# Pendulum clock

Louis XV pendulum clock, by Mathäus Funk (around 1745)
German pendulum clock of the 19th century, brand Gustav Eduard Becker
Sumiswalder Pendule ( Stockuhr ), approx. 1850–1870
Pendulum clock in the Villa Hammerschmidt

The pendulum clock , even Pendule or Pendüle called, is a clock whose clock a mechanical pendulum (obsolete also: pendulum ) is. The oscillation of the pendulum determines the timing, an approx. 1 m long pendulum (exactly 0.994 m) swings from one side to the other in 1 second. The shorter the pendulum, the more often it swings per second.

Pendulum clocks come in various forms, especially as a tower clock , wall clock , table clock or floor clock . Because of the interference with the pendulum movement caused by external accelerations, they are fundamentally unsuitable for moving clocks, such as wristwatches or clocks on vehicles.

In 1632, Galileo Galilei formulated the pendulum law , which in its original form says that the period of oscillation of a pendulum is independent of its weight and only depends on the pendulum length. With this, Galileo meant that the period of oscillation does not depend on the oscillation amplitude ( isochronism ), but this only applies in the limiting case of small oscillations. These properties of a pendulum form the basis for the construction of pendulum clocks. Galileo's son Vincenzio tried (unsuccessfully) to build a pendulum clock.

It was also around this time that Christiaan Huygens (including the inventor of the balance wheel with a spiral) was concerned with the theory and design of the pendulum clock. The first (functional) pendulum clock with verge escapement designed by Huygens , which is now kept in the Rijksmuseum in Leiden, was built by the master Salomon Coster in 1657. It had a rate deviation of about ± 10 s per day. This value could only be improved to less than a second per day 100 years later when John Harrison beat his Time Keeper No. 4 , but instead of a pendulum it has a balance wheel.

## description

The principle of the pendulum clock is based on the fact that a swinging or rotating pendulum triggers an action in the clockwork at a certain point of its path with each passage, whereby the time display is switched further (this is most often done by the helical gear and lever escapement). In addition, the pendulum receives an impulse ( lifting ) from the clockwork or another drive so that the oscillation is maintained despite the loss of energy through friction.

The regularity of the pendulum movement is decisive for the accuracy of the clock, which is why great attention is paid to the construction of the pendulum and the triggering of the action in the clockwork. The friction of the pendulum suspension was soon reduced by agate bearings, the swaying was reduced by pendulum springs , the even power transmission to the pendulum via a pendulum rod was improved and the air resistance was reduced by sleek pendulum lenses. Changing external influences on the period of oscillation such as temperature, air density and humidity can be compensated for. A low-friction release of the movement and an even transmission of impulses from the movement to the pendulum are further prerequisites for good rate results.

The adjustment of the oscillation period of pendulum clocks is done by changing the effective pendulum length.

## Short Story

• In 1637, Galileo Galilei saw the possibility of measuring time with a pendulum clock without building a corresponding clock. His son constructed a preform of the pendulum clock, but did not use it to measure the time, but used the device to measure vibrations.
• In 1657, Christiaan Huygens patented an escapement that improved accuracy to ten seconds per day.
• In the 1680s, hook and anchor escapements are invented and the pendulum suspension on the thread is replaced by a thin steel spring ( pendulum spring ). Formulas for the influence of the amplitude become known.
• In the 1720s, George Graham (inventor of the escapement of the same name ) and John Harrison developed the temperature-compensated pendulum independently of one another, which improved the accuracy to about one second a day.
• In 1843 the electromagnetically driven pendulum was patented - an approximately tenfold improvement and the first step towards the electric clock.
• Around 1870, precision pendulum clocks achieve a daily accuracy of less than a tenth of a second and are used as a time standard for astronomical time services.
• 1921 Development of the Shortt clock (daily error less than 0.01 s)
• 1923 Patented battery-operated pendulum clocks by Marius Lavet and Léon Hatot
• From 1933, temperature-stabilized high-precision quartz clocks replaced the precision pendulum clocks.

## Vibration accuracy

The oscillations of hanging, stable pendulums, which rotate around a horizontal axis , are more uniform than other pendulum oscillations. Such inaccurate processes are, for example, the vertically oscillating spring pendulum (see harmonic oscillation ) or a simple thread pendulum . Both can hardly exceed an accuracy of 0.01 percent, whereas a shielded compensation pendulum, for example , can achieve 0.0001 percent (10 −6 or ± 0.1 seconds per day). Special constructions come in the range of a few ms per day.

