Georges Sagnac

“ In a system collectively moving with respect to the aether, the propagation time between two arbitrary points of the system must be altered in the same way as it would be in a stationary system subjected to the action of an aether wind, whose relative velocity at each point of the system would be equal and directly opposed to the velocity of that point, and which would carry the light waves in the same manner as atmospheric wind carrying sound waves. ”

“ A uniform clockwise rotation of the interferometer produces a counter-clockwise aether wind; it delays by x the phase of the beam (T) , whose circulation around the area S is clockwise, and it advances the opposite beam R by an equal amount, thus causing a fringe displacement of 2x. The displacement z, that I observe comparing an s image with a d image, must be double that of the former. [2] On the basis of the value of x observed previously (loc. cit. 1910 and 1911) , we have
where indicates the speed of light in vacuum, and λ is the wavelength used. ”

“ In a horizontal optical circuit, at latitude α, the diurnal rotation of the Earth must, if the aether is motionless, produce a relative aether vortex whose density is or radian per second, where T is the duration of the sidereal day ”