Skip to content
The Encyclopedia of Horology

Clock type · Precision

Atmos-Type Perpetual (Pressure-Driven) Clocks

Partially verified

A class of mantel clock wound automatically by small changes in atmospheric temperature and pressure acting on a sealed capsule of expanding gas, rather than by a mainspring or falling weight, most closely associated with the Jaeger-LeCoultre Atmos clock.

Movement & mechanism

  • A hermetically sealed bellows or capsule containing a gas (historically mercury-vapour based mixtures, later ethyl chloride) expands and contracts with small changes in ambient temperature
  • This slight mechanical movement winds a mainspring via a chain of levers over each temperature cycle, requiring no manual winding under normal conditions
  • Because available driving power is extremely small, the movement runs on a torsion pendulum (a rotating balance suspended on a fine ribbon) rather than a swinging pendulum, since torsion escapements require far less energy
  • Very low power transmission demands exceptionally low-friction jewelled bearings throughout the train

Identification

  • Glazed case on all sides, allowing the torsion pendulum's slow rotating motion to be seen
  • No winding hole, key or crown, since the movement is designed to be wound by ambient conditions alone
  • Absence of a conventional swinging pendulum; instead a horizontal balance wheel rotates slowly back and forth

Terminology

  • Torsion pendulum — a balance suspended on a twisted wire or ribbon that oscillates by unwinding and rewinding rather than swinging
  • Perpetual motion clock (a misleading but common trade description) — in fact powered by ambient temperature/pressure change, not a true perpetual-motion device

Known variations

  • Standard time-and-date Atmos clocks
  • Complicated Atmos clocks with moonphase or perpetual calendar displays
  • Earlier, non-Jaeger-LeCoultre atmospheric-powered clocks from the 1920s–1930s patent era

Collecting notes

Atmos clocks are extensively collected, particularly Jaeger-LeCoultre production, with case design, serial numbering and complications (such as calendar or moonphase dials) all bearing on interest; because the type depends on a sealed capsule that can fail or be serviced, mechanical originality of the capsule assembly is a significant conservation consideration.

Related photographs

Haller torsion pendulum anniversary clock
Haller torsion pendulum anniversary clock — Graham Evans, Battersea Clocks Home (aka westminsterclocks), CC BY-SA 2.0. Wikimedia Commons file page
Anniversary Clock, made by Ferguson's Watch and Clock Shop, Walpole MA, undated - Bennington Museum - Bennington, VT - DSC08665
Anniversary Clock, made by Ferguson's Watch and Clock Shop, Walpole MA, undated - Bennington Museum - Bennington, VT - DSC08665 — Daderot, Public domain. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. Rawlings, A. L., The Science of Clocks and Watches
  2. Individual patent priority and precise mechanism dates for early atmospheric-driven clocks are not verified here.

Where sources disagree, the disagreement is stated rather than resolved silently.