English silver pair cased chronometer pocket watch Circa 1834

Silver watch with Peto Cross chronometer escapement
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An extremely rare English silver pair cased pocket chronometer with a Peto Cross chronometer escapement, according to James Peto, made by John Penlington in Liverpool, circa 1834. The full plate movement with chain and fusee, a spring chronometer escapement, Z shaped bimetallic chronometer balance with two screws and two trapezoidal sliding weights, blued balance spring and set diamond endstone on the balance. White enamel dial with bold Roman hour numerals, an outer minute track, subsidiary seconds at 6 o’clock and spade hands. Both the outer and inner case are smooth and punched with maker’s mark BK. Movement signed and numbered.
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Diameter: 59 mm
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Signed: John Penlington Liverpool
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The Peto cross detent is a rare form of chronometer escapement, seldom used despite the theoretical advantage of having the detent spring in tension as in an Arnold type detent but still retaining an escape wheel without friction. It was invented around 1800 by the British watchmaker James Peto and later used by masters such as Abraham-Louis Breguet.