Swiss 18 carat gold open faced keyless lever watch Circa 1902

Gold open faced lever chronometer by Patek Philippe
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A very fine and rare Swiss 18 carat gold open faced keyless lever pocket chronometer, circa 1902. Retailed by Bailey, Banks & Biddle Co, Philadelphia. Special movement with patented bridge, wolf’s tooth winding wheels, inset barrel arbor, straight-line moustache lever escapement, cut and compensated bimetallic Guillaume balance, blued steel Breguet balance spring, swan neck micrometer regulator. White enamel dial with Breguet numerals, outer minute track with red five minute numerals, sunken subsidiary seconds and original pierced and engraved gold Louis XV style hands. Polished case, cuvette with dedication inscription. Dial, case and movement signed by Bailey, Banks & Biddle, movement signed by Patek Philippe.
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Diameter: 46 mm
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Signed: Patek, Philippe & Cie Genève
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Anibal (Acier au NIckel pour BaLanciers). An alloy invented by the Nobel prize winner Dr. Charles Edouard Guillaume, it 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. 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 change in elasticity of a balance spring is approximately a quadratic function. Thus, it equals zero at only two temperatures, causing secondary error. Countless attempts were made to eliminate middle temperature error, usually by means of auxiliary compensation devices. 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 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.