Swiss silver with special patented power source Circa 1898

Silver open faced lever watch
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An interesting and rare, silver and gold Swiss, a keyless pocket watch with a special patented power source, circa 1898. An engine-turned back with polished gold border and bezel, vacant cartouche. Glazed silver-rimmed cuvette. White enamel dial, Arabic numerals, outer minute track with five-minute Arabic numerals, subsidiary seconds. Blued steel spade hands. A Grasset bridge calibre movement, 15 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, the power source in the form of a narrow coiled spring wound around the winding stem which terminates with a contrate gear meshing with the centre wheel pinion. Movement signed.
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Diameter: 50 mm
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Signed: Isaac Grasset & Cie  Geneva