Charles-Édouard Guillaume investigated iron-nickel alloys whose thermal changes are unusually small. Invar has low thermal expansion over a useful temperature range, making it valuable for dimensional references. Elinvar addresses a related metrological problem through a small temperature dependence of elasticity, useful when an instrument's behavior depends on an elastic element. These materials show why composition and magnetic behavior can matter as much as geometrical precision when building a stable measuring instrument.[ref]
Invar and Elinvar by Charles-Édouard Guillaume. Nobel lecture, alloy properties and precision-instrument applications
A physicist.[ref]
https://library.ethz.ch/en/collections-and-archives/short-portraits/guillaume-charles-edouard-1861-1938.html. Independent professional biography and identity
Portrait of Charles-Édouard Guillaume
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Charles Édouard Guillaume was a prominent French physicist known for his significant contributions to the field of metrology, particularly in the study of physical constants and the development of precision measuring instruments. He was born on February 15, 1861, and passed away on June 13, 1938. Guillaume is particularly renowned for his work on the determination of temperature scales and the alloy known as Invar, which has a very low coefficient of thermal expansion.