Charles Édouard Guillaume

Charles-Édouard Guillaume (; 15 February 1861 – 13 June 1938)

Personal life Charles-Edouard Guillaume was born on 15 February 1861 in Fleurier, Switzerland, into a family of French descent. Guillaume received his early education in Neuchâtel, and obtained his Ph.D. in Physics from the Federal Polytechnic School in Zurich (now ETH Zurich) in 1883.

In 1888, Guillaume married A. M. Taufflieb, with whom he had three children.

Scientific career Guillaume was head of the International Bureau of Weights and Measures. He also worked with Kristian Birkeland, serving at the Observatoire de Paris – Section de Meudon. He conducted several experiments with thermostatic measurements at the observatory.

Nickel–steel alloy

Guillaume is known for his discovery of nickel–steel alloys he named invar, elinvar and , also known as red platinum. Invar has a near-zero coefficient of thermal expansion, making it useful in constructing precision instruments whose dimensions need to remain constant in spite of varying temperature. Elinvar has a near-zero thermal coefficient of the modulus of elasticity, making it useful in constructing instruments with springs that need to be unaffected by varying temperature, such as the marine chronometer. Elinvar is also non-magnetic, which is a secondary useful property for antimagnetic watches.

Space radiation Guillaume is also known for the earliest estimation of the "radiation of the stars” in his 1896 article ("The Temperature of Space"). This publication made him a pioneer in plasma cosmology, the study of conditions far from any particular star. The concept was later known as the Cosmic microwave background. He was one of the first people in history to estimate the temperature of space, as 5–6 K.

Publications 1886: Études thermométriques (Studies on Thermometry) 1889: Traité de thermométrie de Precision (Treatise on Thermometry) via Internet Archive 1894: Unités et Étalons (Units and Standards) 1896: Les rayons X et la Photographie a traves les corps opaques (X-Rays) via Internet Archive 1896: 1898: Recherches sur le nickel et ses alliages (Investigations on Nickel and its Alloys) 1899: La vie de la matière (The Life of Matter) 1902: La Convention du Mètre et le Bureau international des Poids et Mesures (Metrical Convention and the International Bureau of Weights and Measures) 1904: Les applications des aciers au nickel (Applications of Nickel-Steels) via Internet Archive 1907: Des états de la matière (States of Matter) 1909: Initiation à la Mécanique (Introduction to Mechanics) HathiTrust record 1913: Les récents progrès du système métrique (Recent progress in the Metric System)