English lever with Bonniksen 52½ minute carrousel Circa 1911-1912

Gold open faced keyless lever by Bahne Bonniksen
–
A very fine and extremely rare English 18 Carat gold open faced keyless lever pocket watch, hallmarked London 1911-1912. Retailed by J. Henry Hobbins, Manchester. Gilt half plate movement with spotted decoration, ring turned pillars, spring barrel, lateral lever escapement, anibal brass Guillaume balance with ‘winged’ arms, gold and platinum temperature and meantime adjustment screws, blued steel Breguet balance spring, diamond endstone, index regulator, whole on Bonniksen 52½ minute carrousel. Gold hinged cuvette. White enamel dial with Roman numerals, outer minute track, subsidiary seconds and original blued steel poire hands. Polished case, master mark FT.  Dial signed by the retailer, Bonniksen patent mark on the pillar plate.
–
Diameter: 52.5 mm
–
Signed: Bahne Bonniksen
–
English watches with Guillaume balances are very rare. Dent and Frodsham used a few, Northern Goldsmiths’ Co, Newcastle-on-Tyne made a few in 1918 and Dreyfuss Moise of London two in 1929. Samuel Smith and Stauffer Co seem to be the two English companies that had the most faith in the Guillaume balance.
–
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 bi metallic balance is approximately a linear function of temperature, while the change of rate caused by 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 bi metallic rims made of anibal and brass are usually called Guillaume balances