Charles-Édouard Guillaume was born in Fleurier, in the Vaud canton of Switzerland, in 1861. His father was a watchmaker, a context that mattered enormously when, decades later, Guillaume's research at the Bureau International des Poids et Mesures (BIPM, the body responsible for the international standard kilogram and metre) led to a discovery that solved a 200-year-old problem in chronometry.
The problem was thermal expansion. A steel hairspring's elastic modulus and length both change with temperature; a steel balance wheel's diameter changes too. A typical 18th-century pocket-watch lost or gained roughly 11 seconds per day per degree Celsius, meaning a precision marine chronometer needed an elaborate bimetallic balance with weights to compensate for thermal drift. The compensation was never perfect, and chronometer regulation was an art.
"For the service that he has rendered to precision measurements in physics by the discovery of anomalies in nickel-steel alloys."- Nobel Committee citation, 1920 Physics Prize
Guillaume began alloy experiments in the 1890s at BIPM. In 1896 he discovered that an alloy of 36% nickel and 64% iron exhibits a thermal expansion roughly 10 times lower than ordinary steel, close to zero across a wide temperature range. He named it Invar ("invariable"). Two years later he discovered Elinvar ("elasticity invariable"), an alloy of nickel-iron-chromium whose elastic modulus changes minimally with temperature. The two alloys together effectively eliminated thermal compensation as a chronometer-design problem.
Hairsprings made of Elinvar (and its later refinements: Nivarox, Glucydur, Parachrom) replaced traditional bimetallic compensation across the watch industry through the 1920s and 1930s. By 1950 every Swiss chronometer used a Guillaume-derivative hairspring; the bimetallic balance had effectively disappeared. Guillaume served as BIPM director from 1915 to 1936 and continued alloy research through retirement. He died in 1938 in Sèvres.