Paris: Mallet-Bachelier, 1913. 1st Edition. FIRST EDITION IN ORIGINAL WRAPPERS OF SAGNAC’S “TWO SEMINAL PAPERS” DEMONSTRATING THE SAGNAC EFFECT (Dictionary of Scientific Biography XII). The effect is most simply described as a phenomenon encountered in interferometry; elicited by rotation, it is a phase shift showing “the difference in travel time between two photons traveling along the same path in opposite directions” (Frauendiener, Notes on the Sagnac Effect in General Relativity, General Relativity and Quantum Cosmology, 8.23.18). Today, the Sagnac effect influences precise measurements on Earth and thus are taken into account and routinely incorporated into GPS calculations.
“Together [the two papers offered here] constitute the first interferometry experiment aimed at observing the correlation of angular velocity and phase showing that if a beam of light is split and sent in two opposite directions around a closed path on a revolving platform with mirrors on its perimeter, and then the beams are recombined, they will exhibit interference effects.
“From this result Sagnac concluded that light propagates at a speed independent of the speed of the source” – in other words, that light takes a longer time to travel around a rotating disk in the direction of the motion than against the motion (DSB). However, “motion of the earth through space had no apparent effect on the speed of the light beam, no matter how the platform was turned” (ibid). Sagnac believed that this difference demonstrated the presence of stationary ether.
Seven years after Sagnac’s papers, Paul Langevin derived the Sagnac effect from the equations of general relativity, showing that no ether is required by the effect. The Sagnac effect remained controversial, requiring Langevin to continue to correct scientists who claimed to have shown that the Sagnac experiment is not consistent with relativity.
In today’s world, the “Sagnac effect influences precise measurements on the Earth when using GPS or GNSS. Perhaps not for the general user, but definitely for high precision geodetic type measurements. Apart from effects on the GPS clocks such as the gravitational red (blue)-shift and time-dilation effects, the Sagnac effect involves the second postulate of special relativity (the constancy of the speed of light), the fundamental principle on which the GPS (and other GNSS's) is based” (Ashby, How is the Sagnac effect being used in the GPS system?, Relativity in the Global Positioning System, 2003). Item #1398
CONDITION & DETAILS: Complete volume uncut in paper wrappers with original paper label at the spine. Not ex-library; clean and bright throughout. It is quite unusual to find Comptes Rendus in original wrappers. 4to. 1563 pages. Fully indexed. Very good + condition.
OFFERING: Sagnac Effect. “L’éther lumineux démontré par l’effet du vent relatif d’éther dans un interféromètre en rotation uniforme” and “Sur la preuve de la réalité de l’éther lumineux par l’expérience de l’interférographe tournant” by Georges Sagnac (Comptes rendus hebdomadaires des séances de l’Académie des sciences de l’Académie des sciences 157 No. 17 pp. 708–710 and 1410-1413, 1913).