Pendulum clock

A pendulum clock is a clock that uses a pendulum, a swinging weight, as its timekeeping element. The swinging motion of the pendulum helps the clock keep very accurate time because it swings in a steady rhythm based on its length. This idea was first thought of by Galileo Galilei around 1637, but the first actual pendulum clock was made later in 1656 by Christiaan Huygens, who was inspired by Galileo’s observations.

From the time it was invented until the 1930s, the pendulum clock was the most accurate way to tell time in the world. Because of this, pendulum clocks became very important in homes, factories, offices, and even railroad stations. They helped people keep track of time for work, travel, and daily life. The better accuracy of these clocks helped speed up many parts of life, which was very important during the Industrial Revolution.

Even though pendulum clocks were very useful, they needed to stay in one place to work right. If they moved or were shaken, the pendulum would not swing properly and the time would be wrong. Because of this, other kinds of clocks were used when people needed clocks that could be carried around easily.

In the 1930s and 1940s, pendulum clocks were mostly replaced by newer kinds of clocks called synchronous electric clocks, which were cheaper and easier to use. Today, pendulum clocks are usually kept because they look beautiful and are interesting antiques, but they are not used much for telling time anymore.

History

The first pendulum clock was invented by Christiaan Huygens in 1656. He was inspired by the work of Galileo Galilei, who discovered that pendulums swing in a regular way, making them perfect for keeping time. Before pendulum clocks, clocks were not very accurate, losing up to 15 minutes a day. But with the pendulum, accuracy improved greatly, to just 15 seconds a day.

Pendulum clocks became very popular because they were much more accurate. They were used everywhere, from homes to train stations. Even for keeping very exact time, special pendulum clocks were used in places like observatories. Pendulum clocks stayed the best way to keep time for over 270 years, until new technology like quartz clocks was invented in the 1920s.

Mechanism

A mechanical clock's inner workings are called its movement. All mechanical pendulum clocks have five main parts:

• A power source, like a weight on a cord or a mainspring.
• A gear train that changes the power's speed so the pendulum can use it. The gears also slow down the movement to turn the clock hands correctly.
• An escapement that gives the pendulum small pushes to keep it swinging and lets the gears move forward a little bit each time. This is what makes the clock tick.
• The pendulum, a weight on a rod, which decides how much time passes.
• A dial that shows the time, usually a clock face with moving hands.

Some clocks have extra features besides just telling time:

• A striking train that hits a bell or gong to show the hour. Some even play melodies or sounds like church bells.
• Calendar dials that show the day, date, and sometimes the month.
• A moon phase dial that shows the moon's shape, which helped people plan night trips long ago.
• An equation of time dial that shows how the clock's time differs from the sun's time, which changes during the year.
• A repeater that lets you hear the hour chimes when you press a button, useful before electric lights.

In electromechanical pendulum clocks, electricity powers a solenoid to push the pendulum, and a switch or photodetector checks the pendulum's position. These are different from quartz clocks, where a quartz crystal controls the time and the pendulum just moves for show.

Gravity-swing pendulum

The pendulum inside most clocks is made of a rod with a metal weight, called the bob, on the end. The bob is shaped like a lens to cut down on air resistance. Wooden rods were often used because wood changes less with temperature than metal. The rod is held up by a thin spring to keep it steady.

A part called the crutch pushes the pendulum to keep it swinging. Each swing helps move the clock's hands. Many clocks, like grandfather clocks, have a seconds pendulum, which swings once each second. Smaller clocks might have faster pendulums.

The time it takes for the pendulum to swing depends on its length. Adjusting the bob up or down changes the pendulum’s length and helps set the correct time. Even small swings keep the time very steady.

Temperature compensation

Temperature can change the length of the pendulum rod, making the clock run faster or slower. Early clocks used mercury in the bob to balance this out — when the rod expanded with heat, the mercury also expanded, keeping the pendulum’s swing just right.

Later, a gridiron pendulum used rods of different metals that expanded and contracted to cancel each other out. Some very precise clocks used special materials that hardly changed with temperature at all.

Atmospheric drag

Air can slow down the pendulum, so the bob is shaped to cut through the air easily. Some very exact clocks were placed in special cases with less air to keep them running smoothly.

Leveling and "beat"

For a clock to keep good time, it must be level. If it leans, the pendulum swings unevenly, which can make the clock stop. Listen for an even “tick...tock...tick...tock.” If it sounds uneven, the clock needs to be leveled.

Local gravity

The pull of gravity changes depending on where you are on Earth. Moving a very exact clock even a little — like to the top of a tall building — can change the time it keeps. These clocks need to be readjusted after moving to stay accurate.

Torsion pendulum

Main article: Torsion pendulum clock

A torsion pendulum clock uses a special wheel-like mass, often made of four spheres on cross spokes, hanging from a thin strip of spring steel. This setup helps control the time in torsion pendulum clocks. When the mass turns, it winds and unwinds the spring, giving the clock its energy. The big advantage of this type of clock is that it uses very little energy. With a swing time of 12 to 15 seconds (compared to the 0.5 to 2 seconds of regular pendulum clocks), these clocks might only need winding once every 30 days, or even once a year or more!

Because the spring’s strength can change with temperature, these clocks can be affected by temperature changes more than regular pendulum clocks. The most accurate ones use a special spring made of elinvar, which changes very little with temperature.

A clock that only needs winding once a year is sometimes called a "400-Day clock" or "anniversary clock", and is often given as a wedding gift. Torsion pendulums are also used in clocks that never need winding, called “perpetual” clocks. These clocks use changes in air temperature and pressure to keep their mainspring wound, with a special bellows arrangement. The Atmos clock is one example, using a torsion pendulum that swings once every 60 seconds.

Escapement

Main article: Escapement

The escapement is a special part in a pendulum clock that helps keep time. It takes the power from the clock’s moving parts and gives small pushes to the pendulum to keep it swinging. This is what makes the ticking sound in a working pendulum clock.

Over time, different designs of escapements were made to improve accuracy. One common design, the anchor escapement, was used for many years. Later, an even better design called the deadbeat escapement became standard in precise clocks. Some special clocks used other types of escapements to make sure they kept very accurate time.

Time indication

Most pendulum clocks show the time using a traditional dial with hour and minute hands that move. Many also have a small third hand that shows seconds on a smaller dial. To set the time, you usually open the glass cover on the front and turn the minute hand to the right spot. Turning the minute hand also moves the hour hand to the correct time.

Maintenance and Repair

Pendulum clocks last a long time and do not need much care, which helps explain why many people like them.

Like any moving machine, they need regular cleaning and lubrication. Special lubricants that are thin and smooth are used for clocks, and one common type is a synthetic oil. Over time, springs and pins can get worn out or break and need to be replaced.

Styles

Pendulum clocks were not just tools for telling time; because they were expensive, they showed off the wealth and culture of their owners. Over time, these clocks developed many different styles, depending on where they were made and when. The design of their cases often matched the popular furniture styles of the time. Experts can guess when an antique clock was made by looking closely at its case and face.

Some of the many styles of pendulum clocks include:

• Act of Parliament clock
• Anniversary clock (uses a torsion pendulum)
• Banjo clock
• Bracket clock
• Cartel clock
• Comtoise or Morbier clock
• Crystal regulator
• Cuckoo clock
• Grandfather clock
• Lantern clock
• Mantel clock
• Master clock
• Ogee clock
• Pillar clock
• Schoolhouse regulator
• Torsion pendulum clock
• Turret clock
• Vienna regulator
• Zaandam clock