A remontoir is a small extra power source, such as a weight or a spring, that drives a timepiece’s timekeeping part and is wound up again from time to time by the main power source. It sits between the power source and the escapement. Its job is to give the regulating organ a steady force.
How does a remontoir work?
The mainspring does not drive the escapement directly. Instead, it rewinds a secondary spring at intervals and then releases it. Between rewinds, that secondary spring is the only thing driving the escapement. The regulating organ receives its force from the small spring alone, so the force stays even. Remontoirs are built to rewind often. Depending on the design, this can be anywhere from once a second to once an hour.
Where it comes from
The name comes from the French verb remonter, to wind. The Swiss clockmaker Jost Bürgi invented the gravity remontoir around 1595, using a weight as the extra power source. The English clockmaker John Harrison invented the spring remontoir in 1739, while he was developing his H2 marine chronometer. Abraham-Louis Breguet used remontoirs in his clocks, but not in his watches. In turret clocks, a remontoir keeps the large force needed to turn the hands apart from the small force the escapement needs.
Can a wristwatch have a remontoir?
Yes, but only the spring type. A weight would not work, because the movement of the watch would disturb its pull. Andreas Strehler has made a wristwatch remontoir d’égalité. In it, the energy reaching the seconds wheel depends only on a hairspring in the intermediate winding mechanism. This makes it practically independent of the barrel, the part that holds the mainspring.
Not to be confused with
A remontoir is not a maintaining power spring. A maintaining power spring only keeps the timepiece running while it is being wound. A remontoir drives the escapement between each of its rewinds. The word also causes confusion on old pocket watches. After 1860, many French and Swiss pocket watches had Remontoire stamped on the back. This only meant they were wound by a crown. It does not mean they have a true remontoir.
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