Exceptional Danish gold tourbillon with power reserve Circa 1980

Gold tourbillon by Urban Jürgensen & Sønner
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An exceptional Danish 18 carat yellow gold open faced pocket watch with a one minute tourbillon and power reserve by Derek Pratt, circa 1980. A polished case, glazed back displaying the movement. Silver dial with black painted Roman hour numerals, outer minute track, power reserve at 12, subsidiary seconds and blued steel Breguet hands. Rhodium plated ¾ plate movement, twin barrel winding, bimetallic compensation balance, polished three arm tourbillon indicating seconds, steel flat balance spring with terminal curve. Dial, case and movement signed.
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Diameter: 63 mm
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Thickness: 21 mm
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Signed: Urban Jürgensen & Sønner Copenhagen
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Derek Pratt (1938-2009): Antide Janvier, Abraham Louis Breguet, Ferdinand Berthoud, Harrison and George Daniels are among some of the geniuses of the world of Horology. There is no doubt that Derek Pratt was one of these. Educated at the Beckenham Technical School, his interests were both in horology and light aircraft. In 1956, he started a 3 year course at the National College of Horology as a student apprentice of Smiths. He didn’t complete his course but continued to work for many years with the former school director working on a black box clock for aircraft and on micro electronics.
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This field eventually brought him to Switzerland where his career in watchmaking continued to flourish. A close friend of George Daniels, he was intensely involved in the development of the co-axial escapement and developed the thin version of the escapement as well as several wheels for George Daniels watches. The following three lots are perfect examples of his self discipline and perfection in detail and are an important testament to his genius. This exceptional twin barrel tourbillon was developed by Derek Pratt for Urban Jurgensen. It was unique in the sense that the remontoir was mounted inside the tourbillon carriage.
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His goals when designing this masterpiece were the following:
1. To separate the motion of the wheel train and above all that of the tourbillon carriage, from the action of the escapement. The reason for this was to eliminate the effects of inertia and wear on the escape wheel
2. To provide a practically constant impulse to the balance, independent of fluctuations in the torque applied by the mainsprings, errors in the gear train and any lack of poise in the carriage.
3. To enable the balance amplitude to be set to the desirable angle of 220 degrees with the watch in a vertical plane
4. To indicate complete seconds. For a complete discussion of the development of this caliber, see Derek Pratt, The Watchmaker p. 105 to 155. Detail of the complete escapement with the balance removed. Note the spiral remontoire spring and the stud acting as a stop.