The Atmos clock has its own page because whilst it is still a torsion clock, it's uniquely like perpetual motion. Both have a disc pendulum hanging from a thin steel strip 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 the difference is that the Atmos never needs winding. As the makers, Jaeger LeCoultre, say "With no battery, electric current or winding, the Atmos clock has been living on air since 1928".
Its reliance on atmospheric change is what gives the Atmos its name: the mainspring is kept wound by variations in temperature and (to a lesser extent) air pressure. A heavy coiled spring and an expanding bellows compete to create lateral movement. As the temperature rises, the bellows expand against the force of the spring and this tiny movement is transferred to the mainspring via a small chain and a ratchet. As the temperature falls the bellows contract under the force of the spring and this allows the ratchet to take up a new position ready for the next temperature increase. A rise of 1 degree will add enough power to drive the clock for 2 days, 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 a mercury in glass system, which rocked as the mercury expands. 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 better and production ran until 1955 when the Type IV (calibres 522 and 523) appeared, 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. Many of these Jaeger LeCoultre clocks were long service and retirement awards bearing an inscribed employee name plate. 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, 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 appreciable wear in the jewelled pivot holes so repair is rarely required. Setting the Atmos up afterwards takes special tools and skill but once serviced, no attention should be required for ten years or more.
The other issue is with the Atmos bellows, which are metal 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 liquid and gaseous ethyl chloride, which boils at 54F 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 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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