Pocket chronometer movement with rare duo-in-uno balance-spring, circa 1866.
Hollow-back (no brass-edge), half-plate fusee movement with cap jewels on balance (diamond) and escape, the 18-size frame stamped J.W (Wycherley) and numbered 1866. Spring-detent escapement, the polished steel detent with gold passing-spring. Top quality compensation balance with quarter-timing nuts, blued-steel duo-in-uno balance spring. Signed enamel dial, mismatched hands. 46 mm diameter, 10 mm deep, not including centre arbor.
Edward Sudbury is almost certainly the name of the watches first owner, its number being the date.
NB: The duo-in-uno balance-spring is a combination of helical running into the normal spiral section below, with an Arnold-type overcoil to the top stud. It is a most difficult spring to make and polish. The most likely contender for supplying this movement is John Hammersley who was well known for his chronometer work using this rare form of balance-spring, and which he claimed as his own. This was disputed by two other chronometer makers of similar repute, Arthur P Walsh and John McLennan, both of whom also used duo-in-uno springs.
John Wycherly (1817-91), one of the most important Liverpool makers of rough movements and supplier to most of the best English finishers of his day. He designed his own tooling and standardised English movement sizes, and is holder of Patent No 880, March 1867, for manufacturing "parts of a watch framework to gauge, so that they may be interchangeable"
Some rust on the steelwork, the dial with hair cracks and sadly the detent is also badly fractured and in danger of breaking where the spring section meets the foot. It should be possible, however, to make a working repair, and it does supply a perfect model for anyone considering attempting to make a replacement - size, proportions, jewels, etc. Because of the damage to the detent, this movement is priced accordingly, it's most valuable aspect being the lovely balance-spring which shows no signs of corrosion.
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