With Urban Jürgensen blank Certificate, original fitted wooden presentation box with cream ostrich-leather lining.
The present tourbillon is the creation of Urban Jürgensen & Sønner whose master watchmaker Derek Pratt worked on such timepiece for over 4,000 hours. According to research, only five of these extremely rare movements featuring the possibly first tourbillon incorporation a remontoire within, instead of under, the carriage of a watch, were made. One was fitted with a platinum case, one with a pink gold case and three with yellow gold cases.
The timepieces possibly also house the smallest ever remontoire, a device aimed at maintaining a constant supply of force to the escapement, thus increasing its accuracy. The construction of the tourbillon follows the work of celebrated watchmakers, past and present, such as the English master watchmaker George Daniels who mounted a remontoire under a carriage.
While the first tourbillon invented by Abraham Louis Breguet around 1795 had a revolving period of one minute, others were later developed with periods of anything from about one minute to around one hour.
The present one-minute tourbillon indicates full dead beat seconds and is equipped with a carriage-mounted remontoire, twin mainspring barrels and power reserve. The inscription "Invenit et Fecit, Derek Pratt, 1897" on the bridge of the movement was hand-etched by Pierre Matthey.
Remontoires are designed to compensate for variations in the driving force and power transmission which can result in fluctuations in the impulse delivered to the balance. The one-second remontoire fitted within the carriage of the present timepiece (and which is concentric with the escape wheel) ensures that the carriage advances once each second while the remontoire rewinds. As a result, the seconds hand beats full seconds. The remontoire itself is of the Barbezat-Bôle type which does not "trip". The use of two barrels meanwhile provides a gentle deceleration of the tourbillon carriage.
Such tourbillon construction achieves several results: it ensures constant amplitude of the balance in a vertical position of 220 degrees, irrespective of any fluctuations in the torque applied by the mainsprings, errors in the gear train or lack of poise in the carriage. Furthermore the seconds hand indicates full dead beat seconds and keeps the motion of the wheel train separate from the action of the escapement.
This one-second remontoire tourbillon made for Urban Jürgensen & Sønner represents an entirely new approach to the solving of the problem of inertia, defined as the reluctance of a body to change its state of motion. Previously, watchmakers had sought to overcome inertia by reducing the body mass of the carriage, a technique taken to almost impossible limits by the Deutsche Uhrmacherschule Glashütte under Professor Alfred Helwig.
However, by separating the motions of the escapement from that of the carriage, the problem of inertia is fundamentally overcome. This is achieved by virtue of the remontoire, which in the present watch consists of two concentrically-arranged escapements. The first gives impulse to the balance and has a 15-tooth escape wheel, while the second escapement for the remontoire features a three-tooth escape wheel. A spiral spring is mounted between the two escape wheels fixed on one side to the staff of the 15-tooth escape wheel and on the other side to the staff of the three-tooth remontoire wheel. This spring, which is "set up" or put under tension, is the sole source of impulse to the balance.
Preserved in like new condition, the present twin barrel one minute tourbillon with carriage-mounted remontoire, constant force escapement, jumping dead beat seconds and power reserve is destined to occupy a top position in one of the world's most distinguished collections.
Derek Pratt (1938 - 2009)
The present watch is part of a series of tourbillons on which Derek Pratt worked as chief technician at Urban Jürgensen & Sønner since the beginning of their association in the mid-1970s. Born in 1938 in Orpington, Kent, England, Derek Pratt trained in watch and clock technology at the National College of Horology in London between 1955 and 1959, followed by an apprenticeship at S. Smith & Sons in the English capital. In 1965, he moved permanently to Switzerland and in the following decades worked on the restoration and development of timepieces, including complicated watches and early iron clocks. His impressive body of work includes the present Urban Jürgensen tourbillon, a testimony to the successful collaboration between the creative talent of this master watchmaker and the centuries-old watch manufacture.
During his career, Derek Pratt obtained an impressive number of accolades for his contribution to horology. He was made a Freeman of England's Worshipful Company of Clockmakers in 1979 and a Liveryman in 1982. In 1992, he was honoured with the British Horological Institute's Silver Medal followed by the Tompion Gold Medal in 2005 from the Worshipful Company of Clockmakers. In Switzerland he was awarded the Gaïa Prize, category Craftsmanship-Creation, in 1999. The Gaïa Prize was initiated in 1993 by the curator and directors of the Musée International d'Horlogerie (MIH) in La Chaux-de-Fonds. This international prize is dedicated to Maurice Ditisheim, an early patron of the museum. It is awarded to those who have advanced horology and promoted the arts, history, and culture of timekeeping through their work.
Derek Pratt's other achievements include the English translation of several books on horology with his wife J. Haller Pratt and collaboration on the translation of Daniels' renowned tome "Watchmaking" into French. Derek Pratt himself has also written widely on the subject of horology.