Rotary ‘aether drag’

Following observations of the transverse linear Fresnel 'aether drag' (Jones 1972, 1975) it was conjectured that there should be a corresponding angular drag on the plane of polarization of a beam of light traversing a medium rotating about an axis parallel to the direction of the beam. This conjecture was confirmed by Pryce, who found that the angular drag per unit path length should be, to the first order, $\omega (n-n1^{-1})/c$, where $\omega $ is the angular speed of rotation and $n$ the refractive index of the medium. This expression had previously been obtained by Fermi. It has been modified by Player to $\omega (n_{\text{g}}-n_{\phi}^{-1})/c$ by considering the effects of dispersion, where $n_{\text{g}}$ is the ratio of the group velocities in vacuo and in the medium and $n_{\phi}$ is the usual phase refractive index. To detect the effect a laser polarimeter has been developed with a noise level of about $3\times 10^{-8}$ rad for 1 s response time. The paper describes the polarimeter and the precautions that have to be taken in order to detect the rotational aether drag in a specimen rod of Schott SF57 glass, 100 mm long and 20 mm diameter, rotating at speeds of the order 6000 rev/min. The observations appear to support the Player formula rather than others based on phase refractive index or group refractive index alone.