Progress in precision The tourbillon and its evolution at Lange

Gravity is arguably the most elusive of all physical phenomena and has piqued the curiosity of the human mind since time immemorial. In H. G. Wells’ book “The First Men in the Moon”, which was published in 1901, an eccentric scientist named Cavor developed a mysterious material that cancels out gravitational forces. Unfortunately, or perhaps fortunately, gravitation can be neither neutralised nor deflected in the real world. One hundred years before Wells wrote his novel, watchmakers at least discovered a way to outfox gravity – with the invention of the tourbillon.

The tourbillon is probably the most elaborate horological complication for improving the rate accuracy of a mechanical watch. Patented in 1801, it was first integrated in pocket watches and later in wristwatches as well. To compensate for the influence of gravity on a possible centre of mass error of the balance, the entire escapement – the balance, lever, and escape wheel – is in a cage that rotates about the fixed fourth wheel once a minute.

The evolution of precision timekeeping instruments

The world’s first stop-seconds mechanism for the tourbillon

Timepieces endowed with a tourbillon kept the time very precisely, but there was a drawback: the tourbillon could not be stopped instantaneously, so it was impossible to set the watch with one-second accuracy. The patented stop-seconds mechanism for the tourbillon developed by Lange in 2008 made it possible for the first time to stop the device at will – regardless of the angular position of the balance and the orientation of the cage – with an arresting spring, thus allowing the time to be set to the second.

When the crown is pulled, a lever mechanism releases the stop lever, which guides the arresting spring in the direction of the balance. The contact pressure of the spring instantly stops the balance and with it the tourbillon cage.

Both spring ends are bent up to prevent jamming when the balance is arrested and released. When the crown is pushed home, the balance and the tourbillon are released. The watch instantly starts running again.

The V-shaped arresting spring engages with the tourbillon cage and the balance wheel rim when the crown is pulled out. This instantly stops the tourbillon and with it the movement as a whole.

At A. Lange & Söhne, all currently available models with a tourbillon are endowed with a stop-seconds mechanism – with one exception. The Tourbograph Perpetual “Pour le Mérite” has no seconds hand and thus needs no stop-seconds device.

Ralph Knoll on the stop-seconds mechanism for a Lange tourbillon