A brief discussion on remontoire below; and for further information, examples, pictures and drawings of different remontoire access the author's lecture notes.
This movement employs a gravity driven train remontoire. A remontoire, from the French word 'remonter' (to wind), is a constant force device used in a timepiece whereby the main source of power periodically winds a spring or lifts a weight to drive the timepiece's escapement. A train remontoire is employed beyond the actual escape wheel - usually the next wheel down the going train. This arrangement normally employs a gravity driven remontoire. The purpose of a remontoire in a tower clock is two fold. First is to mechanically isolate the escapement from the rest of the movement. This prevents variations and stoppages that might occur due to the environment that a tower clock must work in. Wind and weather such as ice and snow acting upon the large clock hands on the outside of the tower will be transmitted back through the linkages toward the movement and its' escapement. The second is to supply a smooth, constant source of power to the escapement. Large seasonal temperature variances will cause differences in oil viscosity throughout the wheel train and is multiplied as the number of wheels and linkages increase. A remontoire keeps this number to a minimum by providing a power source close to the escapement independent of the rest of the movement rain. Most tower clocks do not have a remontoire as this device added to the expense of manufacture and required more careful and experienced people to maintain. Nearly all makers chose to overcome the the above mentioned difficulties by brute force; employing heavier weights and robust wheel trains. An alternative, but less elegant solution.
Remontoire come in a wide variety of mechanical styles, and complexity. They can generally be divided into two categories. The first is the spring style; where a small spring is used as the motive of power to the escapement. This is normally attached directly to the escape wheel. The second is a gravity driven style where a small weight drives the escapement usually from the next wheel down the train from the escapement. Each of these styles can operate as a train or escapement type. However in the majority of cases gravity remontoire operate as train remontoire and spring remontoire operate as escapement remontoire. Both spring and weight styles are periodically rewound or lifted by the main weight or spring of the clock movement. This device has also been used in some clocks to overcome the problem of diminishing power being delivered to the escapement as the main spring unwinds. The main spring will drive a gravity remontoire effectively turning a spring driven clock with its advantage of portability to a weight driven clock with its advantage of a constant force of gravity. In addition are the advantages of isolating the escapement from the rest of the movement. Alternatively, a fusee was commonly used to overcome the spring problem, and was much simpler and cheaper but not quite as accurate. Nor as interesting to watch!
The gravity remontoire was invented c. 1595 by Jost Burgi, Swiss (1552-1631) and is also known for his invention of the cross-beat verge escapement. These innovations made his clocks the most accurate mechanical timekeepers of their day. The second class of remontoire, the spring driven type, was invented by John Harrison during development of his H2 marine timekeeper in 1739. This, in conjunction with other innovations in his H4 model of a ships' chronometer, won him the Longitude Prize in 1773.
A clock incorporating a remontoire is actually supplying power split between two mechanisms. One is constant - the remontoire supplying the escapement. The other is periodic and only operates to rewind the remontoire and advance the clock hands forward. Click here to view an animation.
Other examples of the Bernard Henri Wagner train remontoire are found in the Dent exhibition clock and Collin-Wagner master clock both in the skeleton clock section. Other gravity driven train remontoire are exemplified by the differential remontoire in the Korfhage 3 train, Korfhage two train, Schneider and Horz and an alternative form of differential in Borrel-Wagner. A Robin endless chain style gravity remontoire is illustrated in another Horz. Other examples of gravity driven remontoire are found in the Perrot and Addicks. An unusual gravity driven escapement type is in Seybold.
The other main type of remontoire, the spring driven escapement remontoire, is illustrated by the Schwalbach. Also the Dent, Concord in the skeleton clock section. The Denison style double -three-legged gravity escapement is also a type of escapement remontoire as are many others such as Hardy's spring escapement, (detailed in lecture notes).
A movement equipped with a remontoire is fascinating to watch, as there is a periodic movement of the rewind mechanism usually mediated by a fly fan (air brake) that spins around.
For many more pictures of this tower clock and it's step by step restoration process, go to the beginning of this web site's home page and click on the "Tower Clock Restoration Page" picture, or just click here.