Very fine Swiss 18K gold cabriolet pocket watch Circa 1860

Gold cabriolet watch by Patek Philippe
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A very fine Swiss 18 carat gold open faced cabriolet pocket watch, circa 1860. Sold on August 1st, 1865. Lever movement, keyless winding. White enamel dial with Roman hours and outer minute divisions. Cabriolet case, finely engraved. Dial and movement signed, case signed and numbered. Comes with an Extract from the Archives.
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Diameter outer case: 50.5 mm
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Diameter inner case: 43 mm
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A ‘cabriolet’ watch distinguishes itself by two cases conceived for it to be used, either ‘open’ and revealing the dial or ‘closed’ with only the back of the inner case visible. 
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Research shows that less than ten other ‘cabriolet’ watches by Patek Philippe have appeared in public.