English one-minute tourbillon with centre seconds Circa 1902

Gold full hunter tourbillon by W. & W. Logan
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A very fine and important, English 18K gold hunting cased keyless one-minute tourbillon regulator with centre seconds and special balance spring, circa 1902.
Frosted and gilt, three-quarter plate, calibre 19” movement, 22 jewels, most in screwed settings, pointed tooth lateral lever escapement, cut bimetallic compensation balance with gold poising and timing screws, free-sprung double over coiled balance spring with an outer terminal curve. One-minute tourbillon regulator with polished steel three-arm, Sidney Better style carriage and gilt brass bridge. Enamel dial with Arabic radial hours, outer minutes/seconds track with five minutes/seconds numerals, centre seconds, and original gold spade hands. Plain 18K gold case, London hallmarks 1902.
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Diameter: 56 mm
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Signed: W. & W. Logan
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This is an excellent example of a relatively rare English tourbillon.