Georges Sagnac

Georges Sagnac (born October 14, 1869 in Périgueux , † February 26, 1926 in Meudon -Belleville) was a French physicist. He is the namesake of the Sagnac effect , a phenomenon that is the basis of the Sagnac interferometer and thus also the laser gyro that has been developed since the 1970s .

Life

Sagnac studied physics at the École normal supérieure from 1890 to 1893 and also at the Sorbonne with a licentiate degree in physics. His teachers included Marcel Brillouin , Gabriel Lippmann , Edmond Bouty and Jules Violle . He then worked as a taxidermist in Bouty's physics laboratory. In 1900 he received his doctorate with a dissertation on X-rays (De l'optique des rayons de Röntgen et des rayons secondaires qui en dérivent). With Pierre Curie , he demonstrated photoelectrons when exposed to X-rays. From 1900 he was Maître de conférences at the University of Lille and from 1904 Chargé de cours at the Sorbonne, from 1912 as professor adjointe. In 1920 he became Maître de conférences for theoretical physics and celestial mechanics around the professors Aimé Cotton and then Anatole Leduc , who held the corresponding chair, to take the lecture (they themselves continued to teach general physics). In 1926 he retired and received the title of honorary professor.

His brother Philippe Sagnac was a historian.

Sagnac was a Knight of the Legion of Honor .

plant

He was one of the first researchers in France to study X-rays (around 1900). He took up Wilhelm Conrad Röntgen's work while he was a laboratory assistant at the Sorbonne .

He belonged to a circle of friends and scientists, including Pierre and Marie Curie, Paul Langevin , Jean Perrin , and the mathematician Émile Borel .

In 1913, Georges Sagnac showed that when light is directed in two opposite directions onto a closed path, which is located on a rotating platform, a phase shift occurs. The ray that moves with the external rotation arrives later than the one that moves in the opposite direction. The theory of this experiment had already been given by Max von Laue in 1911 , who calculated that, according to the theory of relativity as well as the dormant light ether, a positive result could be expected; this effect would only not occur if the ether was completely carried along. Sagnac, however, mistakenly believed that his experiment would only prove the ether and subsequently became an opponent of the theory of relativity.

Franz Harres unknowingly observed the Sagnac effect at the University of Jena in 1912 as part of a Fizeau experiment , which, however, was not noticed until Harzer analyzed the experiment in 1914.

Fonts (selection)

• About the transformation of rayons X par les métaux. Comptes rendus, 125: 230-231, 1897.
• Emission de rayons secondaires par l'air sous l'influence des rayons X. Comptes rendus, 126: 521, 1898.
• About the transformation of the rayons X par les differents corps. Comptes rendus, 128: 546-552, 1899.
• Emission de differents rayons inégalement absorbables, dans la transformation des rayons X par un même corps. Comptes rendus, 128: 300-303, 1899.
• De l'optique des rayons de Röntgen et des rayons secondaires qui en dérivent ... Doctoral thesis, Faculté des sciences de Paris, 1900. no. 380, no. D'ordre 1050.
• Electrisation négative des rayons secondaires produits au moyen des rayons Röntgen . In: Comptes rendus hebdomadaires des séances de l'Académie des sciences . Volume 130, pp. 1013-1016, 1900; online - with Pierre Curie
• L'éther lumineux démontré par l'effet du vent relatif d'éther dans un interféromètre en rotation uniforme . In: Comptes Rendus . Vol. 157, pp. 708-710, 1913;
• Sur la preuve de la réalité de l'éther lumineux par l'expérience de l'interférographe tournant . In: Comptes Rendus . Vol. 157, pp. 1410-1413, 1913;

Individual evidence

1. ↑ Guido Rizzi, Matteo Luca Ruggiero (eds.), Relativity in Rotating Frames, Springer 2004, p. 182