Céline Fellag Ariouet

Biography

Céline Fellag Ariouet has worked at the Bureau International des Poids et Mesures (BIPM) since 2005. She is personal assistant to Martin Milton, Director of the BIPM, and heads the Executive and Meetings Department. She is currently working on a doctoral thesis in the history of science at the University of Lorraine on the International Bureau of Weights and Measures from 1875 to 1975, under the supervision of Martina Schiavon.

Conference: Can we keep time?

From invar to elinvar, how Charles-édouard Guillaume revolutionized chronometry and precision watchmaking. Charles-édouard Guillaume (1861-1938), from a watchmaking family based in Fleurier, Switzerland, devoted a career spanning more than half a century to metrological precision at the Bureau International des Poids et Mesures, where he joined in 1883 before becoming director from 1915 to 1936. His work on iron-nickel alloys, which spanned more than twenty-five years and still has numerous applications today, was awarded the Nobel Prize in 1920 and revolutionized not only geodetic measurements, but also chronometry and precision watchmaking. Invar (as in invariable, as its coefficient of expansion is virtually zero) was soon used for pendulum clock rods, which until then had advanced or retarded by a few seconds a day under the effect of temperature. Elinvar (as in invariable elasticity), characterized by a very small variation in its Young’s modulus, was incorporated into chronometer balance springs, giving timepieces up to fifty times greater precision. This talk will retrace the history of these discoveries and what they tell us about the quest for ultimate precision in length and time measurement at the turn of the 20th century.