The Atmos is a mechanical table clock with rotating pendulum, where the spring is wound using the thermal expansion of a suitable liquid. With pieces from 1945, ethyl chloride, which is strongly responsive to temperature changes, is used as a liquid. This liquid exerts its power when the temperature changes in a can.
The system of an auto-dynamic watch was presented already by Friedrich Ritter von Lössl in 1880 to the public, who for this received a patent from the Imperial Patent Office. After the Swiss engineer Jean-Léon Reutter had developed the first prototype of a table clock, which draws its energy from the smallest atmospheric changes, in 1928, he obtained a French patent in 1929.
After the first pieces were manufactured in France, the Swiss watches manufacture Jaeger-LeCoultre from 1945 produces the modern version of such a watch and offers it under the name "Atmos". This watch gets its driving energy for the winding of the spring from the weather-related fluctuations in temperature, which are sufficient to keep the movement going even in well air-conditioned rooms. The impressive balance wheel moves in only two vibrations per minute with majestic slowness. The Atmos system reacts very sensitively: A change in temperature of 1°C is sufficient for an operating time of about 48 hours. Switzerland presents the "Atmos" as an official state gift.
The ethyl chloride is enclosed in a metal housing, which thanks to its bellows shape acts as an expansion chamber. When the temperature rises, the ethyl chloride gas expands. The chamber expands like an accordion and presses together a spring, which acts as a counterweight and is fully compressed at 27° Celsius. In this procedure, a small chain rolls around a small drum. Another small spring ensures the pull. With decreasing temperature, the chain unwinds again, the drum snaps and thereby drives the shaft of the drive spring. This spring is wound and thus saves the necessary drive energy. The precise calculation of the ratios makes it possible to keep the number of gears as low as possible to reduce the friction. The 240-gram balance wheel is actually a torsion pendulum and hangs on a thin Elinvar wire. Therefore it needs a hundred times less energy than a wristwatch! Thanks to this constant energy the exact rate of the Atmos is guaranteed.
The success of the Atmos
The Atmos has become one of the great successes of Jaeger-LeCoultre. Especially in the US, many of these watches were sold. 1978 the number of produced models already exceeded the figure of 500,000. Meanwhile, there are a number of variants, including the Atmos 3000, which displays not only hours and minutes, but also the moon phase, or the luxury version "Joaillerie", whose prismatic case is made entirely of crystal glass. With the limited model "Régulateur" the display is based on the regulator principle and the hours and minutes are shown on separate dials made of solid silver.