Remontoire is from the French word 'remonter' which means "to wind". It is a constant force device used in a timepiece whereby the main source of power periodically winds a spring or lifts a weight by equal amounts and at equal intervals to drive the timepiece's escapement. This device should not be confused with the term 'constant force escapement or remontoire escapement' which was discussed in the prior section on escapements. 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 operate. 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, through the wheel train and to its escapement. There are also the irregularities caused in the train by the release at intervals of the heavy striking and chiming trains, calendar or astronomical indicating mechanisms. Second is to supply a smooth, constant source of power to the escapement. Large seasonal temperature variances as well as environmental contaminants will cause differences in oil viscosity throughout the wheel train and is multiplied as the number of wheels and linkages increase. A remontoire alleviates this by isolating the escapement from the rest of the movement and keeping the number of wheels relevant in driving the escapement to a minimum.

Most tower clocks do not have a remontoire as this device added to the expense of manufacture and required more careful and experienced personnel to maintain. They are generally more fragile and subject to derangement than a simple going train movement. To overcome the above mentioned difficulties most makers went the route of brute force by employing heavier weights and robust wheel trains. An alternate, 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, and earlier type is the gravity style. It's invention is generally credited to by Jost Burgi, Swiss (b.1552 -1631), circa 1595 exhibited in his Experimental Clock No. 1. However, there is still some technical issue as to whether his clock has a true remontoire (1). He 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. This type uses a small weight to drive the escapement indirectly, usually the next wheel, but direct escape drive is known. The second is spring style. This is reliably credited to Jost Burgi in his Experimental Clock No. 2, c. 1597. Here a small subsidiary spring is used as the motive of power to the escapement which, in turn, is kept wound at frequent intervals by the main movement spring. In tower clocks that spring is rewound by the clocks weights. The subsidiary spring is normally attached directly to the escape wheel in tower clocks, but may be further down the train in smaller movements such as was the case in Burgi's clock.

Each of these styles can operate either on the wheel train (usually the wheel next to the escapement wheel); called a train remontoire or directly upon the escapement wheel; called an escapement remontoire. The latter not to be confused with remontoire escapements which are escapements in and of themselves. However in the majority of cases where employed in tower clocks 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 time weight or occasionally by the striking train. The remontoire has also been used in some domestic 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, usually a Robin type, effectively combining a spring driven clock and its advantages of portability, with a weight driven clock and its advantage of a constant force of gravity; in addition to isolating the escapement from the rest of the movement. Alternatively a fusee was commonly used to overcome the spring problem. It was much simpler and cheaper but not quite as accurate.

A clock equipped with a remontoire is fascinating to observe, as there is a periodic movement of the rewind mechanism and this is usually mediated by a fly fan a.k.a. an air brake that spins around. The cycle can vary from as little as one second (rarely found and then only in watches) to one minute or more. The most common being 30 seconds and one minute.

Footnote (1). I have not been able to get details of the movement and remontoire of Burgi's Experimental Clock No. 1. From what I have been able to determine Burgi's remontoire does not supply power to the escapement during the rewinding phase of the remontoire weight. During my visit in 2014 to the Mathematish-Physikalischer Salon at the Zwinger Palace in Dresden, Germany where this clock is displayed, my suspicion was confirmed by museum personnel. A true remontoire must supply power consistently through both the deployment and rewind phases. Burgi's remontoire was rewound once daily by the clock's mainspring and is very large for a remontoire weight. Technically if that weight could be rewound and deployed within the period one tick of the clock's cross beat escapement then the requirement for power during rewinding would be unnecessary. Since the cross beat was seconds beating, this would require the rewinding of this large weight to occur in less than one second. Because of the great importance and antiquity of this artifact, the museum will not run the clock so it is impossible to determine the speed of the weight's ascension during rewinding. But having seen the remontoire weight I find it difficult to believe it was done in under one second.