A tall wooden longcase clock in a quiet hallway with wooden floorboards, its brass pendulum bob visible through a glass panel in the trunk
AI-generated image, not a photograph of a real person or place.
theocl

AN INFORMATIONAL GUIDE: OLD CLOCK LORE

One swing,
one second.

TICK once a second

  • The pendulum sets the pace
  • The escapement lets it go
  • The weights keep it going
  • Three parts, steady time

A pendulum of just over 39 inches beats once a second.

Here OCL stands for old clock lore: this is an independent informational guide, not an organisation. The pendulum turned clocks from rough guides into instruments, and gave homes the tall longcase or grandfather clock.

Updated

Caring for a clock

THE SHORT ANSWER

How a pendulum
keeps time.

The Metropolitan Museum of Art explains why
the pendulum changed European clocks.

THE PENDULUM

A built-in beat

Unlike earlier controls, a freely swinging pendulum has a definite period of its own. Huygens made the first pendulum clock design at the end of 1656.

See the numbers

THE ESCAPEMENT

Letting time out

The anchor escapement allowed a long pendulum with a small swing, giving a one-second beat and a seconds hand without complicated gearing.

A short history

CARE

Wind it the same way

Conservators advise winding gently, steadily and fully, at the same time of day for 30-hour clocks or the same day each week for 8-day clocks.

Caring for a clock

CARING FOR A CLOCK

Can you do it,
or call someone?

Pick a task. The bar shows how strongly the Institute of Conservation's guide points to a professional horological conservator.

Clock care

Choose a task
Winding an 8-day longcase clockOwner's job

Use a well-fitting crank key, wind on the same day each week, and wind gently so the weights do not bang the underside of the clock.

Making it run faster or slowerSmall turns

Stop and support the pendulum, then turn the rating nut: right raises the bob and speeds the clock. Make half turns and wait two or three days.

Putting the time back an hourStop, do not reverse

Never turn the hands backwards without advice. Stop the clock and restart it when the real time catches up with the dial.

Oiling the movementProfessional

Lubricants deteriorate: the guide suggests re-oiling every three years and a full clean within five to eight, by a professional. Do not use household oils.

Source: Icon, the Institute of Conservation, Clocks collections care guide.

Based on Icon (the Institute of Conservation), Clocks: collections care guide. Every clock is different; ask a conservator if unsure.

TWO NUMBERS WORTH KNOWING

Seconds pendulums
and year-long clocks.

One figure from the Met's essay,
one from a Greenwich clock.

39 in +

Length of a seconds pendulum

A pendulum of slightly more than 39 inches beats once a second. The longcase grew up as the case to protect that pendulum and the weights.

PENDULUM · THE MET

13 ft

Pendulum of a 1676 Greenwich clock

Tompion's year-going clock for the Royal Observatory hung its pendulum behind the panelling. It helped Flamsteed show the Earth's rotation was constant.

OBSERVATORY · RMG

A Royal Society record of 1736 describes the same clock as going thirteen months without winding.

FOUR STEPS IN THE STORY

From Galileo
to the grandfather.

A hand turning a brass winding key in the winding hole of an old hand-painted clock dial
AI-generated image, not a photograph of a real person or place.

Drawn from the Metropolitan Museum of Art and Royal Museums Greenwich.

  1. Galileo spots the principle

    The Met credits Galileo with discovering the principle of the pendulum, and Huygens with turning it into a clock in 1656.

  2. London catches on

    A London clockmaking family sent a son to learn in the Hague, and by November 1658 was advertising pendulum clocks in London.

  3. The longcase arrives

    The anchor escapement and a seconds pendulum needed a tall case to stand on the floor: the longcase, or grandfather clock.

  4. Clocks for astronomers

    By the end of the 1600s, clocks were accurate enough for astronomy, including Greenwich's year-going clocks of 1676.

KEEP IT HAPPY

Where to keep
an old clock.

Close view of an old brass clock movement with interlocking toothed wheels and a steel escapement
AI-generated image, not a photograph of a real person or place.

Icon advises against placing a clock near any heat source, including strong sunlight or a mantel over a working fire, and suggests stopping a pendulum clock before going on holiday.

Pendulum clocks are not self-starting: move the pendulum about a centimetre to one side and let go. If it does not tick, try a little further, but not too far. Longcase and wall clocks should also be fixed securely to a wall, Icon says, both for safety and so that they run properly.

Questions

Questions people ask

What does OCL stand for here?

Old clock lore. This is an independent informational guide, not an organisation, shop or repairer.

Why does a pendulum keep good time?

A freely swinging pendulum has a definite period of its own, which the Met says made it far better than earlier controlling devices.

Why are grandfather clocks so tall?

To house a seconds pendulum of slightly over 39 inches and the driving weights, according to the Met's account of the longcase.

Can I over-wind a clock?

Icon says there is really no such thing as over-winding, but winding roughly or suddenly can cause expensive damage. Count the turns as a guide.

How often should an old clock be serviced?

Icon suggests re-lubrication every three years and a full professional clean after five years, and no longer than eight.

Why did the Royal Observatory need such accurate clocks?

Sir Jonas Moore commissioned two clocks from Thomas Tompion after the observatory was founded in 1675, so that John Flamsteed, the first Astronomer Royal, could accurately record the motions of the planets and the Moon and help fix the positions of stars. Royal Museums Greenwich says the clock's accuracy let Flamsteed establish that the Earth rotates at a constant speed, which was fundamental to finding longitude at sea. Their escapement was the deadbeat, invented by Richard Towneley and made and modified by Tompion, the Royal Society notes.

How should I set the hands on an old clock?

Gently and slowly, using only the minute hand; Icon says never to move the hour or seconds hands. Let a striking clock finish striking before moving on, and avoid moving the hands more than an hour or so forward: for a bigger change, stop the clock and restart it when the time matches the dial. Try not to touch the dial, as moisture and grease from fingers can damage it.

Sources

Where the facts come from

  1. The Metropolitan Museum of Art: European clocks in the seventeenth and eighteenth centuries
  2. Royal Museums Greenwich: Year-going clock by Thomas Tompion, 1676
  3. Royal Society blog: Flamsteed observed
  4. Icon, the Institute of Conservation: Clocks collections care guide

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