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atmos clock service

The Atmos clock has its own page because whilst it is still a torsion clock, it NEVER needs winding! Many of these clocks were long-service or retirement awards bearing an inscribed employee name plate. They also have a disc pendulum hanging from a fragile steel suspension that rotates very slowly in both directions (30 seconds each way for the Atmos, 7.5 seconds for the 400 day), and both are powered by a mainspring. But as the makers, Jaeger LeCoultre, say "With no battery, electric current or winding, the Atmos clock has been living on air since 1928".

The mainspring is kept wound by variations in temperature (not air pressure). A heavy coiled spring and an expanding bellows compete to create lateral movement. As the temperature falls, the bellows contract under the force of the heavy spring and this tiny movement is transferred to the mainspring via a small chain and a ratchet. As the temperature rises again the bellows expand against the force of the spring and this allows the ratchet to take up a few clicks, ready for the next temperature drop. A fall of 1 degree is said to add enough power to drive the clock for a day or more, and when fully wound, the mainspring is capable of running the clock for up to a year.

Originating in France, the first ones (later to become known as the Atmos Type I) were based on Jean-Leon Reutter's 1927 design which then used mercury and ammonia separated by cotton wool in a sealed 'U' shape glass tube, which rocked as the mercury was forced to one side by the expansion of the ammonia in the other side. CGR produced it from June 1929 under Reutter's management. Later, Jaeger LeCoultre of Switzerland became interested and in 1936 replaced the mercury in glass design with bellows (Atmos Type II). But the bellows had seal issues and production of the Type II was intermittent until 1939.

The Atmos Type III (calibres 519 and 529) in Image 1 was a lasting improvement and production ran until 1955 when the Type IV (calibres 522 and 523) appeared, still using the same bellows. But that was quickly replaced by the Atmos Type V (calibre 526) and then the Types VI, VII and VIII (calibre 528) seen in Image 2, which is the most common you will find. The whole Reutter influence disappeared with the launch of the Atmos calibre 540 (Image 3) when Jaeger LeCoultre stopped allocating Type codes.

The movement in the Atmos is finely engineered and unless interfered with suffers only from two problems on the whole. First, over the course of time mainspring grease becomes sticky and dirt gathers in the pivot holes, clogging them and thus impeding the rotation of the wheels. Stripping and cleaning usually solves this. I have never found any wear in the jewelled pivot holes so parts are rarely required. Setting upthe Atmos afterwards takes special tools and skill but once serviced, no attention should be required for ten years or more, though the 540 does seem to require servicing at more frequent intervals than the 526 and 528.

The other issue is with the Atmos bellows, which are made from thin stainless steel and the constant opening and closing can result in tiny stress cracks forming in the folds. The bellows, which are protected and concealed in a brass housing on the back of the clock (see Image 4) contain gaseous ethyl chloride, which boils at 54F (12.4C) so the pressure inside varies according to the temperature. If the gas leaks, like in the collapsed bellows shown on the left in Image 5, the clock might still keep running for months as the mainspring slowly unwinds but it will eventually stop.

If your bellows looks like the one on the left at room temperature, it needs attention; look at my page on Atmos bellows refill and repair for help. I know of no other repairer in the UK (possibly even all of Europe) offering this service but if you should know one please tell me.

Finally, the thin, delicate suspension from which the pendulum hangs sometimes breaks but this is usually the result of human interference - like moving the clock without first locking the pendulum.

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If you're looking for information on 400-day torsion clocks, you need to click HERE.



  • A less common Atmos Calibre 529.
  • An example of one of the most populat Atmos clocks, the Calibre 528.
  • The latest type of Atmos from Jaeger leCoultre, the Calibre 540
  • The bellows container on the back of the Atmos clock.
  • Collapsed bellows removed from an Atmos Calibre 528 movement, causing the clock to fail, compared to a good bellows at room temperature.