Swiss 18K yellow gold hunting cased pocket watch Circa 1919

Gold lever pocket chronometer with Guillaume balance
–
A very fine and slim Swiss, 18K yellow gold hunting cased, keyless, lever pocket chronometer with Guillaume balance and 24- hour dial, circa 1919. A polished case, hinged gold cuvette inscribed Nicolai Alexandrovitch Kassianov. White enamel dial with Breguet numerals, outer minute track, inner red painted 24- hour numerals, subsidiary seconds. Blued steel spade hands. A rhodium-plated movement, Geneva striping decoration, 17 jewels in screwed gold chatons, straight-line lever escapement, cut Anibal-brass Guillaume balance, blued steel Breguet balance spring with swan-neck micrometre regulator. Dial and movement signed.
–
Diameter: 51 mm
–
Signed: Ulysse Nardin  Locle & Genève
–
Anibal (Acier au Nickel pour BaLanciers) An alloy invented by the Nobel prize winner Dr Charles Edouard Guillaume, exhibits unusual properties, both in terms of thermal expansion and 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 a 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 using 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 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.