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The pendulum clock

The speed of the clock is the only thing that controls timekeeping. Adjusting the pendulum will make the clock go faster or slower. All other factors can be considered constant. This can be seen from the equation relating to the period of swing of a simple pendulum.

T = 2π√(L/g)

where

T is the period in seconds (s)

pi = 3.14 (it is also written as the Greek letter π)

L is the length pendulum in meters or feet

g is the acceleration due to gravity (9.8 m/s² or 32 ft/s²)

Lengthen pendulum to go slower and vice versa

If your antique clocks are correctly set up and are fast and gaining time, you will need to lengthen the pendulums. If your clock is slow, you will need to shorten the pendulum of the clock, to quicken it up.

All clock pendulum rods and bobs prior to the temperature compensated pendulums either will expand or contract with temperature changes. They need to be adjusted accordingly. Most antique clocks in centrally heated houses will be re-markedly accurate though, after you have adjusted to your mean temperature.

Temperature Compensated Pendulums on Clocks

Probably the earliest method for trying to overcome deviations in timekeeping as a result of temperature changes was the wood rod pendulum. In long grain the wood rod will expand only a little.This expansion will be compensated by the addition of a large brass cased lead bob. This brass bob will also expand slightly up and down from the rating nut, with temperature changes.

Every Increasing Accuracy

Refining the accuracy of the very best precision clocks started from the early 18th century with Harrison’s grid iron pendulum. Differing expansions of metals was understood many years earlier. Harrison devised a pendulum with a specific proportion of brass and iron. These two metals would have rates of expansion and contraction that would effectively cancel each other out.

George Graham

In 1722 Graham produced a mercury compensated pendulum. The mercury as seen in a regulator clock in the picture above is contained in a jar. This is effectively acting the same as a normal brass pendulum bob. Mercury will expand roughly 6 times the rate of steel and so in the ratio 1:6. The expansions will roughly cancel each other out. The thermal coefficients of the differing metals is therefore important when building compensated pendulums. Glass being a poor conductor of heat was the only real negative to this invention but this method proved very effective and the pendulums do look stunning. These type of clocks are very collectible.

John Ellicott

There were various other pendulum’s developed like Ellicott’s compensated pendulum and Richie’s compensated pendulum on regulator clocks.Then the eventual use of metals like Invar which is a mix of nickel/iron and small quantities of carbon and manganese.

Conculsion

All these compensated pendulums are just trying to keep the effective length of the pendulum the same. When I say effective length of the pendulum, this will be from the bending point of the feather at the top of the clocks pendulum, to the centre of gravity of the pendulum near its bottom. This is why on some clocks coins or small weights were added on the rod to change fine timekeeping. I will happily answer more question if you contact me.

Time is at the heart of life itself. From the moment we are born, to the moment we die, man has always been intrigued by time. From the earliest days on earth, even pre-historic man lived by a form of time. Life for them revolved around light and dark: sleep, wake, hunt, eat,sleep again. Life and time are cycles that we cannot stop, we cannot slow. What the early mathematicians and astronomers tried to do was make time more exacting.

‘Water clocks’, ‘candle clocks’, and early ‘sundial clocks’ were developed, many of these in countries like China. It is amazing the evolution of countries over time, China played a huge part in the introduction of many new ideas and inventions, in the early world. It was in the UK that developed the measurement of time and put it in a more practical way. All these early antique clocks show the passing of time and try and measure it. Sundial clocks like Cleopatra’s Needle dating from about 1500 BC, was brought to England in 1877 and now stands on the Thames Embankment in London. Forms like Cleopatra’s needle and later sundials all use the elevation of the sun in the sky to tell the time.

Equation of Time

As society developed a more accurate way of measuring time was needed. Sundials, all well and good, are a pretty useless way of telling the time on a cloudy day. Also sundials are not accurate, because of the eliptical rotation of the earth. This inaccuracy is up to 15 minutes per day, sometimes slower, sometimes faster than sundial time. Mathematicians developed a yearly equation of time sheet for these inaccuracies. From this, is was possible to set your clock from these sheets.

Some amazing clockmakers produced this equation of time feature, on a year calendar, on their actual clocks. Setting you clock in the 17th century was not easy though and many were still not accurate. It was not until the introduction of the long pendulum, invented by Christian Huygens in 1657 did both clocks accuracy increase and more widespread sale of clocks happened. Towards the end of the 17th and early 18th centuries clocks became more affordable.

As many will know as a result of the great book by Dava Sobel – ‘Longitude’, the problem of inaccuracy of clocks, was even more important at sea.

King Charles II founded the Royal Observatory in 1675 to solve the problems of Longitude of sea. The produced a Lunar method of telling time at sea. This could be inaccurate though and had many problems.

John Harrison

As a result in 1714, the British Government by Act of Parliament, gave a reward of £20,000 (a huge prize at the time) to solve the Longitude problem. John Harrison devoted his life’s work to solving this issue, and he produced various chromometers on display in Greenwich, London, these were called H1, H2, H3 and H4 dating from 1730 to 1760.

Longitude

These clocks were fantastic and clearly solved the problem. Harrison though was not part of the establishment at the time, he was a simple carpenter from Lincolnshire. It took him over 10 years to win his prize, and even then, only by the intervention of the King. Harrisons inventions led to the modern day ships chronometer, these were still widely used until the middle of the 20th century. His inventions led the UK to become an important sea power, and saved countless sailors lives.

Antique clocks were crucial in the 17/18th centuries both on sea and land. During the 18th century accuracy came to within a few minutes a week. It was not until temperature compensated pendulums and other regulator features on the movements, that happened in the latter part of the 18th century, that accuracy came to within a few seconds a week for these precision clocks.

The quest for the measurement of time was in effect solved. Time is central to everyones life, like it was with these great ancestors of ours. Many sayings are taken from these antique clocks, time flies , time shows the path of mans decay, all very morbid, but it is fact. We might have learnt how to measure time, but we can not slow it.

Nothing is so important as time, it is fundamental to life itself. We at Pendulum of Mayfair care for all aspects of antique clocks, please contact me at https://www.pendulumofmayfair.co.uk.

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Timekeeping – Clocks