persistent, that Harrison was only granted the final installment with the intervention of King George III. His final timepiece, H4, completed for him by John Jefferys in 1759, contained none of Le Roy’s three modern components. Rather, he used his own temperature compensation, fusee, maintaining power, remontoire to regulate the power train, and a modified verge [4] with Huygens’ spiral-spring balance wheel, in a diamond-jeweled, 5 inch diameter timepiece. This, and Le Roy’s timepiece were the ones predicted by Hooke and Huygens, a century earlier, and by Frisius two centuries earlier.

John Harrison was a self-taught expert horologist, who had honed his skills on wooden-gear clocks. By 1715, he had built two wooden-gear longcase clocks, containing conventional escapements [6,7]. By 1722, with his brother James, he had built a wood-works turret clock at Brocklesby Park, an estate near Barrow upon Humber; this clock still runs today. By 1728, he had built several wooden-gear regulator clocks with his own frictionless, grasshopper escapement [4,6,7,9], and lantern pinions with lignum vitae rollers [6,7]. Harrison needed two in separate rooms, to test his new invention, the gridiron pendulum, at different temperatures. Although the quiet grasshopper escapements were difficult to hear, by removing the covers from the two regulators, he was able to listen to both together. Only after these tests, was he able to proceed to build his four marine clocks, all of which required temperature compensation. H1 contained wooden gears, and proved successful on its only voyage to Lisbon and back. H2 and H3 were improved brass models, which were never tested at sea. His best wooden-gear regulator was adjusted to an accuracy of 1 second per month, measured according to a star as it passed his neighbor’s chimney [6,7]. He then adjusted the marine clock to match, prior to delivery to a ship’s captain for ocean trials. Harrison’s winning entry, H4, was extremely important and valuable, in that it encouraged and accelerated chronometer development in France and England. But H4 was so expensive and complicated that, except for his maintaining power system, most of its design features would not become part of the modern marine chronometer. By 1785, John Arnold and Thomas Earnshaw had developed the modern form of marine chronometer, using the methods pioneered by Le Roy.

If a marine chronometer ever stopped, it needed to be restarted and reset by the lunar method; nature’s clockwork never stops. In addition to this difficulty, the considerable expense of available chronometers meant that the astronomers’ method was preferred by many captains. This method involved sextant and prepared lunar tables, and remained the most commonly used method for many years to follow. A good example is the Lewis and Clark expedition to survey across North America to the Pacific; mainly the lunar method was used, with a marine chronometer playing a supplementary role [10]. By the early 20th century, time signals via radio telegraphy, then WWV on short-wave radio, and later the GPS system had rendered the lunar and chronometer methods obsolete, although they may still be used as back-up systems.

America’s Wood Clocks Industry

By 1800, many wood works tall clocks had been made in the New England states. For some years, Britain’s trade embargo prevented brass and fine steels from reaching the new country. The Boston Tea Party had already shown what Americans thought about buying British goods with high taxes, including metal clocks. The market demand was high, so clockmakers learned to make wooden clocks, instead. Only a few parts were made of steel or brass, such as the escape wheel and anchor escapement. This was the high-tech industry of the day, and their products represented pride in independence from Britain, and patriotism for their new country. Clocks which included pictures of George Washington, his Mount Vernon residence, American flags, and other patriotic scenes were received well by those who needed clocks, and are still highly regarded today. Tall clocks evolved into unique American styles, using new manufacturing methods. Adapting Eli Whitney’s factory methods, Eli Terry set up a clock factory to use truly interchangeable parts, which transformed the industry [1]. Smaller clocks like the wag-on-the-wall, Simon Willard’s banjo clock, and the lyre clock were also developed [4]. Terry developed a wooden-gear shelf clock [3], which would be made by many local manufacturers, including Seth Thomas [11], in 30 hour and even 8-day models [12]. The tall case clock was no longer produced after 1825 [3]. In 1837, the availability of metals like rolled brass allowed Chauncey Jerome to start manufacturing metal works clocks [1]. Others followed suit, bringing the wooden clocks era to a close. But the American factory methods pioneered by Whitney and Terry were a model for other industries. By 1913, Henry Ford, a clock repairer in his youth, introduced mass-production techniques for manufacture of inexpensive automobiles.