In classic pendulum clocks, the oscillation is converted into a step-by-step rotation of the escape wheel via the escapement , which in turn is driven via a gear train, for example by the clock weight , in order to be able to deliver a metered impulse to the pendulum.

The pendulum of electric pendulum clocks gets its energy from a coil, which is supplied with electrical current at the right moment via pendulum contacts or another control. The coil moves the pendulum made from a permanent magnet . The coil itself can also be used to obtain the control signal by utilizing its mutual induction voltage . The lower damping in such clocks and the more easily achievable constant amplitude of the pendulum improves the accuracy considerably.

One of the most accurate pendulum clocks is the Shortt clock, which has been largely free of interference . In the master clock, an almost free pendulum swings in a vacuum . A second clock, synchronized with the master clock, contains all other moving parts that would affect the master clock. The error of this clock is a few milliseconds per day. This accuracy was only surpassed by temperature-stabilized quartz watches around 1933 .

## Special forms

### Astronomical pendulum clocks

Astronomical pendulum clocks are clocks with particularly high accuracy, which usually have a second pendulum.

The second shock allows for measurements of star passageways - as in the telescope of a meridian circle - the exact correlation of time with the through field . Withdrawing Star (up to 15 "/ s) with the so-called eye-ear method can time measurements up 0.1 To be carried out precisely to a second .

The rate regulation (calibration) of pendulum clocks takes place by means of adjusting screws at the lower end of the pendulum or by means of weight plates.

The temperature compensation of good pendulum clocks takes place by means of three-bar pendulums or mercury pendulums . The center of mass or the rod length of the pendulum are influenced in order to compensate for the thermal expansion of the pendulum and the resulting temperature dependence of the oscillation frequency. The dependence of the period of oscillation on the air pressure can be reduced with the help of the aneroid can compensation or compensated by encapsulating the pendulum.

### Reversion pendulum for gravimetry

A pendulum that can be turned around and has the same period of oscillation around both axes (usually agate edges ) is called a reversion pendulum . This technique allows the exact measurement of the pendulum length and therefore also the acceleration due to gravity using the pendulum formula above . ${\ displaystyle g}$

The earth's gravitational field was explored in a similar way as early as the 18th century . The shape of the earth was determined and the meter was defined through a combination of gravimetry and geometric degree measurement .

Today, high-precision spring balances , the so-called gravimeters, are used for this .

## Private pendulum clocks

Floor clock
Rotary pendulum clock

Private pendulum clocks usually have pendulum lengths of 15 to 25 cm; The latter corresponds to about 1 [s] oscillation period. They achieve an accuracy of a few seconds per day. Shorter pendulums swinging in front of the dial have so-called zapplers, two swinging pendulums are called double zappers. They are table or short wall clocks whose case is only closed on the front side. Its accuracy is ten seconds a day.

### Floor clocks

Floor grandfather clocks, also called grandfather clocks or house clocks for short, have a weight drive and longer pendulums with a small amplitude and thus good prerequisites for higher accuracy.

### Rotary pendulum clock

Rotary pendulum clocks use a torsion pendulum as a time base instead of a pendulum swinging back and forth . Torsion pendulums have very little damping because they move slowly and therefore the air friction is low. Rotary pendulum clocks can therefore run for a very long time with an elevator (e.g. one year). Rotary pendulum clocks can - just like ordinary pendulum clocks - also form their own pendulum (i.e. rotate or oscillate as a pendulum mass). In the case of rotary pendulum clocks, however, this leads to inaccuracies in the rate due to the expanding spring. Rotary pendulum clocks require so little power that they can only be driven by the air pressure and temperature fluctuations in their environment ( atmospheric clock ). Such watches have a winding mechanism that works with a pressure cell similar to that in manometers.

### The end of the pendulum clocks

In 1933, Scheibe and Adelsberger from Berlin designed the first quartz clock and thus heralded the end of pendulum clocks. Nowadays, a quartz watch easily rivals a precision pendulum watch in terms of accuracy.

The ornamental clocks with swivel pendulum (often with imitation brass balls ) or small, fast pendulums, which are mass-marketed nowadays, are actually quartz clocks - they have an additional electric drive for the movement of the pendulum just for decoration.

### Eyecatcher

An eyecatcher is a clock in which the eyes of a figure move with the pendulum.

### Mystery use

This is a swinging pendulum clock in which the pendulum and clockwork form a unit.

### Miniature zappler

The miniature zappler is a showcase object that was very popular in the 19th century. The small size made it difficult to read the time. The accuracy was very low and the miniature zappler had to be wound up every day due to the small spring.