Swiss yellow gold minute repeating pocket watch Circa 1913

Gold hunting cased keyless lever
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A Swiss 18 carat yellow gold minute repeating hunting cased pocket watch by Patek Philippe & Cie. in Geneva, circa 1913. A solid, polished case, gold hinged cuvette. White enamel dial with Arabic hours, an outer minute track, subsidiary seconds at 6 and blued steel hands. A rhodium plated movement, Geneva striping decoration, 27 jewels, wolf’s tooth winding, counterpoised and straight line calibrated lever escapement, Guillaume balance, cut bimetallic compensation balance, blued steel Breguet balance spring, swanneck micrometer regulator, repeating on gongs activated by a slide on the band. Dial, case and movement are signed.
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Diameter: 55 mm
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Signed: Patek Philippe & Cie.  Geneva
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The Guillaume Balance. Anibal acier au nickel pour balanciers, an alloy invented by Dr Charles Edouard Guillaume, exhibits unusual properties, both in terms of thermal expansion and in changes in elasticity. Around 1900, Guillaume attempted to eliminate the so called Middle Temperature Error caused by the fact that the change of rate in a timekeeper with a steel brass bimetallic balance is approximately a linear function of temperature, while the change of rate caused by a change in the elasticity of a balance spring is approximately a quadratic function. Thus, it equals zero at only two temperatures, causing secondary error. In 1899, Guillaume noted that steel with an addition of 44.4% nickel had a negative square coefficient of thermal expansion. Anibal, combined with brass in bimetallic laminae, makes expansion close to quadratic. Balances with bimetallic rims made of anibal and brass are usually called Guillaume balances.