Torsion Pendulum

A torsion pendulum with a very long oscillation period may be made using a balance arm with two or more weights, freely suspended by a long wire, like the foliot in the old clocks [1,2]. Charles Coulomb, in France in 1785 used a torsion balance to measure electric charge for the first time. His name is now used for the unit of charge measurement. In England in 1798, Henry Cavendish used one with a 7 minute period to measure the gravitational attraction between metal spheres within his laboratory apparatus [13,14]. His quartz-fiber torsion pendulum carried two of the spheres, while allowing frictionless movement, with the earth’s attraction neutralized.

Between 1840 and 1860 in New Jersey, Aaron Crane invented the torsion pendulum clock, in versions running 8-days, a month, and finally, 375-days [15]. These were about the size of the earlier shelf clocks. Unlike the verge which was connected directly onto the foliot, Crane connected his escapement onto the torsion ribbon, near the support point, at the top end. He used his "walking" escapement, which is similar to Harrison’s grasshopper escapement, except that cams are needed to guide the pawls into the escape wheel. Therefore, it would certainly be possible to make a wooden-gear torsion pendulum clock.

The modern clocks derived from Crane’s year clocks are usually much smaller, mounted under a glass dome, and are named 400-day, or anniversary clocks. These generally contain dead-beat escapements. The Atmos clock developed by the firm of Le Coultre in Switzerland is a very special torsion-pendulum clock which needs no winding at all, yet keeps running by itself, with no intervention. Although this may sound like a perpetual motion machine, it is not. Rather, it is more like a highly miniaturized steam engine. Its liquid-vapor phase-transition chambers draw energy from subtle ambient temperature variations, winding the mainspring to keep itself charged [16].

Conical Pendulum

The first clock with a conical (rotating) pendulum as one of its options, was a turret clock by Jost Bodeker in 1587 [4]. Huygens experimented with isochronous conical pendulums constrained to follow a parabolic path. There was renewed interest in the 19th century, and clockmakers like E. Farcot in France produced some elaborate and elegant clocks with a conical pendulum in plain view. A small clock with a conical pendulum was designed by John Briggs in 1855.

Foucalt Pendulum

In 1851, Leon Foucalt stunned the world, as his long pendulum in the Pantheon in Paris provided the first dynamical proof of the earth’s rotation [17]. The Foucalt pendulum swings in a plane which resists rotation, while the earth rotates beneath it. He later invented the gyroscope, with which he then arranged an experiment to illustrate the same effect. It was recently demonstrated that a 70 cm long Foucalt pendulum "wall-clock" may be made to show the effect, and display the time [18].

Electric Pendulum Clocks

Many different forms of electrically-rewound, electromagnetically impulsed or electric-remontoire pendulum clocks have been developed [6,16]. These include the most accurate pendulum clocks ever made, the nearly-free-pendulum clocks and the Shortt-Synchronome free-pendulum clock [6,9,16]. Most tower (or turret) clocks are pendulum clocks, electrically rewound using Huygens’ endless chain system [11].

Quartz

Since 1970, quartz clocks and watches have become increasingly affordable and popular. The quartz clock has been in continuous development since the first one was developed by Warren Marrison, in 1927 [2], and is currently the most common timepiece in use. More recent are radio-controlled quartz clocks and watches which accurately reset themselves several times per day, to the best atomic clock time available.

Ornamental Pendulums

Some synchronous-motor clocks contain pendulums as kinetic ornamentation; these generally move in a contrived to-and-fro motion, guided by a cam follower. A quartz timepiece has no requirement for a pendulum as these two competing technologies are as different as night and day. Nevertheless, some quartz clocks do contain a moving pendulum in the package, which attests to the enduring popularity of pendulum clocks. Rather than being an annoyance, the moving pendulum lends aesthetic advantage. Many anniversary clocks contain ornamental pendulums, rotating separately from the quartz timepiece. While modern electronic timepieces have technically superseded the pendulum clock in terms of accuracy, it is extremely unlikely that they will ever eclipse the pendulum clock and the ambience it provides. Moreover, it seems inevitable that radio-controlled quartz clocks will soon sprout pendulums also.

Thermostat Control

Long ago, houses were heated using a fireplace, without precise controls. Harrison’s bi-metal coil is used today as a temperature-sensing switch, inside thermostats for controlling indoor temperature [7]. Ironically, Harrison’s invention, indirectly, has a positive effect on most timepieces, including those without his gridiron pendulum. Most clocks run much more accurately in a constant-temperature environment. Clocks with steel pendulum rods, and those with ornamental "gridiron" or "lyre" pendulums [16], will operate very accurately in such a temperature-controlled environment. Even turning the thermostat down by 10 degrees Fahrenheit for the night, will cause an error of less than 1 second per day, which is negligible for most purposes.