Swiss silver deck watch with Guillaume balance Circa 1914

Silver open faced lever pocket watch
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A very fine and rare Swiss, keyless, silver deck lever chronometer with Guillaume balance, circa 1914. Accompanied by the Extract from the Archives. A solid, polished case, hinged silver cuvette. Matte silver dial with black champlevé Arabic numerals, outer minute track, subsidiary seconds dial. Blued steel spade hands. The movement was made in 1914, cased in 1941, sold on March 24, 1942. A rhodium-plated movement, Geneva striping decoration, 21 jewels, wolf’s tooth winding, gold wheel train, straight-line lever escapement, Anibal-brass Guillaume balance with gold and platinum timing screws, blued steel Breguet balance spring, swan-neck micrometre regulator. Dial, case and movement signed.
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Diameter: 60 mm
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Signed: Patek, Philippe & Cie.  Genève
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A Patek Philippe deck watch from a small series of about 35, all destined for Observatory trials. Only one example is known in gold.
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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. These properties are very different from those of two other famous alloys invented by Guillaume, Invar and Elinvar. At the end of the 1800s, 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 the change in the elasticity of a balance spring is approximately a quadratic function. Thus, it equals zero at only two temperatures, causing a secondary error. Countless attempts were made to eliminate Middle-Temperature Error, usually by means of auxiliary compensation devices.
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In 1899, Guillaume noticed that steel with an addition of 44.4% nickel had a negative square coefficient of thermal expansion. This alloy, combined with brass in a bimetallic lamina, makes its expansion close to quadratic. Balances with bimetallic rims made of Anibal and brass are usually called Guillaume balances, or, as their inventor called them, integral balances. When combined with special balance springs, they exhibit remarkable temperature stability, on occasion not exceeding 1/50 second per day at 1oC.