Charles-Edouard Guillaume (1861-1938) was a genius physicist born in Fleurier, Switzerland, who completed his studies in Neuchâtel before obtaining an engineering degree from the Federal Polytechnic School in Zurich. Guillaume joined the International Bureau of Weights and Measures in Paris in 1883, where he worked for 53 years and became its director for 17 years until 1936. Guillaume's work on the alloys of iron, chromium, and nickel led to the discovery of Invar, a substance with almost zero expansion coefficient over a wide temperature range, and Elinvar, a substance with a constant Young's modulus between - 50° and + 100°, which is suitable for the construction of watch springs, tuning forks, springs for seismographs, and more. Guillaume received numerous awards and honors, including the Nobel Prize in Physics in 1920. He retired in 1936 and passed away in 1938 after a long illness.