United States (Crane); Switzerland/France (Reutter, Atmos development) · Crane's patents c. 1840s–1850s; Reutter's Atmos-related work from the 1920s, industrialised by Jaeger-LeCoultre from 1936
Torsion Pendulum Clock Mechanism
Partially verifiedTorsion clocks (including 400-day 'anniversary' clocks) and the Atmos in particular are notable for extremely low power consumption and, in the Atmos case, essentially self-winding operation from ambient temperature change.
A torsion pendulum clock replaces the swinging pendulum with a weighted disc suspended on a thin wire or ribbon that twists and untwists, giving a very low rate of energy loss and long running times between windings.
Reutter's version, combined with a sealed bellows mechanism responding to small changes in atmospheric temperature and pressure to rewind the mainspring, became the basis of the Atmos clock manufactured by Jaeger-LeCoultre.
Background
The torsion pendulum clock was first invented and patented by American Aaron Crane in 1841. Robert Leslie invented the torsion pendulum in 1793, while Anton Harder independently patented a torsion clock in 1879-1880 after being inspired by a rotating chandelier. The mechanism functions by using a weighted disk or wheel suspended by a thin wire or ribbon known as a torsion spring.
Unlike an ordinary pendulum that swings, the torsion pendulum rotates around the vertical axis of the wire, which provides the necessary force to reverse the rotation. This configuration allows for extremely slow oscillation, resulting in very long intervals between windings, often lasting a year or more. The mechanism requires a stable environment and is typically shielded from air currents by a glass dome because it is sensitive to temperature-dependent elasticity in the spring.
Written from the encyclopedia entries listed under Sources; each statement was checked against the cited text.
How it works
- An escapement mechanism uses a crutch to apply pulses of torque to the top of the torsion spring to maintain oscillation.
- Adjustment screws on the pendulum allow the clock's timing to be modified by changing the moment of inertia of the weight balls.
- Suspension springs made of Nivarox, an alloy with a low thermal elasticity coefficient, are used to improve accuracy.
Later history
- Following the expiration of Harder's patent in 1887, several firms initiated mass production of these clocks in Germany.
- Charles Terwilliger of the Horolovar Co. developed a temperature-compensating suspension spring in 1951 to improve the timekeeping performance of these clocks.
How to verify this yourself
Crane's original US patents should be looked up by name and decade in the USPTO historical patent full-text/image database; Reutter's and Jaeger-LeCoultre's Atmos-related patents can be searched via Espacenet under 'Reutter' and 'Atmos' with 1920s–1930s date ranges.
Manufacturers known to have used it
- Jaeger-LeCoultre (Atmos)
- various 400-day anniversary clock manufacturers, chiefly German, 20th century
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- Torsion pendulum clock, Wikipedia (English), retrieved 2026-10-28 (text CC BY-SA 4.0)
- Jaeger-LeCoultre, published Atmos clock history
- USPTO historical archive (existence of Crane filings noted, numbers not independently verified here)
Where sources disagree, the disagreement is stated rather than resolved silently.