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I was asked to post some details on the Atmos mechanism, so here goes. Many of you will have heard of the Atmos – Jaeger Le Coultre’s famous clock, but you may not be aware of what makes it so special. This is a mechanical clock that rarely, if ever needs to be wound. No, it hasn’t solved the problem of perpetual motion, but it is unique.

For those who don’t know what the Atmos looks like, JLC’s home page for it is here - http://www.jaeger-lecoultre.com/na/en/w ... -classique

The clue is in the name, Atmos – the clock is wound by changes in temperature and atmospheric pressure. There are a couple of different concepts, and the success of the Atmos is dependent on both working well. The first is the reduction of friction to as much as possible.

As a result the traditional clock pendulum (the equivalent of a balance spring in a mechanical watch) is replaced with a torsion pendulum. Unlike the traditional pendulum that swings back and forth, a torsion pendulum rotates back and forth in a circular manner – they’re fairly common in desk / table / mantle clocks as they take up less space, but more importantly for the Atmos they also consume a lot less energy than a traditional pendulum. Atmos takes it further by oscillating the pendulum only twice per minute (as opposed to 120 times a minute for a conventional clock).

The second concept is that of expansion and contraction, and here’s where the science starts. We all know that things tend to expand when heated and contract when cooled, and we also know that things tend to compress under pressure and expand when that pressure is removed. The susceptibility of a material to expand or contract / be compressed will depend on the nature of the item – what it’s made of, how dense it is, etc.

A quick note - I can’t find any copyright free pictures, so forgive the lack – you can Google and find some, but as admin is looking to post this technical series on the main pages I am going to avoid using copyrighted pictures. I’ll keep looking, or maybe draw something myself.

In the back of an Atmos clock is an airtight chamber made of brass. Inside that chamber is a bellows unit, and inside the bellows is a spiral spring. That spiral spring is connected to the mainspring of the clock through a pulley and chain system. The movement of the spiral spring is what causes the mainspring to wind – the same function that a rotor fulfills in an automatic watch. The magic is in what causes the spiral spring to move.

Inside the airtight chamber is a material called chloroethane, or ethyl chloride (same material, different names). This has had a number of uses in the past, but today I believe that it’s only commonly used in making paint. It is also a narcotic drug!

The property that makes it of use in these clocks is that it boils at around 12 degrees Celsius (54 degrees Fahrenheit). That means that at normal atmospheric temperatures it expands and contracts dramatically with only small changes in temperature. As a result, as the temperature of the room that the clock sits in rises, so the chloroethane expands and compresses the spiral spring. When the temperature drops the chloroethane contracts and the spiral spring expands. Changes in atmospheric pressure have the same (though less pronounced) effect.

To put this in perspective, a change of just one degree Celsius (1.8 degrees Fahrenheit) causes enough movement in the spiral spring to wind the mainspring enough for the watch to run for around 48 hours.

Just a brief note on the history of these. JLC didn’t invent the Atmos, they were first produced by a Dutchman named Cornelius Drebbel in the early 1600s. He wasn’t a clockmaker by trade, rather he was an inventor who focused much of his work into telescopes and microscopes as well as thermometers and temperature regulators (though he also invented a submarine!). The temperature work led to the production of the clocks.

The concept never really caught on although they were produced in the 1700s and 1800s by a couple of different people. They started commercial production at the end of the 1920s by a French company (CGR) using mercury and ammonia. JLC bought the production rights from that company and then updated the design.

As always, feedback is appreciated, as are requests for topics for more articles!

Another great article, Roff.
Thanks for explaining how that beauty runs.

thanks roff, very interesting! technology these day never seizes to amaze me.

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Emergency
Bentley GT
Chrono Colt
Avenger Skyland Blacksteel
Steinhart LE#9/15

Another fabulous article Roff.

It was interesting to learn of the use of ethyl chloride in these clocks. I use it on a daily basis in my medical practice as a topical skin anesthetic prior to hypodermic injection. It is released from a small pressurized bottle in a fine spray whereby once it reaches atmospheric pressure it boils to the vaporization point. Once in contact with the skin the conversion from the liquid to the gas state or "heat of vaporization" , absorbs the heat from the skin, causes a freezing effect, resulting in temporary numbing of the superficial cutaneous nerves of the skin.

Thanks so much for these articles Roff. I look forward to each and every one and they are one of my favorite reads on this site.

Since I was the one asking for this topic, I will give you a big THANK YOU

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Blue Baton Super Avenger
Black Avenger Seawolf

Excellent Roff, and the timing is impecable for me. After aquiring a Panerai wall clock (my grail wall clock due to the design and lume) I am now on the hunt for a JLC Atmos clock, yoru just fueling my need for one

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Certified watch nut.

That is fascinating Roff, great article! Brilliant engineering to even think of the science and then apply it to a timepiece.

Fantastic read, as always thanks for taking the time. I always look forward to reading a new article!

Will let you know if I think of anything

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Happines is Good Health and a Bad Memory.
"Ingrid Bergman"

Nicely written as usual Roff, and as my father owns an Atmos, I can confirm that you are entirely correct in your information!

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Driver8

Site Moderator

Thanks guys.

Wasn't aware that chloroethane was used in medicine these days, the biggest use until 20 years or so back was in making anti-knock additives to gasoline.