December 25, 1656

Pendulum clock

Huygens makes his first pendulum-clock model

The Christmas Day date survives only because, a year later, Huygens wrote that 'yesterday' had been exactly the anniversary of his first model.

25 December 1656, by the inventor's own reckoning

Christiaan Huygens stated retrospectively that he made the first model of his new kind of clock on 25 December 1656 in the Dutch Republic.

The evidence is a letter he wrote to the astronomer Ismaël Boulliau on 26 December 1657, saying that 'yesterday' had been exactly one year since the first model. No contemporaneous notebook entry independently confirms the day.

A pendulum joined to an ordinary escapement

The mechanism coupled a pendulum to a conventional clock escapement, letting the pendulum's regular oscillation regulate the clock.

'First model' does not reveal how complete, durable, or accurate that Christmas Day mechanism was. Good pre-pendulum verge-balance clocks typically erred about fifteen minutes a day; NIST gives less than a minute a day for Huygens's early clock, and peer-reviewed work about 10 to 15 seconds for refined Huygens-era examples.

Nothing public happened that day

The surviving evidence establishes no public demonstration, announcement, patent, or commercially manufactured clock on 25 December.

During 1657 Huygens engaged the Hague clockmaker Salomon Coster, who built the earliest surviving examples and received the sole right to manufacture his clocks.

The pendulum clock transformed stationary timekeeping, but not navigation: on a pitching ship the pendulum was unusable, and marine longitude waited for later chronometers.

Sources

Researched 24 Aug 2026 6 sources not yet audited Traditional date

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Traditional date. This date is the conventional one, not one fixed by a contemporary record.

What the sources leave uncertain

The exact day rests on Huygens’s recollection in a letter written one year and one day later; no contemporaneous notebook entry consulted independently confirms 25 December.
The phrase “first model” does not reveal how complete, durable or accurate that Christmas Day mechanism was.
Accuracy figures apply to early or well-tuned Huygens pendulum clocks generally, not demonstrably to the first model made on 25 December.